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Biology
Preliminary course
Stage 6
Evolution of Australian biota
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Number: 43211
Title: Evolution of Australian biota
This publication is copyright New South Wales Department of Education and Training (DET), however it may contain
material from other sources which is not owned by DET. We would like to acknowledge the following people and
organisations whose material has been used:
Photographs courtesy of Jane West
Part 2 p 19, Part 5 pp
28, 29, 30, 32
Photographs of skulls of extinct fossil Miocene platypus and modern platypus from Grant, T (1995) The
platypus. A unique mammal, University of NSW Press
Part 3 p 29
Sketches of fossil and modern platypus skulls from Musser, A. M. and Archer, M (1998) New information
about the skull and dentary of the Miocene platypus Obdurodon dicksoni, a discussion of ornithorhychid
relationships. Philosophical Transactions of the Royal Society of London, B 353.
Part 3 p 30
Maps of Australia showing average summer and winter temperatures and rainfall. from Australians and
the environment, AUSLIG, ABS 1992
Part 4 p 4
Graphs showing distances moved by platypuses in Thredbo River and body temperatures from Grant, T
(1995) The platypus. A unique mammal, University of NSW Press
Part 4 pp 12, 13
Text extract from Grant, T. R. and Temple-Smith, P. D. (1998) Field biology of the platypus
(Ornithorhychus anatinus) : historical and current perspectives. Philosophical Transactions of the Royal
Society of London, B 353.
Part 4 p 18
Photograph of a rainbow lorikeet courtesy of D. Gonzalvez
Part 5 p 16
Photographs of a young red kangaroo and a young echidna, from Griffiths, M (1978) The biology of the
monotremes. Academic Press
Part 5 pp 22, 23
COMMONWEALTH OF AUSTRALIA
Copyright Regulations 1969
WARNING
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New South Wales Department of Education and Training
(Centre for Learning Innovation)
pursuant to Part VB of the Copyright Act 1968 (the Act).
The material in this communication may be subject to copyright under the Act. Any
further reproduction or communication of this material by you may be the subject of
copyright protection under the Act.
CLI would also like to thank the following people who have contributed to the development of this resource:
Writer:
Tom Grant
All reasonable efforts have been made to obtain copyright permissions. All claims will be settled in good faith.
Published by
Centre for Learning Innovation (CLI)
51 Wentworth Rd
Strathfield NSW 2135
_______________________________________________________________________________________________
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Copyright of this material is reserved to the Crown in the right of the State of New South Wales. Reproduction or
transmittal in whole, or in part, other than in accordance with provisions of the Copyright Act, is prohibited without the
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© State of New South Wales, Department of Education and Training 2008.
Contents
Module overview ....................................................................... iii
Outcomes ............................................................................................ iii
Indicative time...................................................................................... iii
Resources............................................................................................ iii
Icons .................................................................................................... iv
Glossary................................................................................................v
Part 1: New species and the theory of evolution ................. 1-45
Part 2: Plate tectonics and affinities of Australian biota....... 1-35
Part 3: Changing environments and biota in Australia ........ 1-32
Part 4: Adaptations to the Australian environment .............. 1-24
Part 5: Reproductive adaptations ........................................ 1-36
Part 6: Evolution, survival and extinction............................. 1-22
Student evaluation of the module
Introduction
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Evolution of Australian biota
Module overview
The flora and fauna of Australia evolved over millions of years.
During this time the climate changed as well as the position of what is
now Australia.
In this module you will learn about the formation of modern Australia
from its origin as part of Gondwana land until the continent was isolated.
The changing climate over this time affected the plants and animals.
The study of the fossil record and past environments will help you to
understand how our actions can affect ecosystems now and in the future.
Outcomes
This module increases students’ understanding of the applications and
uses of biology, implications for society and the environment and current
issues, research and developments in biology.
Indicative time
This module is divided into six parts. You need to spend at least five
hours on each part. Therefore, the module Evolution of Australian biota
is designed so that you should take at least thirty indicative hours to
complete.
Resources
Part 1:
Introduction
•
at least one plant to observe and measure
•
at least one animal to observe and measure
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Icons
The following icons are used within this module. The meaning of each
icon is written beside it.
The hand icon means there is an activity for you to do.
It may be an experiment or you may make something.
You need to use a computer for this activity.
Discuss ideas with someone else. You could speak with
family or friends or anyone else who is available. Perhaps
you could telephone someone?
There is a safety issue that you need to consider.
There are suggested answers for the following questions
at the end of the part.
There is an exercise at the end of the part for you to
complete.
You need to go outside or away from your desk for this
activity.
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Evolution of Australian biota
Glossary
The following words, listed here with their meanings, are found in the
learning material in this module. They appear bolded the first time they
occur in the learning material.
Introduction
adaptive radiation
increase in the numbers of groups of organisms
evolving from a single common ancestor in
areas with different selective pressures
angiosperms
flowering plants
aquatic
living in water
arid environment
environment where rainfall is very low and
evaporation is very high; an area where
conditions are very dry
artificial selection
increase or decrease in the frequency of
particular genetic characteristics within a
population due to selection by humans
asthenosphere
semi-molten outer layer of the mantle of the
Earth
biota
all species of organism found in a particular
area
browser
herbivore animal which eats shrubs, usually as
well as grass
cellular respiration
the cellular process resulting in the production
of energy for other cell processes
chromosome
structures made up of genetic material (DNA)
and protein found mainly in the nucleus
core
the innermost layers of the Earth, consisting of
a solid inner and liquid outer core
counter-current heat
exchange
arrangement of blood vessels where blood flow
in opposite directions in arterial and venous
vessels causes heat to be retained in the body
convection current
movements within a liquid due to heating
convergent evolution
the independent evolution of similar
adaptations in unrelated groups in response to
similar selection pressures
crossing-over
exchange of parts between pairs of
chromosomes during meiosis
crust
the thin (5-50 km thick) outer layer of the
Earth
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cuticle
waxy layer on the surface of leaves which can
reduce water loss by being impervious to
water; shiny cuticles can also reflect
electromagnetic radiation in the visible band
DNA
deoxyribonucleic acid; - the molecule which
makes up the genetic material of the
chromosomes
endothermic
animals, mainly mammals and birds which
regulate their body temperatures using heat
generated by their metabolism
ectothermic
animals which regulate their body temperature
by using heat from the environment; most
animals apart from mammals and birds
entomology
the study of insects
evaporative cooling
cooling of the bodies of plants or animals by
evaporation of water from the body surface or
from the respiratory system; occurs in birds
and mammals eg. panting in dogs
evolution
change in the genetic make-up of a population
over time
extinction
disappearance of a group of organisms; this
can occur when variations, which permit
survival of some individuals as a result of
changed natural selection pressures, are not
present in the population
fauna
all species of animals found in a particular area
fertilisation
fusion of the nuclei of sperm and ovum in
animals or pollen and ovum in plants
flora
all species of plants found in a particular area
fossil
remains of an organism, or direct evidence of
its presence in rock, ice, amber, tar, peat or
volcanic ash
frequency
number of individuals or structures of a
particular value or belonging to a specific
category (eg. numbers of members in a class
who are a particular height)
gamete
sex cell; sperm or ovum in animals and pollen
and ovum in plants
gaseous exchanges
the exchange of gases between an organism
and its environment; uptake of oxygen and loss
of carbon dioxide in all living organisms;
uptake of carbon dioxide and release of oxygen
in plants
Evolution of Australian biota
Introduction
gene
a unit of inheritance, usually part of a specific
DNA molecule (chromosome)
Gondwanaland
(Gondwana)
southern supercontinent originally made up of
south America, Antarctica, Africa, India,
Australia and New Zealand
grazer
herbivorous animal which eats mainly grass
habitat
the place where a particular organism lives
half life
the time taken for half of a radioactive material
to decay
home range
area or distance used by an animal in its
normal day-to-day activities
homeothermy
maintenance of a stable body temperature
hypothesis
statement of what is expected to occur;
hypotheses (plural) are supported or rejected as
a result of experiments (experiments are used
to test hypotheses)
ice core
long sample of ice collected by drilling into a
glacier or ice sheet
insulation
structures (eg. fat, fur feathers) or changes in
blood circulation (tissue insulation) that reduce
heat loss from the body of animals
inter-glacial
periods between ice ages
Laurasia
northern supercontinent from which North
America and Eurasia originated
mantle
series of middle layers of the Earth, the semimolten outer layer is the asthenosphere
meiosis
process of cell division which gives rise to
gametes; leads to variation in gametes; reduces
the number of chromosomes by half
metabolism
all of the biochemical reactions occurring in
the body; heat is produced as a by-product of
metabolism
monotremes
(Monotremata)
group of mammals which lay eggs; include
two living species of spiny anteaters (echidnas)
and the platypus
mutation
a change within the genetic material which can
be inherited
naturalist
a person who studies the natural history or
general biology of plants and/or animals
collector of scientific information which is
extremely valuable but not always quantitative
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natural selection
increase or decrease in the frequency of
particular genetically controlled characteristics
within a population due to environmental
(selection) agents favouring or acting against
them
nocturnal
active at night
osmoregulation
regulation of salt and water in the body
palaeontology
the study of fossil organisms and their
evolutionary relationships
Pangaea
world supercontinent consisting of the
landmasses originally making up
Gondwanaland (Gondwana) and those of the
northern hemisphere continents which initially
were part of Laurasia
placental (eutherian)
mammal
mammals where there is a complex connection
between the uterus of the mother and the
developing embryo (by the placenta). These
include all modern mammal groups except the
marsupials and monotremes (echidnas and
platypuses)
population
a group of individuals of the same species
living in the same area at a certain time
qualitative
descriptive grouping (eg. large, small, medium
sized)
quantitative
a numerical grouping (eg. 1, 2, 3 or 4 cm)
radiometric dating
estimation of the age of fossils or rocks using
the rate of decay of radioactive elements they
contain
radio telemetry
recording quantitative data on body functions
(eg. body temperature, heart and breathing
rates) using radio transmitters attached to
organisms; permits these data to be collected in
free-living organisms
radio tracking
using radio transmitters attached to animals to
follow their movements and activity
relative dating
estimation of the age of fossils or rocks in
relation to other fossils or rocks of known ages
sclerophyll
hard leafed plants often adapted to withstand
dry and/or fire conditions eg. gum trees of the
genera Eucalyptus and Angophora
selection agent
environmental agents which favour or act
against certain variations in populations
(eg. predators)
Evolution of Australian biota
Introduction
selection pressure
factor(s) in the environment which favour or
act against certain variations in populations
(eg. predation, disease)
species
a group of individuals which can breed with
each other to produce fertile offspring under
natural conditions
speciation
the evolutionary process of formation of new
species
stomate
openings in the surface of leaves controlled
by two guard cells which permit gaseous
exchange and transpiration
terrestrial
living on land
theory of plate
tectonics
the theory that crustal plates and their
associated landmasses move
transpiration
evaporation of water from plants, mainly
through the stomates of the leaves
urea
highly soluble metabolic waste product
produced by most mammals; a lot of water is
needed to excrete this material
uric acid
fairly insoluble metabolic waste product
produced by insects, birds and reptiles; little
water is needed to excrete this material
variation
differences in characteristics of members of
a population; such variations depend on the
genetic make-up of individuals in the
population
vasodilation
expansion of blood vessels to increase blood
flow
vasoconstriction
contraction of blood vessels to decrease blood
flow
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Biology
Preliminary Course
Stage 6
Evolution of Australian biota
Part 1: New species and the theory of evolution
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Contents
Introduction ............................................................................... 2
Genetic variation ....................................................................... 4
Investigation of variations ....................................................................8
Natural selection and evolution ............................................... 11
How does it work?..............................................................................11
Example of natural selection..............................................................14
Charles Darwin........................................................................ 19
Natural selection – whose big idea?..................................................19
Darwin’s studies .................................................................................20
The voyage of the Beagle..................................................................21
Summary................................................................................. 33
Additional resources................................................................ 35
Suggested answers................................................................. 37
Exercises – Part 1 ................................................................... 41
Part 1: New species and the theory of evolution
1
Introduction
Around 170 million years ago (mya) Australia was part of the huge
southern continent of Gondwanaland (otherwise known as Gondwana).
This included the land areas of the Earth now known as Africa, India,
South America, New Zealand and Australia. About 100 mya, towards
the end of the period when the dinosaurs were the most prominent
terrestrial vertebrate fauna, this supercontinent began to break up.
The Australian continent finally separated from Antarctica about
48–38 mya.
As Australia continued to move north towards the equator its geology,
geography and climate underwent considerable change. The process of
natural selection acting on the different individuals within groups of
organisms resulted in the evolution of new species and the extinction
of others.
In this module you will investigate the way in which environmental
changes in Australia over geological time have resulted in the
Evolution of Australian biota.
In Part 1, you will be given opportunities to learn to:
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•
discuss examples of variation between members of species
•
identify the relationship between variation within a species and the
chances of survival of species when environmental change occurs
•
discuss Darwin’s observations of Australian flora and fauna and
relate these to his theory of evolution
Evolution of Australian biota
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In Part 1 you will be given opportunities to:
•
present information from secondary sources to discuss the Huxley –
Wilberforce debate on Darwin’s theory of evolution.
•
perform a first-hand investigation to gather information of examples
of variation in at least two species of organism.
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. Revised November 2002. The most up-to-date version can be
found on the Board's website at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html
Part 1: New species and the theory of evolution
3
Genetic variation
Look around your family, your school or local community and you will
see that all of us look different. You may look very like either your
mother or father. You can probably remember when you were very
young how you might have hated it when relatives made comments like
‘he has his father’s ears’ or ‘she looks just like a younger version of her
Mum’! However, apart from identical twins we all look a bit different
from other members of our families and from other members of
our community.
Of course, all of these variations which we see in people are also found
in all other species as well. Even though the kookaburras or magpies in
your back garden look pretty much alike to you, they really are a bit
different and may also act differently from each other.
The variations which are found in individuals of the same species are
caused by differences in their genetic make-up; they have different
combinations of their genes. You may remember from previous work
that genes are made of DNA (deoxyribonucleic acid) molecules which
make up chromosomes.
All members of the same species normally have the same number of
chromosomes. These chromosomes occur in pairs (eg. humans have
46 chromosomes or 23 pairs); one of each pair coming from the mother
and the other from the father.
The table following shows the numbers of chromosomes found in a
variety of species. You might expect humans to have more
chromosomes than an onion or even a kangaroo, but what about a
platypus or a dog? The number of chromosomes a species has does
not appear to be related to how advanced it is. Some ferns have
250 chromosomes, while humans have only 46!
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Species
Total number of
chromosomes
Number of pairs of
chromosomes
cat
38
19
brush-tail possum
20
10
eastern grey kangaroo
30
15
platypus
52
26
dog
78
39
fern
250
125
onion
16
8
Numbers of chromosomes in various species.
Because chromosomes occur in pairs, genes also occur in pairs except
those that are sex-linked. Normally all individuals of the same species
have a pair of genes for each trait or characteristic. For example, eye
colour or the ability to roll your tongue. But these genes can have
different forms. There is a dark and a light form of the gene for eye
colour, for example. One form of gene for eye colour is different from
the other and can produce a difference in the colour of a person’s eyes.
This depends on which form of the gene they inherit from each parent.
One form of the gene is due to a change from the original. Such a
change is called a mutation.
Mutations occur fairly infrequently and often do not stay in the
population long because they are detrimental (unfavourable) to survival
or reproduction of the individuals that have them. You might remember
that this process is called natural selection. (You will return to this
important process in the next section.)
When a mutation does occur, it can be beneficial in certain environments
or be fairly neutral in its effects so that it stays in the population.
There seems to be little advantage of having light or dark coloured eyes
for example and so the forms of the gene for both colours remains in
our population.
All of the mutations that persist in a population increase the genetic
variation in that population. During the process of sexual reproduction
the genetic variations already present due to mutations are shuffled
around. This occurs during the production of gametes (sex cells), sperm
and ova.
Part 1: New species and the theory of evolution
5
The process of cell division involved in the production of gametes is
called meiosis. In meiosis, chromosomes are independently assorted and
some parts may be exchanged between chromosome pairs (called
crossing-over). Further recombinations of genes also takes place at
fertilisation when there are large numbers of possible combinations of
gametes coming together. This depends on the genetic make-up of the
parents giving rise to the gametes.
You will find out more about these processes later in this module and
also in later modules in the course.
List the processes which lead to increased genetic variation within species.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answers.
When conditions change in the environment occupied by a group of
organisms, this group may not have the necessary characteristics which
will permit the best adapted of them to survive such a change.
As a result, the population may die out or fail to continue reproducing.
However, if there are some individuals in the population that have a
variation which permits them to survive, reproduce and pass this
variation on to their offspring, then the best adapted members of the
group may well survive the change. This is how the process of natural
selection works.
Think about this fictitious example:
It is summer in tropical Australia and it is very hot. The air
temperature has fallen from the middle of the day and as it is nearly
dark, water rats have just come out of their burrows to feed along the
river banks. Most have fairly thin fur, which keeps them warm
enough in the cooler times of winter but does not make them too hot
in summer. However, in this group there is a family whose members
have much thicker fur. It is still too hot for them and they will need to
wait until later in the night before they start feeding. They often
return to their burrows hungry the next morning, as they are too late to
get some of the food available to the others in the population. Times
are hard for this family and their feeding time is so restricted that they
have very little energy left for mating and rearing young. The family
is quite small compared to that of the others in the group.
For some reason there is a change of climate, perhaps due to the
effects of a series of volcanic eruptions producing ash in the
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Evolution of Australian biota
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atmosphere, that reduces the amount of sunlight reaching the area.
It becomes much colder. In this situation, the thick furred water rats
are at an advantage because their thick fur coats insulate them from
the cold, while the others in the population are at a disadvantage.
If the cold climate continues for some time, the offspring of the thick
furred family will have more time to come out to feed in the cold,
while the thin furred rats will need to spend more time in their
burrows sheltering from the cold. They will need to chase around
much more to get enough food to regulate their body temperatures.
The thick furred rats will have more time and energy for breeding.
Over a period of time, there will be an increase in the number of their
offspring, with thick fur coats, and a decrease in those with the
thinner coats.
You will look at the process of natural selection in quite a bit more detail
as you learn more biology in this and other modules in the course.
But it is important for you now to understand how it happens and why
genetic variation is so important to the process.
Next you will be doing an exercise to examine variation in species in
your local area, but before you do, answer the following questions below
to check your progress.
Answer the following questions using the information you have read
so far on genetic variation. The first two are multiple choice questions.
Choose the best answer for each question.
1
Natural selection occurs where:
A) an organism cannot cope with its environment and moves away
B) the individuals in a population best adapted to the environment
survive and reproduce
C) some individuals in a population change their behaviour as the
environment changes so that they can survive and reproduce
D) the environment changes and all of the individuals in a
population become extinct.
2
A mutation is best described as:
A) organisms adapting to a changing environment
B) a change in an individual’s genetic make-up (genes or
chromosomes)
C) a process resulting from sexual reproduction
D) individuals in the population being affected by radiation
Part 1: New species and the theory of evolution
7
3
Most biologists agree that the occurrence of variation within a
population of organisms is very important to the survival of a
species. Why is this so?
______________________________________________________
______________________________________________________
______________________________________________________
Check your answers.
Investigation of variations
Enough reading. It is time to get out and do something. In this activity you
will investigate variations within populations of two species within your
local area.
You have thought about the differences between humans in your family,
class and community, but these differences are hard to measure. Now, you
will look at variations within two species of plants or animals which you can
measure, for example length, width or height.
It is a good idea to use one plant and one animal in your investigation.
Animal species which don’t move around too much and are not damaged
or stressed by you handling them are best eg. garden snails or even
worms from the garden; mussels, oysters or marine snails from a
rock platform.
Hypothesis
It is usual for scientists to make a statement of what they think is
happening and then to take measurements to test the idea. What is
expected is stated as a hypothesis.
For example: ‘It is expected that not all snails measured will be, of the
same size but will show individual variation within the species.’
Method
Decide what species you will use to look at variation. You will need access
to at least 20 of each. Decide what you will measure eg. length of shell,
length of body, number of stripes on the shell, width of the leaf, height of
the plant. You can measure more than one feature for each species.
Follow the steps below.
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Evolution of Australian biota
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1
Describe what species you are measuring, the features you are
measuring and how you are going to measure them. This should be
headed as the Method section of your report.
2
Measure and record each individual’s features eg. height of garden
snail shell for example, 22, 23, 17, 18, 12, 19, 18, 14, 16, 17, 24 mm.
You can see that there is a range of sizes, most of which are different
from each other. You can group those which are similar to each
other so that you have a few groups representing similar heights.
You can use a quantitative (or numerical) way of making groupings.
Alternatively you can use a quality eg. ‘very small’, ‘small’,
‘medium,’ ‘large’ and ‘very large’. These are qualitative
descriptions, such as we use for things like the sizes of some of
our clothes.
3
Record your information in a table. An example is shown below.
Garden snail
Height of shell
category (mm)
4
Banksia
Number in each
category (freq.)
Width of leaf
category (mm)
Number in each
category (freq.)
1-9
1
10-11
1
10-14
5
12-13
5
15-19
6
14-15
4
20-24
3
16-17
3
25-39
0
18-19
1
Use these figures to draw a column graph of the numbers in each
category. Use the graph paper in the Additional resource.
Number in each group
6
5
4
3
2
1
0
1 to 9
10 to 14
15 to 19
Size group
20 to 24
25 to 29
(mm)
Shell height in garden snails.
Part 1: New species and the theory of evolution
9
5
Describe what your measurements show. For example,
‘There was variation in shell height of the snails but there were very
few which had a shell height less than 10 mm and none were longer
than 24 mm.’
6
Your measurements, table and graph should be headed Results
section of your report.
7
Discuss what you think your results show. For example,
‘As expected measurements show that there was some variation in the
heights of the species of snail studied and I accept my hypothesis that
not all snails of the same species have the same size, but show genetic
variation.’
8
You may like to think about factors other than genetic variation
which could affect your conclusions. For example,
‘Although it seems that there is considerable variation within the snail
species in terms of shell height, some of this variation could be due to
growth. Some of the smaller individuals may simply have been
younger.’
9
You could then think about how you could modify your experiment
to get around this difficulty. ‘You may not be able to modify your
actual experiment in this but at least you can think about how you
might. For example,
‘It is possible to tell the age of quite a lot of animal species in some
way. This could possibly have done for the snails and then only
adults were measured in the experiment.’
Complete Exercise 1.1 at the end of this part.
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Evolution of Australian biota
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Natural selection and evolution
Although Charles Darwin is normally associated with the idea of
evolution of species, his grandfather, Erasmus Darwin had already
challenged the idea that all species were created by God and did not
change after their creation.
Erasmus Darwin had suggested that existing species may well have
arisen from earlier forms, but gave no mechanism or process by which
this could have occurred. His grandson came up with this mechanism,
although it was thought of at almost exactly the same time by Alfred
Wallace, a biologist who was working in south-east Asia at the time.
The mechanism, you may remember is called natural selection.
How does it work?
You read about a fictitious example of a population of water rats in the
last section. Now you will examine a more general explanation in six
steps which can be applied to a range of real examples.
Organisms are able to produce large numbers of offspring in their life
time but…
under natural conditions the numbers in a population of a species tend
not to keep increasing. This means that…
most new recruits to a population must die before they can reproduce, so
that there is a struggle for existence and…
there are some winners and some losers. Some members of a population
have genetic variations which make them better adapted to their
environment and so…
these survive and reproduce more quickly than those who are not as well
adapted. This means that the genetic variations of the better adapted are
passed on to the next generations. As a result…
Part 1: New species and the theory of evolution
11
a population will change so that eventually it will be almost entirely
made up of the best adapted individuals. This change in a population is
called evolution.
The process described by the general model, described above can be
summarised as the statement ‘survival of the fittest’. More correctly it
should be ‘survival [and reproduction] of the fittest’. The process only
works if the best adapted individuals pass on their genetic variations
which determine their better adaptation to the environment.
So how does this help with the idea put up by Charles Darwin’s
grandfather that new species can arise from earlier species?
Time is an important part of the answer to this question. The Earth is
around 4.7 billion years (4700 million years) old and so this process of
change has been going on for a very long time indeed. During these vast
periods of time, the climate and geology of the Earth has been changing.
So the environmental conditions experienced by organisms have changed
in different parts of the world and at different times.
Speciation
Populations of the same species may evolve in different ways under
different selection pressures, particularly if they are geographically
separated from each other. Eventually, populations of related organisms
may become so unlike each other that they are recognised as different
species. They may be so different that, even if they were no longer
geographically isolated from each other, they still could not breed under
natural conditions to produce fertile offspring. This process of formation
of new species is called speciation.
So how do we get new groups? How did the reptiles evolve from the
amphibians or birds and mammals evolve from the reptiles?
Good questions. No one was there when this was happening. Our model
of evolution by natural selection suggests that changes between groups
over such long periods of time and under such changes in natural
selection could eventually lead to the evolution of a completely new
group of organisms.
For example, a population of a certain species of reptile may have
become isolated from other populations of that species in a new area with
a very different environment. The isolated group may have changed so
much under the influence of different selection pressures in the new area
over a long period of time, that it would eventually have features so
different from other reptiles that it could be recognised as being an
entirely new group – the mammals. This new mammal group in turn
12
Evolution of Australian biota
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could be separated into different populations in different areas. So, over
time new groups of mammals evolved from this original mammal group
(common ancestor).
There is lots of indirect evidence that suggests common ancestry for the
present large groups of organisms, but you will consider these at another
time in the course. In a later part of this module you will look closely at
how scientists think the flora and fauna of Australia evolved.
Adaptive radiation
The ideas outlined here seem to fit well with the geological and climatic
changes occurring in the Australian land mass once it broke away from
South America and Antarctica and began moving north around 38-45 mya.
These geological and climatic changes would certainly have produced
different selection pressures on groups of organisms geographically
isolated in different parts of Australia.
The evolution of new groups occurred throughout the changing world
and is known as adaptive radiation or divergent evolution.
Adaptive radiation produces new groups from ancestral populations
which have been acted on by different selection pressures in different
parts of the world.
These are not easy ideas. Work back through the material above,
including the model in six steps and then attempt to answer the
questions that follow.
1
Selection pressures are best defined by which statement?
A) Factors of the environment which favour or act against certain
variations in populations.
B) The effect of the weight of the ocean water on organisms living
in the depths of the sea.
C) Ways in which organisms change in response to changes in their
environments.
D) Environmental factors which cause organisms to change their
behaviour so that they can survive.
2
Speciation is the process by which new species are formed.
This process occurs as a result of which following process:
A) Different selection pressures acting on populations of different
species in different places.
B) Different selection pressures acting on populations of the same
species in different places.
Part 1: New species and the theory of evolution
13
C) Different selection pressures acting on populations of the same
species in the same place.
D) The same selection pressures acting on populations of the same
species in different places.
3
Charles Darwin and Alfred Wallace were important to the
development of the theory of evolution because they both:
A) thought that species were created by God and did not change
B) suggested that only individuals which produced the most
offspring survived
C) believed modern organisms evolved from earlier forms
D) thought that natural selection was the mechanism producing
change within species.
4
Adaptive radiation of new species and groups of plants and animals
took place in Australia after it broke away from Antarctica and
moved north. Briefly describe the process by which this adaptive
radiation of many different forms of biota could have occurred.
(Hint: try to use terms like natural selection, geographic isolation,
selection pressure and change.)
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Check your answers.
Examples of natural selection
Although the process of evolution of new species is thought to occur
extremely slowly, the selection of variations in a population which are
most adapted to the environment has been witnessed and studied.
The peppered moth
A good example of selection was carried out in Britain in the early 1950s
by the biologist, H B D Kettlewell. Although it was carried out many
years ago, it is a good example of a study of the importance of variations
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in the process of adaptation to the environment. It also provides an
illustration of how evolution takes place under the influence of
natural selection.
Kettlewell studied a species called the peppered moth (Biston betularia)
which occurs in two different coloured forms (genetic variations), one
dark and one light.
The dark (melanistic) form was always more abundant in populations
around the industrial areas of the country. In those days, before the
stringent air pollution laws of various Clean Air Acts, soot and dust from
smokestacks of factories covered buildings, trees and other objects,
making them dark in colour. Those in non-industrial areas, where trees
were often covered by lichens, were light in colour. In these areas the
populations of peppered moths were mainly of the light (typical) colour.
Kettlewell reasoned that these variations were being acted upon by
different natural selection pressures in the two different areas.
In the industrial areas the dark forms had the advantage of being
camouflaged. When the dark moths rested on tree trunks during the day
they were less obvious to the birds which fed on them, while the light
variation was easily seen and more often taken by these predators.
In the non-industrial areas the opposite was the case–the light coloured
variation was harder to see against the light backgrounds so that fewer
were taken by predators.
Look at the drawings below showing these two forms of moth on typical
backgrounds in industrial and non-industrial areas. You can see that
Kettlewell’s ideas seemed pretty reasonable. He suggested that this
showed natural selection occurring and he set about designing a series of
experiments to test whether he was right.
Light and dark coloured peppered moths against different backgrounds.
Experiment 1: Capture-recapture studies
Kettlewell released 201 light moths and 601 dark ones, which he had
marked with spots of coloured paint, into a polluted woodland near the
industrial city of Birmingham.
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15
If it was true that birds were acting as a selection agent by finding the
light moths more easily, then he would expect that more of the marked
light moths than dark ones would be eaten by birds before they could
be recaptured.
His results showed exactly that: he recaptured 34% of the marked dark
moths but only 16% of the light ones – hypothesis proved? Well, yes but
perhaps it was just that dark ones were more attracted to the light traps.
Kettlewell was a good scientist so he had planned for this and had
included a control in his experiment.
In a woodland in Dorset, a non-industrial area, Kettlewell repeated the
experiment. If it was the light trap which had caused the bias towards
recapturing dark moths, then he would have expected to have still caught
more dark moths in this area as well. However, if his original hypothesis
was correct, it would have been expected that in the control experiment
more dark moths would have been taken by birds and so fewer of these
would have been recaptured. The percentage recaptures are shown in the
table and graph below.
You might like to practise your graphing skills and draw your own graph
from the data in the table. If you have a spreadsheet package on your home
computer, school or workplace you could use it for this task.
Industrial Area
Non-industrial Area
Dark variation
34.0% recapture
6.3% recapture
Light variation
16.0% recapture
12.5% recapture
35
30
% Recapture
25
20
15
Light
10
5
Colour variation
Dark
0
Industrial
Non-industrial
Location
The graphed results of Kettlewell’s mark-recapture experiment.
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The results show that it was not a difference in behaviour between the
two colour forms which had resulted in different capture rates, but was
probably related to the different selection pressures in the two
environments. But could Kettlewell be sure that the birds were the
selecting agent? Not really, from this experiment.
Experiment 2: Predator observations
Kettlewell and his assistants set up shelters or ‘hides’ from where they
could observe birds feeding. They placed equal numbers of both dark
and light moths on trees at the Birmingham site.
Imagine you are a biologist and answer the following self test questions.
1
State a hypothesis for what Kettlewell might have expected to
observe in his experiment.
_____________________________________________________
_____________________________________________________
2
The numbers of each colour variation of moth they saw being taken
by birds in the industrial area is listed below.
•
Dark variation, 15 taken by birds.
•
Light variation, 43 taken by birds.
Do these figures support your hypothesis? ___________________
3
How could you have improved this experiment?
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Check your answers.
Pesticide and antibiotic resistance
Although the study of the peppered moth is a good example of natural
selection acting on variations within a population, there are other
examples which are now becoming familiar to us.
Insecticides, herbicides and antibiotics are all selection agents which
act on the variations within populations of insects, plants or
bacteria respectively.
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17
If the insect, plant or bacterial populations contain individuals with
genetic variations making them resistant to these chemicals, they will
survive and reproduce so that this genetic variation for resistance to the
chemical is passed on to their offspring. Over a period of time the
populations of these pests can become completely resistant to
the chemicals.
We must keep producing new insecticides to protect our crops from
being eaten by insects and new antibiotics to combat bacteria which
cause infections as the genetic make-up of existing populations of these
are changed under the influence of natural selection.
Extinction
It is worth remembering that pesticides and antibiotics can often work
successfully as some of the populations of insects or bacteria on which
they are used have no genetic variations within them that make them
resistant. In this instance all of the population is killed by the chemical.
When a change in the environment occurs in nature, groups of organisms
which do not have genetic variations (that allow some individuals in the
group to survive that change) the group will die out, this is extinction.
While many new species evolve as a result of the action of natural
selection, many others have become extinct under its influence.
Environmental change (probably a fall in global temperature) at the end
of the Cretaceous period (around 65 mya) resulted in the dinosaurs
becoming extinct. Obviously, none of the groups of these species had the
genetic variations which permitted them to survive the selection
pressures of the changed environment.
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Charles Darwin
Natural selection – whose big idea?
The idea that the environment can select the most adapted variations
within a population of organisms had obviously been thought of before
Darwin wrote about it in this famous book On The Origin of Species By
Means of Natural Selection in 1859.
Rather than earlier writings Darwin is remembered because in his
writings Darwin explained his ideas and supported them with many
observations and data he had collected over years of study of the biology
of large numbers of organisms.
The fact that Darwin’s other work in biology had made him famous also
meant that his ideas were noticed by other biologists and by the public.
Actually, there is another very interesting historical example of this
happening. Although Darwin had observed the variations within species,
he had no idea that these variations were genetic. Genes and
chromosomes were unknown at that time. However, in Austria a
Catholic monk by the name of Gregor Mendel had carried out
experiments by breeding garden peas and had worked out that inheritance
was determined by pairs of genes (he called them ‘factors’), one coming
from the gamete of the male parent and the other from the female gamete
during fertilisation.
Mendel published his work in an obscure journal. We know that he was
aware of Darwin’s work but Darwin had never heard of Mendel. In his
writings, Darwin indicated that he worried about how the variations he
observed could have come about and how they were inherited.
These worries could have been eased if he had known of Mendel’s work
with garden peas, but he died 18 years before Mendel’s writings
were ‘rediscovered’.
In 1900, 35 years after Mendel’s work was published, a biologist read his
paper and realised its importance. You will look more closely at the
Part 1: New species and the theory of evolution
19
work of Mendel in the HSC course when you consider genetics in
more detail.
Darwin’s studies
Charles Darwin was born in Shrewsbury, England, on 12 February 1809.
He apparently was quite a good student at school and went on to do
medicine at university in Edinburgh, Scotland in 1825. In his
autobiography he admits to fleeing from an operation on a child where no
anaesthetic was used. He gave up medicine after this event. Both his
father and grandfather were doctors but it was decided that he would
become a minister in the Church of England and he went to Cambridge
University in 1828 to begin his studies. However, he did poorly at his
studies as it seems that his main interests were in geology and natural
history (biology).
When Darwin was 22 years of age, his opportunity to follow his interests
came when he received the offer to travel on the naval ship HMS Beagle.
The Beagle was going on a voyage to survey and map much of the South
American coastline, before sailing around the world via the Galapagos
Islands, Tahiti, New Zealand, Australia and South Africa.
Charles Darwin
Read the information below which describes Darwin’s voyage on the
Beagle. You will use this information in Exercise 1.2.
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The voyage of the Beagle
It was normal for naturalists to go on voyages of discovery in this time.
(You might remember that Joseph Banks was the botanist on Cook’s
voyage to Australia.) But Darwin actually went as a companion for
Captain Fitzroy. This too was not unusual as the officers did not
associate with the other sailors and needed companions to prevent them
going mad from boredom on long voyages. It is interesting that in fact
Darwin and Fitzroy did not see eye-to-eye and were poor companions for
each other.
Darwin, as you might expect from his second choice of career was a
Christian, but Fitzroy was much more devout and in later life he strongly
criticised Darwin’s ideas. Captain Fitzroy was very interested in weather
forecasting but became depressed when he got it wrong – just like the
weather bureau does now! He apparently made a poor job of being
governor of New Zealand and felt responsible for Darwin’s views, which
went against his understanding of the Bible. Fitzroy eventually
committed suicide.
Exploring South America
The Beagle left Devonport in the south of England on 27 December 1831
and sailed to the east coast of South America, arriving on 28 February 1832.
Nearly four years were spent surveying both the east and west coasts
of South America (see the map). During this time Darwin spent time
exploring Brazil (February- July 1832), Argentina (July 1832-May 1834),
Chile and Peru (July 1834-September 1835) and the Galapagos Islands
(September-October 1835). He was seasick almost the whole time and
so spent as much time ashore as he could. Below is a short excerpt from
his Journal describing the seas around Cape Horn.
‘…the sea looked ominous: there was so much foam, that it resembled
a dreary plain covered by patches of drifted snow…
At noon the storm was at its height, and we began to suffer. A great
sea struck us and came on board; the after tackle of the quarter boat
gave way and, an axe being obtained, they were instantly obliged to
cut away one of the beautiful whaleboats [life boats]. The same sea
filled our decks so deep that if another had followed it is not difficult
to guess the result…Captain Fitzroy considers it the worst gale he was
ever in.’
During his time in South America and the Galapagos Islands, Darwin
collected a host of specimens of both fossil and living organisms, as well
Part 1: New species and the theory of evolution
21
as geological specimens. He became intrigued by the similarities of the
organisms he found to those he was familiar with from Britain. Often he
could match these similarities with species from similar habitats. He was
also fascinated however by finding completely different species, both
living and fossil.
After leaving the Galapagos Islands at the end of October 1835 the
Beagle sailed to Sydney via Tahiti and New Zealand. By then Darwin
had tired of the voyage and was resigned to doing little natural history.
He looked forward to some social life in these settled sections of the
British Empire! He wrote in a letter to Professor of Botany at
Cambridge University:
‘During the remainder of our voyage, we shall only visit places
generally acknowledged as civilised and nearly all under the British
Flag. There will be a poor field for Nat: History and without it, I have
lately discovered that the pleasures of seeing new places are as
nothing.’
Darwin obviously assumed that all of the organisms would have already
been studied by other biologists in these areas, but of course he was not
correct. He actually spent quite a lot of time collecting specimens of
plants and animals in Australia, although he did not make a great deal of
use of them in his writings about evolution.
Exploring Australia
Darwin was in Sydney only from 11-30 January 1836, in which time he
made a trip to Bathurst, the furthest west settlement at that time in
New South Wales. He observed quite a few bird species, especially
parrots and saw platypuses in the Cox’s River near what is now the town
of Lithgow.
Darwin also collected rock platform animals and 92 species of insects
around Sydney, including 32 which had not been previously described.
Four of these were subsequently named after him by entomologists
(people who study insects) after he took them back to Britain.
After Sydney, the Beagle went to Hobart, where Darwin had his 27th
birthday. He climbed Mt Wellington behind the town and collected some
plant and animal fossils. Captain Fitzroy set sail from Tasmania on
17 February 1836 and made a final stop in Australia at King George
Sound (now the city of Albany) in Western Australia.
Although they were only in WA for nine days from 6 March 1836,
Darwin hated the place. But he did study the geology, trapped native
bush rats (Rattus fuscipes) and a frog (Crinia georgiana) and collected
fish (20 species), shells, insects and flatworms (planaria).
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Evolution of Australian biota
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Darwin even carried out experiments on planarians from both Tasmania
and Western Australia, observing that, as occurred with the British
species, if they were cut in half they were able to generate both front and
hind ends in around 25 days, so that from one cut animal you could get
two! This process is common in plants, but the flatworms are one of the
few groups of animals in which this occurs.
Darwin apparently quite enjoyed the social life, from which he had been
starved for over four years, when he was in Sydney and Hobart, but in
general was not very impressed by Australia. He wrote in his diary on
March 14 1836:
‘Fairwell Australia, you are a rising infant and doubtless some day
will reign as a great princess of the South. But you are too great and
ambitious for affection, yet not great enough to respect; I leave your
shores without sorrow or regret.’
The table below gives a list of the specimens which Darwin collected or
mentioned during his time in Australia:
Group
Species/type
Where
mammal
platypus
NSW
potoroo
NSW
bush rat
NSW
parrots – probably eastern and crimson
rosellas and king parrots
NSW
birds
sulfur crested-cockatoo
Australian raven
magpie and/or currawong
reptiles
oak skink
Tas
blue tongue lizard
four other lizards
tiger snake
amphibians
southern frog
WA
fish
20 species
WA
Part 1: New species and the theory of evolution
23
insects
molluscs
92 species from five different orders
from around Sydney, including:
beetles, ant lions (lacewing larvae)
NSW
dung beetles
Tas
oysters
NSW
trochid shells
whelk
sand snail
whelk
Tas
periwinkle
amber shell
top shell
crustacea
barnacles
TAS
plants
Casuarina (she oaks)
NSW
tree ferns
grass trees
WA
He also commented on the fact that
native trees were not deciduous and on
the great height of the gums trees on
Mt Wellington in Tasmania
While in Australia, Darwin commented on the similarity between
Australian marsupials and animals from the northern hemisphere.
It is thought that it was in Australia that Darwin began to think about the
evolution of species.
It is interesting to note that Darwin made the following comment in his
Journal in relation to native species in the face of European settlement:
‘It may be long before these animals are altogether exterminated, but
their doom is fixed’
He may have been a bit too severe in his predictions, but at least
17 species of native mammals have become extinct in Australia since
European settlement.
24
Evolution of Australian biota
Part 1: New species and the theory of evolution
SOUTH ATLANTIC
OCEAN
St Helena
Ascension Is
Western
Is
Cape of
Good Hope
Mauritius
Bourbon Is
INDIAN OCEAN
Keeling I
King George’s
Sound
Hobart
Sydney
Bay of
Islands
SOUTH PACIFIC
OCEAN
Tahiti
Society Is
Galapagos Is
Cape Horn
Valparaiso
Falkland Is
Port Desire
Montevideo
Rio de Janeiro
Bahia
Gill Sans Bold
The voyage of the Beagle.
Darwin returns to England
The HMS Beagle returned to England by the Mauritius, Cape of Good
Hope (South Africa), the Ascension Islands and Bahia in Brazil by
2 October 1836.
25
After that time, Darwin worked in London preparing his specimens and
writing his publications from the research on his voyage (ten books in all,
including two editions of his research journals.)
Darwin married in January 1839 and subsequently moved to Kent, where
he became something of a recluse. However, he continued to work on
his writing and the formulation of his thoughts on evolution by means of
natural selection, this had mainly been written and discussed with
colleagues by 1842.
In June 1858, Darwin was overwhelmed when he received a letter from
Alfred Russel Wallace, a biologist working in south-east Asia who had
come up with the same idea as Darwin for how evolution might take
place – he also even called it natural selection! Darwin offered to
arrange for Wallace’s work to be published but his friends and colleagues
wanted Darwin also to receive credit and so organised the presentation of
both their ideas at a scientific meeting of the Linnean Society of London
on 1 July 1858.
Darwin subsequently published his book On the Origin of Species By
Means of Natural Selection in 1859. The title of Darwin’s famous book
is often abbreviated to the Origin of Species. It was an immediate best
seller and of course was very controversial because it appeared to go
against the teachings of the church, which still held that species were
created by God and then remained unchanged.
Darwin left it mainly to his scientific colleagues to argue his ideas in the
scientific community and in public. One of the most famous arguments
was the debate between his friend Thomas Huxley and Bishop
Wilberforce. You will examine this in some detail later in the module.
Unfortunately, the public became mainly interested in the idea arising
from Darwin’s work that humans probably evolved from apes. This was
really just a side issue to the culmination of Darwin’s work.
Darwin’s greatest contribution to biology was in using a host of
information, much of which he had gathered during his famous voyage
on the Beagle, to explain how the mechanism of natural selection could
drive the process of evolution of new species from previously existing
species – the theory which others, including Darwin’s own grandfather,
had proposed much earlier. His Zoology of the Voyage of HMS Beagle
(1838-1843) and two editions of Journals of Research (1839 and 1845)
had been best selling books.
Although he was apparently in quite poor health for much of his life after
returning from his voyage, Charles Darwin lived to 73 years of age and
died on 19 April 1882.
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Darwin’s idea of natural selection
Probably the first thing that gave Darwin the idea of natural selection
acting on variations within a population was something which humans
have been doing since they gave up being nomadic and began to live in
settlements – humans began domesticating animals and plants and
selected the types which best suit our needs.
This process of artificial selection meant that, starting with native
grasses, which produced only small seeds and little flour, the current
grain crops (eg. wheat, oats, barley, rye), were bred which yielded much
more flour when crushed. We have been able to produce breeds of sheep
which produce more wool than they need to keep warm and cows which
produce more milk than would normally be needed to feed their calves.
A good example of how artificial selection can work is seen in breeds of
dogs, ranging from Great Danes to miniature poodles.
Originally, wolf pups would have been adopted into human settlements.
Obviously ones which grew up to be aggressive and dangerous would
have been released or killed, but more docile variations among the pups
would have been selected to breed again. Over a number of generations
these wolves would have become quite domesticated. Other features
could also have been selected, such as an ability to herd cattle and to hunt
or track species used for human food.
Today we have selected for a variety of physical features which we find
appealing in our dogs. Domestic dogs are the same species as the wolf
(Canis lupus) but they have been changed genetically due to artificial
selection. Canis lupus familiaris is a sub species of the wolf species.
Both Darwin and Wallace realised that the environment perhaps could
select the ‘best’ variations in a species and that this natural selection
could lead to the evolution of new species.
During his voyage, Darwin was impressed by the similarities of fossil
and living organisms from different parts of the world. He noted that
there were slight differences between these, which he could often relate
to the habitats in which they lived. One example was a group of small
birds of the Galapagos – the finches.
Darwin found that on different islands, or in different habitats on the
same island, populations of finches had beak shape and sizes which
adapted them to a particular food source. There are large, heavy beaks for
crushing large seeds; sharp beaks for extracting grubs from rotting wood,
small delicate beaks for picking up tiny seeds from shrubs and so on.
The following diagram shows some of the variation in beak shapes in
‘Darwin’s finches’.
Part 1: New species and the theory of evolution
27
Different beak structures in finches found on different islands in the Galapagos.
This illustrates how the species has diverged from the original form.
Current thinking is that these finches probably evolved from one or two
species which were originally blown by wind across from the mainland
of South America, 950 km away. Various populations adapted
differently. This was due to the influence of different natural selection
pressures on the different islands. Eventually these groups became new
species. The original ancestral species had given rise to new species
under the influence of natural selection. You will pursue this idea in
more detail in later parts of this module.
Why were the ideas so controversial?
When he was in Australia, Darwin noted the similarities of the
platypus and the water vole of England both these animals were adapted
for swimming.
He also discussed the fact that the lacewing larva, (or ant lion, in
Australia,) which was definitely a different species from that in Europe,
had the same feeding methods. Both animals buried backwards into
dry soil producing conical holes into which their prey stumbled and
were eaten.
In his Diary, Darwin suggested that surely such similar adaptations in
different species of animals living in similar environments, but in
different parts of the world, indicated that ‘one hand’ must be involved in
producing such similarities. Some people suggest that these entries in his
diary are perhaps an early statement by Darwin of the idea of natural
selection acting.
It seems an obscure reference, but remembering that Darwin realised that
his diary could be read by devoutly religious friends and family back in
England, he could have been wording his ideas in a non-controversial
manner. The ‘one hand’ could have been interpreted as meaning the
hand of God or the action of natural selection. We will never know, but
it is an intriguing aspect of his time in Australia, where we know he did
less biology than in other places and left our ‘shores without sorrow
or regret’.
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Darwin’s ideas were considered controversial because they went against
the belief held by the church at the time that all species were created by
God. As a result, the notion that current species evolved from ancestral
species as a result of natural selection was not acceptable to
many Christians.
Darwin himself knew how controversial they would be, as he came from
a devout Church of England background, and was married to a woman
who was deeply religious. This is probably the main reason that it took
so long for him to make his ideas public and was only really inspired to
make them public by the letter from Wallace in 1858. He had discussed
his ideas with many colleagues in person and by letter long before
this time.
Now do Exercise 1.2.
The Huxley – Wilberforce debate
As mentioned earlier, Darwin was ill for much of his later life and left it
to colleagues to argue his ideas in public and in the scientific community.
This included the famous debate between Darwin’s friend Thomas
Huxley and Bishop Samuel Wilberforce at Oxford University in June
1860, where both of these speakers scored points of debate against
each other.
Wilberforce, reflecting the idea that Darwin’s theory led to the
conclusion that humans had ultimately evolved from a primate ancestor,
supposedly asked Huxley if he traced his ape ancestry back to his
grandfather’s or grandmother’s side of the family. Huxley apparently
replied that he would rather be related to an ape than to a man who used
his position, eloquence and a few hours acquaintance with biology to
ridicule a theory which he did not understand!
However, in reality the nature and outcome of the whole debate is in
dispute as no transcript of it was recorded. There have been numerous
reconstructions of it since, most of which have Huxley ‘winning’ the
debate, while others give the win to Wilberforce or call it as a ‘draw’.
Much of Bishop Wilberforce’s criticism was later published in a
scientific journal and were aimed at Darwin’s methods and reasoning.
The debate is often represented as being between supporters of Darwin’s
theory and the beliefs of the Church, but in reality the debate was of no
great consequence to the acceptance of Darwin’s theory.
There was already a range of reactions for and against the theory of
evolution in both religious and scientific circles. In Australia for
Part 1: New species and the theory of evolution
29
example the reaction to Origin of Species was initially fairly hostile, but
Darwin was actively supported by the geologist W B Clarke who was
also a minister of the Church of England.
Some of Wilberforce’s criticisms are still levelled at the theory of
evolution, particularly by those supporting the idea of special creation,
but biological studies since Darwin’s time have collected information
relating to these criticisms.
Listed below are five of Wilberforce’s criticisms of Darwin’s ideas.
•
Although we can observe change occurring within species
(eg. breeds of dogs) no one has observed it leading to the appearance
of a new species, even in organisms like bacteria which reproduce
very quickly.
•
If earlier groups of organisms gave rise to later ones through the
process of evolution there should be intermediate or transitional
fossil forms found in the fossil record.
•
There are such gaps in the fossil record so it is not possible to trace
ancestry of many species.
•
It might be reasonable to argue that simple variations in a population
(eg. colour in peppered moth) will be selected by the environment
but what about the evolution of complex organs, like the eye of
vertebrates? How could such a complex structure have evolved due
to natural selection?
•
Darwin indicated the reason that we cannot see new species actually
evolving is because the process takes such a long time but it is
scientifically inaccurate to simply say that, given enough time, a
process which cannot be observed will take place.
It has been said that Darwin did not follow the normal scientific approach
of making hypotheses and then testing them, but rather took the approach
of collecting information and then sitting down to work out what it
all meant.
Such an approach is quite acceptable, as it often leads to hypotheses
which are able to be tested by experimentation or further investigation.
This is in fact what has happened.
Other biologists have tested hypotheses arising from Darwin’s theory of
evolution. This has led to a refinement of his theory over the years and
you will examine this in more detail in a later module in the HSC course.
Complete the following questions, then check your answers at the
back of this part.
30
Evolution of Australian biota
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1
Darwin worked out his theory of evolution by using the following
scientific approach.
A) Proposing hypotheses and then going out to collect data to test
these.
B) Making up a theory and then looking at all of the data he had to
see if the data supported the theory.
C) Collecting a range of data and then deriving a theory from the
data.
D) Producing a theory by using second hand data collected from the
observations of other scientists.
2
During his voyage on the Beagle Darwin gathered most of his
scientific data in South America and the Galapagos Islands.
The Beagle also visited Australia where:
A) Darwin spent most of his time socialising after his long time at
sea
B) the weather was so bad that he could not do any biological
collecting
C) many organisms had already been described and studied so
Darwin did not bother to collect more
D) Darwin collected a number of specimens and possibly began to
formulate his ideas on natural selection.
3
The famous debate between Bishop Wilberforce and Thomas Huxley
is often suggested as being an important event in the history of
development of the theory of evolution. Which of the following is
the most correct statement of the importance of the debate?
A) Thomas Huxley convinced all at the debate that Darwin’s ideas
were more acceptable than the idea of special creation.
B) The event was telecast world wide. Millions of people saw it
and Darwin’s ideas gained international acceptance overnight.
C) As it was not transcribed there have been lots of different
interpretations of what was actually said and so it is probably of
little consequence.
D) Wilberforce suggested that Huxley was related to an ape and
Huxley said that he preferred that to being related to a bishop.
Part 1: New species and the theory of evolution
31
4
Some of the criticisms of Darwin’s ideas raised by Bishop
Wilberforce in his review of the Origin of Species are still
considered today to be weaknesses of the theory of evolution.
In your own words outline three of these criticisms.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Check your answers.
In your syllabus you are asked to present information form secondary
sources to discuss the Huxley-Wilberforce debate on Darwin’s theory of
evolution. There is some information that you can use above and there are
some Internet sites on the Science Online webpage.
http://www.lmpc.edu.au/science
Now turn to Exercise 1.3 where you will discuss the Huxley – Wilberforce
debate on Darwin’s theory of evolution.
32
Evolution of Australian biota
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Summary
•
Variations or differences within a species are produced by the
processes of:
- mutation (inheritable changes in genetic material)
- gamete production (meiosis)
- variety of gametes possible at fertilisation.
•
Natural selection acts on variations within populations or species to
produce changes in the characteristics within the group.
•
Natural selection is the mechanism which Darwin and Wallace
suggested was causing changes within populations.
•
Natural selection is this mechanism which also leads to pesticide
resistance in insects and antibiotic resistance in bacteria
•
Over long periods of geological time, and with different selection
pressures on geographically isolated groups of the same organisms
in different environments, the evolution of new species (speciation)
and new groups of species occurs.
Part 1: New species and the theory of evolution
33
34
Evolution of Australian biota
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Additional resources
Part 1: New species and the theory of evolution
35
36
Evolution of Australian biota
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Suggested answers
Genetic variation
The processes that lead to genetic variation within a species are:
•
mutation
•
assortment of chromosomes during gamete production (meiosis)
•
exchange of chromosome parts (crossing over) during meiosis
•
combination of genes produced by fertilisation in sexual
reproduction.
1
B is correct. It is the best adapted species which survive and pass on
their genetic variation to their offspring
2
B again is correct. Although radiation is a cause of some mutations,
a mutation is best defined as a genetic change within an individual.
3
Variation permits natural selection to occur so that a population or
species might survive a change because of a beneficial variation
being present.
Adaptive radiation
1
A
Factors in the environment, such as disease, predation, and
weather permit the best adapted individuals within a population
to survive and to reproduce. This is often referred to as ‘the
survival of the fittest’.
2
B
When groups of the same species are geographically separated
in different places (which have different environments) different
natural selection pressures produce change which can result in
speciation.
3
D
The idea of evolution had been proposed by a number of people
before Darwin, including his grandfather, but the main
contribution of Darwin and Wallace was to propose a
mechanism by which the process took place. That mechanism is
natural selection.
Part 1: New species and the theory of evolution
37
4
As groups of species became geographically isolated from each
other due to geological changes they were exposed to different
environmental selection pressures, especially different climates, and
evolved into new species or groups of species.
Experiment 2: Predator observations
1
You would expect that a greater number of the less well adapted
variation (the less camouflaged light moths) would be seen being
taken by the birds (the selecting agent).
2
Yes, these results do give some support to the hypothesis.
3
You would really need to set up a control observation in a nonindustrialised area to be sure that the birds were taking the colour
variation least well adapted to the particular environment and that
they were not just showing a preference in their feeding behaviour
for light coloured moths.
In fact, Kettlewell did do this and the results are shown in the
table below:
Industrial area
Non-industrial area
Dark variation
15 taken by birds
164 taken by birds
Light variation
43 taken by birds
26 taken by birds
Charles Darwin
38
1
C
It is probable that Darwin had been thinking about the idea of
evolution but it seems that it is likely that he derived his theory
after his experiences and collection of data on his voyages.
A is the approach we most often think of about as being ‘good’
science but it is not the only acceptable scientific approach.
Many biologists have proposed hypotheses based on Darwin’s
ideas and have done experiments or field studies to test these
hypotheses.
2
D
Darwin did in fact do a good deal of socialising in Australia but
also did quite a bit of collecting. He possibly thought about
natural selection leading to the Australian ant lions behaving
like those from Europe and there being superficial similarities
between the platypus and the British water vole.
3
C
There have been lots of articles written about the debate, most of
which come up with different accounts of what probably
happened. The idea that Darwin’s ideas triumphed over those of
the Church seems unlikely. Wilberforce’s review of Origin of
Evolution of Australian biota
Gill Sans Bold
Species, which may have been a large part of his speech at the
debate was even accepted by Darwin, who wrote:
‘I have just read the Quarterly [scientific journal in which the review
was published]. It is uncommonly clever; it picks out with skill all of
the most conjectural parts, and brings forward well all the difficulties’.
4
Go back to the list given in the section on the HuxleyWilberforce debate in the module notes to check your answer.
The apparent weaknesses of the modern theory of evolution will
be discussed in the HSC course. In spite of some weaknesses
the theory is the best we have to explain scientifically how
evolution may have taken place. This idea was stated by Huxley
during the debate, where he reputedly said something like:
‘Without asserting that every part of the theory has been confirmed,
[Huxley] maintained that this was the best explanation of the origin of
species which has yet been offered’
The Athanaeum, 14 July 1860.
Part 1: New species and the theory of evolution
39
40
Evolution of Australian biota
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Exercises - Part 1
Exercises 1.1 to 1.3
Name: _________________________________
Exercise 1.1: Genetic variation
Search your local area for two species to measure. You don’t need to
just stick to size, you might be able to count the numbers of stripes on
shells, numbers with different patterns of markings, different coloured
flowers, leaf length, numbers of leaves and so on.
Make your measurements and write up your results as a report using the
following headings.
Introduction:
What are you going to do?
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Hypothesis:
What do you expect to happen?
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Part 1: New species and the theory of evolution
41
Method:
How did you carry out your experiment?
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Results:
What did you observe? Record your figures, tabulate and graph them
and then describe patterns you observe.
42
Evolution of Australian biota
Gill Sans Bold
Discussion:
Did your results support or go against your hypothesis. What other
factors may have affected your results?
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Exercise 1.2: Darwin
Using an example from your knowledge of Darwin’s activities
and observations during his time in Australia, explain how his
experiences may have contributed to his ideas in evolution
of organisms.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 1: New species and the theory of evolution
43
Exercise 1.3: Huxley – Wiberforce debate
In their debate, it seems that Huxley argued Darwin’s ideas of natural
selection and the evolution of new species and groups from common
ancestry. Wilberforce on the other hand, criticised these ideas. Use the
material from this Part and additional information to answer the
following questions.
a)
Outline two pieces of evidence which may have been used by
Huxley in the debate to support Darwin’s ideas.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
b) Outline two weaknesses in Darwin’s proposed theory which
Wilberforce may have pointed out in the debate.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
c)
Analyse the importance of the idea of natural selection to the theory
of evolution.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
44
Evolution of Australian biota
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d) During its geological history over the 35-45 million years since it
split from Gondwana, parts of Australia have had different climates
and have been isolated from each other by inland seas or by areas of
extremely arid conditions.
Using your understanding of how new species are formed, explain
how such climatic differences and geographic separation could have
lead to changes in the flora and fauna of Australia.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 1: New species and the theory of evolution
45
Gill Sans Bold
Biology
Preliminary Course
Stage 6
Evolution of Australian biota
Part 2: Plate tectonics and affinities of Australian biota
0
20
I
er
b
to T S
c
O EN
g
in D M
t
a
r EN
o
p
or AM
c
n
2
Contents
Introduction ............................................................................... 2
Layers of the Earth .................................................................... 4
Major crust plates .................................................................................5
Plate tectonics........................................................................... 9
Break up of ancient supercontinents.................................................10
Evidence for the theory ......................................................................11
Additional resources................................................................ 25
Exercises – Part 2 .................................................................. 33
Part 2: Plate tectonics and affinities of Australian biota
1
Introduction
In the first part of this module the theory of evolution was discussed,
particularly in relation to the evolution of the biota of Australia.
The evolutionary processes were seen to result from the isolation of
groups of ancestral organisms. This was followed by these groups
changing under the influence of natural selection over long periods
of time.
The theory of plate tectonics explains how this could have come about.
That is, by the northerly movement of the Australian land mass over long
periods of geological time. In this part of the module the theory of plate
tectonics is discussed and its implications for the evolution of the
Australian biota are considered.
In Part 2 you will be given opportunities to learn to:
•
2
identify and describe evidence that supports the assertion that
Australia was once part of a landmass called Gondwana including:
–
matching continent margins
–
position of mid-ocean ridges
–
spreading zones between continental plates
–
fossils in common on Gondwanan continents, including
Glossopteris and Gangamopteris flora and the marsupials
–
similarities between present day organisms on Gondwanan
continents
Evolution of Australian biota
In this part you will be given opportunities to:
•
solve problems to identify the positions of mid-ocean ridges and
spreading zones that infer a moving Australian continent.
•
identify data sources, gather process, analyse and present
information from secondary sources to draw up a timeline that
identifies key events in the formation of Australia as an island from
its origins as part of Gondwana
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. Revised November 2002. The most up-to-date version can be
found on the Board's website at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html
Part 2: Plate tectonics and affinities of Australian biota
3
Layers of the Earth
The Earth consists of a sphere made up of a series of layers. The mantle
and the crust surround the central core. These layers are shown in the
diagram below.
lithosphere
(rigid solid)
oceanic crust
100 km
continental crust
700 km
upper mantle
inner core
1216 km
outer core
asthenosphere
(capable of flow)
mantle
2270 km
2185 km
upper
mantle
700 km
6371 km
Layers of the Earth.
4
Evolution of Australian biota
The crust is the layer that is of most interest in this module.
The crust forming the land areas of the Earth is called the continental
crust. It is between 20 to 80 km thick. Under the oceans is the oceanic
crust that is 5 to 15 km thick). This relatively thin crust is brittle and
cracked like an egg shell into separate plates. These plates are generally
made up of a mix of both continental and oceanic crust. Both types of
crust slide over the semi-molten upper layer of the mantle called
the asthenosphere.
Because the crust is made up of separate plates and these plates are free
to move over the asthenosphere, it is possible for these plates to move
with respect to one another. Of course, this does present problems.
How can the solid plates of the crust move with respect to one another?
The answer lies in the nature of the different crustal plate boundaries.
Major crust plates
The crust of today is broken up into 12 major rigid plates. These plates
are shown and named on the figure below.
Plate
boundry
uncertain
Eurasion Plate
ch
tian
n
Tre
u
Ale
North American
Plate
Basin and
Range Province
San
Andreas
Fault
Him
ala
ys
Caribbean
Plate
Arabian Plate
Philippine
plate
Caroline
Plate
Ja
va
tren
ch
Mid
Atla
ntic
Cocos
plate
Pacific
Plate
Rise
African
Plate
Nazca
Plate
South American
Plate
Ea
st
Pacific
Indian-Australian
plate
ridg
e
Scotia Plate
Antarctic Plate
Antarctic Plate
The Earth's major crust plates. Lines with arrow heads indicate subduction
zones. The arrow heads show the direction of plate movement. The offset or
jagged thin lines within oceans are divergent margins.
Note:
Don’t worry about remembering all the plate names, the
Australian-India Plate (or Indian-Australian) is the one which is
of most interest.
Part 2: Plate tectonics and affinities of Australian biota
5
Plate boundaries
The edges of these plates exist as one of three different types of plate
boundary. Each type of plate boundary is characterised by different
features and events that occur at the boundary. For simplicity geologists
who study plate boundaries describe them as follows.
Divergent (spreading) boundaries.
These form where plates are moving apart such as to the south of
Australia at the present time or where plates are splitting such as in east
Africa. Today divergent boundaries are mainly found on the floor
of oceans.
At divergent boundaries molten rock rises up to fill the space created by
the plates moving apart. The accumulation of this upwelling molten
material forms a volcanic mountain range if it occurs under the ocean and
forms new oceanic crust at mid-ocean ridges. The mountain range is
constantly rifted apart and forms a rift valley along the mid-ocean ridge.
ocean crust
mid-ocean
ridge
rift
continental
crust
A divergent boundary with a mid-ocean ridge.
Divergent boundaries form new oceans or renew the crust in old oceans.
This ensures that the crust of an ocean basin is a maximum of around
200 million years old.
Convergent boundaries
These occur where plates collide with each other and one of the plates
that is denser is forced under the other. You may have already guessed
that if you are making new oceanic crust and splitting plates apart at
divergent plate boundaries you must be destroying crust somewhere else
otherwise the size of the Earth is expanding.
Convergent boundaries can involve different types of situations.
∑
6
Subduction boundaries. These occur where a denser oceanic plate
collides with a less dense oceanic or continental plate.
Evolution of Australian biota
oceanic crust
100 km
200 km
oceanic trench
subducting oce
ani
c lit
hos
asthenosphere
p he
volcanic arc
continental crust
asthenosphere
re
melting
continental lithosphere
∑
The denser crustal plate is forced down under the less dense plate
creating a trench adjacent to the collision zone. This generally results
in volcanoes arising at the edge of the less dense plate.
∑
This type of boundary occurs at the South American and Nazca plate
boundary in Chile and Peru. It has resulted in the volcanoes of the
Andes Mountains and the formation of the Peru-Chile trench on the
west coast of South America.
∑
Oceanic crust can also be subducted beneath other plates made of
oceanic crust. This occurs to the north east of New Zealand along a
structure known as the Tonga- Kermadec Trench. Crust is destroyed
at subduction zones.
oceanic crust
100 km
200 km
oceanic trench
subducting oce
ani
c lit
hos
asthenosphere
p he
island arc
re
melting
∑
continental crust
asthenosphere
continental lithosphere
Continental collision boundaries occur where two continental plates
collide. This results in mountain formation. The most prominent
example of this occurring is where the plate India is attached to is
colliding and being forced under the Eurasian Plate. The mountain
range that has formed as a result is the tallest in the world today,
the Himalayas.
Part 2: Plate tectonics and affinities of Australian biota
7
100 km
200 km
asthenosphere
Continental lithosphere
Continental lithosphere
Closer to home the highlands of New Guinea were formed when the
Australian-India (Indo-Australian) plate collided with the largely oceanic
plates to its north.
Transform fault boundaries
These boundaries form where plates are moving past each other.
At transform faults crust is neither created nor destroyed. This occurs
along the north-south axis of New Zealand, where the Pacific and
Indo-Australian plates move past each other. This structure is the Alpine
Fault. Another well known transform fault occurs on the west coast of
the USA. Part of this fault is the famous San Andreas Fault that runs
through California.
fault plane
A transform fault boundary
The driving force of plate tectonics is trench pull and trench push.
Look at the map of the major crust plates shown previously and locate each
of the features and plates discussed.
Complete Exercise 2.1.
8
Evolution of Australian biota
Plate tectonics
The idea that landmasses drifted across the face of the Earth was first
seriously suggested by Alfred Wegener in 1912 in his theory of
continental drift. He proposed the idea that continents moved around the
globe because he could see no other way to explain the reason for the
similarities in rocks, fossils and other geological features on either side of
the Atlantic Ocean. Much of Wegener's hypothesis of continental drift
was based on the apparent geographic fit of the bulge of eastern South
America and the western coast of Africa. He even went as far as to
envision a single great landmass, Pangaea, which supposedly began to
separate in the Triassic Period around 250 to 208 million years ago.
Wegener had no mechanism to explain how the continents could be
moved so his theory of continental drift was thought to be rubbish by
most scientists. Wegener’s hypothesis languished for the next four
decades though the observations he had made supporting continental drift
remained unexplained.
In 1962 Harold Hess of the USA suggested that convection currents in
the molten part of the mantle were the driving force for the movement of
continents. He suggested that new sea floor is created at mid-ocean
ridges and spreads away from them as it ages. Sam Carey of Tasmania
suggested the concept of a subduction zone in the late 1950s.
Neither had any direct evidence for these ideas and both were criticised
for a nonscientific approach to a problem. Their hypotheses were
important as over the following two decades evidence would show their
ideas to be largely correct.
Until the 1990’s it was assumed that convection was the sole driver of
plate motion with slow movement of the mantle dragging the overlying
plates along with it. Since 1994 the ideas of Professor Seiya Uyeda
(Tokai University, Japan) that subduction is the major driver of plate
motion are becoming increasingly popular. Professor Uyeda’s arguments
are simple. The subducting dense slab literally drags the plate behind
it along.
Part 2: Plate tectonics and affinities of Australian biota
9
There may well be some contribution from convection currents in this
motion and some wedging apart of plates in a process known as ridge
push but this contribution is difficult to quantify.
Interestingly much debate is occurring today on this concept and it still
remains a controversial question in geology. In doing any reading on the
subject be aware that Professor Uyeda first published his ideas in 1994.
Older books will therefore not consider trench pull as a mechanism of
plate motion. This is a case of an idea in science being born and gaining
in impetus. It is still not universally accepted.
Now you will look at the evidence that has turned the concept of
continental drift into the theory of plate tectonics.
Break up of ancient supercontinents
From around 280 mya all of the major current northern and southern
hemisphere continents were joined into one landmass called Pangaea.
Gondwana formation
About 225 mya Pangaea began to break up as the crustal plates began to
move apart. The first division was between the northern supercontinent
(Laurasia) and the southern giant landmass of which Australia was part.
This southern supercontinent is called Gondwana (or Gondwanaland).
Separation was not immediate and took close to 50 million years to
complete. During this time there was a northward drift and slight
anticlockwise rotation of the Gondwanan continent.
Africa
South
America
Madagascar
India
Australia
Antarctia
Gondwana is the former supercontinent in the southern hemisphere. It included
South America, Africa, peninsular India, Australia and Antarctica.
The name Gondwanaland was coined by the Austrian geologist Eduard
Suess who named it from the Upper Paleozoic and Mesozoic formations
10
Evolution of Australian biota
of the Gondwana region of central India, which display typical
developments of many of the shared geologic features that are evident on
all separated fragments of the former supercontinent.
Separation of Gondwana
Gondwana finally separated from Laurasia around 170 mya and
then it began to break up around 100 mya into the current
continental arrangement.
The isolation of Australia
About 45-35 mya the Indo-Australian plate finally broke away from
Antarctica completely and drifted north, colliding with the plates of
south-east Asia about 15 mya.
To see an animation of the break up of Pangaea to the present day
configuration of continents see the Biology page of the science website at:
http://www.lmpc.edu.au/science
Evidence for the theory
The theory of plate tectonics, like Darwin’s theory of evolution, became
accepted as evidence was collected for its support. Although it is not
necessary in a biology course to investigate this evidence thoroughly, it is
important to understand why the theory is now widely accepted, as its
implications are important to evolutionary biology (considered in Parts 1
and 3 of this module.)
The evidence that you will be considering is:
•
matching continent margins
•
position of mid-ocean ridges
•
spreading zones between continental plates
•
fossils in common on Gondwanan continents, including Glossopteris
and Gangamopteris flora and the marsupials
•
similarities between present day organisms on Gondwanan
continents.
Part 2: Plate tectonics and affinities of Australian biota
11
Matching continent margins
Evidence to support this theory came from the jigsaw fit of the shape of
continents. By the 1600s much of the world's landmasses had been
mapped. In 1620 Francis Bacon pointed out the similarities in shape
between the continents on either side of the Atlantic Ocean. As well as
visibly matching further research found that the margins of the continents
shared other similarities such as the type and age of rocks and the
presence of earthquakes and volcanoes along the continental margins.
Rock types
The continents are not a perfect jigsaw fit, and so you might reject the
idea that they were once joined into one continent. However, geological
investigations have shown similarities in rock types between Africa and
South America. The figure below shows some similarities in rock
formations between the two continents (the same rock formations are
shown by the same shading on both continents.)
The probable position of South America and Africa in Gondwana. Areas of
similar rock types shared between the two continents are shown as
shaded areas.
One problem with simply matching coastlines of continents is that the
continental shelves are the true boundaries of the continents.
12
Evolution of Australian biota
Earthquakes and volcanoes
Earthquakes and volcano patterns provide additional evidence for
locating and determining the nature of plate boundaries. When the
earthquake epicentres (where the earthquake actually occurred) are
plotted on a map they form narrow zones that delineate the edges of
crustal plates. Areas of volcanic activity are also found along
plate boundaries.
This is a bit like a complicated join-the-dots puzzle. The map following
shows the location of the Earth’s volcanoes. Try to join up the dots on the
map, as they should show the crustal plate boundaries.
Location of the Earth's volcanoes.
Is it a bit hard to do? It should help if you look at the next map, which
shows the epicentres of earthquakes. Remember that both earthquakes
and volcanic activity occur along plate boundaries. How did you go this
time mapping the plate boundaries?
Part 2: Plate tectonics and affinities of Australian biota
13
Earthquake locations on the surface of the Earth
There are a few volcanoes and earthquakes areas found away from plate
boundaries, but overall the earthquake and volcanic zones are a good fit
for the plate boundaries.
Some volcanoes form in lines or chains away from the crust boundaries
such as the Hawaiian-Emperor Seamount chain and the line of extinct
volcanoes on the eastern extent of mainland Australia eg. the
Warrumbungles, Mt Kapatur, Mt Warning and the Glasshouse
Mountains. These are thought to have formed as the plate moved over a
stationary hot spot in the mantle that literally burned its way through the
crust periodically. The fact that these mountains in the chains each
become older in one direction suggests the plate on which they formed
is moving over the hotspot and supports the concept of crustal
plate movement.
Age of rocks
Ages of rocks on continental margins that were thought to have been
joined support continental drift. When the ages of rocks are determined
by radiometric dating methods and compared across continents, the
ages of rocks on the margins, that were probably joined to each other, are
the same and therefore could have been attached to each other as the
theory suggests.
14
Evolution of Australian biota
Position of mid-ocean ridges
The ocean floor is not flat. As same as on the land, there are plains,
mountains and valleys.
Mid-ocean ridges are volcanic mountain chains. They rise kilometres
above the deep-sea ocean floor and are over 50 000 kilometres long.
They are the longest chains of volcanoes on the planet. They are formed
by the plates spreading. As the plates move apart the gap is filled
with magma.
The evidence for the position of mid-ocean ridges comes from
magnetism and radiometric dating of the sea floor.
Magnetism
The structure and age of magnetic anomalies adjacent to apparent
divergent margin zones around Australia suggest a history of sea floor
spreading and the path of the Australian continent’s drift.
Early in the 20th century, palaeomagnetists such as Bernard Brunhes in
France and Motonari Matuyama in Japan studied the Earth's ancient
magnetic field. They recognised that igneous rocks like basalt (that make
up most of the ocean floors basement rocks) belong to two groups
according to their magnetic properties. One group has normal polarity.
That is, the magnetic minerals in the rock have the same polarity as that
of the Earth’s present magnetic field. This would result in the north end
of the rocks ‘compass needle’ pointing toward magnetic north. The other
group of rocks, however, have magnetic minerals with reversed polarity,
indicated by a polarity alignment opposite to that of the Earth's present
magnetic field. In this case, the north end of the rocks compass needle
would point south.
Part 2: Plate tectonics and affinities of Australian biota
15
Mid-ocean ridge
3
2
lithosphere
1
1
2
3
magma
Stripes 1, 2 and 3 are the same age
either side of the Mid-ocean ridge
normal magnetic
polarity
reversed magnetic
polarity
Magnetic polarity of the sea floor.
Scientists wondered how this could be? This answer was simple.
Grains of magnetite behave like little magnets and can align themselves
with the orientation of the Earth's magnetic field. When molten rock
containing minerals and gases cools to form solid volcanic rock, the
alignment of the magnetite grains is locked in recording the Earth's
magnetic orientation or polarity as normal or reversed at the time of the
rocks cooling.
During the 1950s as the sea floor was mapped using sensitive
magnetometers that record the polarity of seafloor rocks. The magnetic
stripes or magnetic variations turned out to be common recognisable
patterns. In fact, these magnetic patterns over the ocean floor showed a
zebra-like pattern. Alternating stripes of magnetically different polarity
rock were laid out in rows on either side of mid-ocean ridges.
These became known as magnetic anomaly patterns.
The meaning of these magnetic stripes was finally determined by Vine
and Matthews from Cambridge University in Britain in the 1960s, but not
before two United States scientists Cox and Dalrymple studying
magnetic reversals on land, developed a time scale of magnetic reversals.
Vine and Mathews combined the magnetic time scale of reversals and the
magnetic stripes on the ocean floor to show that the rate of spreading of
the sea floor from the mid-ocean ridge divergent margin could be
determined from magnetic stripe patterns.
16
Evolution of Australian biota
Ocean floor dating
Sediments containing fossils that can be easily dated increase in
thickness and maximum age on either side of a mid-ocean ridge as the
distance from the ridge increases. This suggests the points most distant
from the mid-ocean ridge are the oldest and the points at the ridge are
the youngest.
Radiometric dating of the ocean floor rarely shows an age in excess of
200 million years suggesting that the sea floor is very young and often
recycled compared to continental crust. The radiometric ages of sea floor
also increases away from the ridge.
Spreading zones between continental
plates
Evidence for sea floor spreading comes from exploration from deep-sea
submersibles. In 1977 an expedition near the Galapagos Islands
discovered hydrothermal vents. The importance of this discovery was
that the existence of these areas had been hypothesised but never before
seen. It was a location where new planetary crust is formed as the
injection of new basalt moves the plates apart.
This discovery was followed by the discovery of ‘black smokers’.
These are areas where superheated water is discharged from the sea floor
loaded with sulfides. These precipitate as they hit the cooler water and
have the appearance of black smoke, thus the name. The discovery was
exciting because at these sites there is whole community of living
organisms relying on chemosynthesis as a basis for life.
Fossils in common on Gondwanan
continents
Fossils provide some evidence of continents being joined or separate in
the past. If the continents were joined at some stage, you would expect
that fossils or ancestral groups of present day organisms, or even living
representatives in common would be found in the modern continents that
made up the previous supercontinent.
Similarly, if a species or group evolved on one of the continents after it
had broken away from the supercontinent, you wouldn’t expect to find it
on the other separated continent. The evidence from fossils supports
these expectations.
Part 2: Plate tectonics and affinities of Australian biota
17
Fossils of ancient Glossopterid plants (eg. genera Glossopteris and
Gangamopteris), which evolved around 280 mya, are found in Australia,
Antarctica, South America and also in India. Remember that India was
also once part of Gondwana.
Fossils of Glossopteris. (Photo © LMP Tim Reid)
Similarities between present day
organisms on Gondwanan continents
Plant and animal distribution on modern continents supports the concept
of continental drift having taken place. The widespread distribution of
many species of plants and animals either as living organisms or as
fossils on separate continents suggest a link in the past.
The kauris, Norfolk Island pine, Hoop pine, Bunya pine and the recently
discovered Wollemi pine, belong to the plant family Araucariaceae,
which occurs in Australia, New Zealand and South America.
18
Evolution of Australian biota
Araucaria luxurians found on New Caledonia.
(Photo: Jane West)
Close-up of a Wollemi pine. (Photo: Jane West)
The King Billy and Pencil pines from Tasmania are species from the
redwood family, which is mainly found in the northern hemisphere.
The ratite birds include ostriches of Africa, the rheas of South America,
the emus and cassowaries of Australia and the kiwis (and extinct moas)
of New Zealand. The occurrence of bird species is often not a good
indicator of affinities between landmasses, as they can reach very distant
areas by flying. However, the large ratite birds could not have flown to
colonise the newly divided continents and so indicate that the continents
were once joined.
The southern beech trees (Nothofagus) were also found throughout
Gondwana before it broke up. Living species of Nothofagus currently
occur in Australia, New Zealand, New Caledonia, New Guinea and
South America. Fossil pollen of Nothofagus has also been found
in Antarctica.
Some animal groups have been found as living species in Africa, South
America and Australia. For example, the ratite birds (mainly large
flightless species) and lungfishes. Others, which presumably evolved
after Africa had split from Gondwana, include the parrots, gecko lizards,
some bird species.
Part 2: Plate tectonics and affinities of Australian biota
19
Many species of vertebrate animals that inhabited Gondwana have left
descendants in the separate continents that once made up the
supercontinent, including Australia. These include the marsupials and
monotremes. Marsupials are pouched mammals that occur mainly in
Australia. Other Gondwanan countries such as South America also have
a range of marsupials. Marsupials and monotremes will be considered in
more detail in the next part of the module.
Collision with south-east Asia
The Indo-Australian Plate is still carrying the Australian landmass north
at a few centimetres per year. You now know that the Australian land
mass has not always been in its current position, but was once grouped
together with the other Gondwanan fragments into a supercontinent,
which eventually split up as the component plates split apart and drifted
in relation to each other. The question is what effect has this had on the
Australian biota?
When the Australian landmass came close to south-east Asia many
species of organisms eventually found their way via the islands between
the south-east Asian mainland and Australia. These immigrants included
most of the rodents (rats and mice), the bats and the group to which most
of the dangerous Australian snakes belong (family Elapidae).
A number of groups of native biota have reached Australia in the last
15 million years, especially during the times of the ice ages, when sea
levels fell and strips of land existed between many islands, including
between New Guinea and northern Australia.
Complete Exercise 2.2.
The isolation of Australia
About 45-35 mya the Indo-Australian plate finally broke away from
Antarctica completely and drifted north, colliding with the plates of
south-east Asia about 15 mya.
To see an animation of the break up of Pangaea to the present day
configuration of continents see the Biology page of the science website at:
http://www.lmpc.edu.au/science
The table below records the events that lead to the break-up of Pangaea
and then Gondwana. As Gondwana broke up Australia became isolated
from the other Gondwanan countries.
20
Evolution of Australian biota
Era
Period
Epoch
Time spans
(million years)
Quaternary
Recent
10 000-today
Pleistocene
Cainozoic
Tertiary
Events
2 million-10 000
Pliocene
5-2
Miocene
25-5
Oligocene
40-25
Eocene
55-40
Paleocene
65-55
Cretaceous
140-65
Indo-Australian plate collides
with south east Asia
(approx.15 mya)
Australia drifts north
(approx.45 mya)
separation of New Zealand and
Lord Howe rise (approx. 80
mya)
separation of India approx. 100
mya)
Mesozoic
Jurassic
210-140
separation of Africa (approx.
125 mya)
rift between west and east
Gondwana (approx. 150 mya)
Pangaea rift from Gondwana
(approx. 170 mya)
Triassic
250-210
Permian
300-250
The first split was an unzipping of Gondwana from east to west
approximately 150 million years ago. To the east were Antarctica,
Australia and India. To the west was South America and Africa.
Africa then separated from South America 125 mya. India moved away
100mya and New Zealand separated 80 mya. Australia separated from
Antarctica 45 mya and collided with southeast Asia 15mya.
Part 2: Plate tectonics and affinities of Australian biota
21
Geological time line
Because geological time is so immense it is often difficult to conceive the
length between different periods. For that reason a timeline is a good
tool to help you to visualise time. In the Additional resources section
there is a timeline partially constructed for you. Use this or if you prefer
make one yourself. The instructions for constructing your own are also
in the Additional resources section.
Here is a list of the things which you should put on your time line, but
don’t limit yourself to the ones given (eg. you could note the time of the
separation of Africa and India, or the time India crashed into the
Eurasian plate):
Start at the Permian period (about 300 mya), when Australia was still
attached to the large supercontinent of Pangaea, through the separation of
Gondwana and the progression of the separate Australian continent north
until its collision with south-east Asia about 15 mya.
On the timeline mark:
•
the important eras, periods and epochs (Permian, Triassic, Jurassic,
cretaceous, tertiary, Quaternary
•
separation of Gondwana from the rest of Pangaea
•
separation of east (Antarctica, Australia, India) and west (South
America, Africa) Gondwana
•
separation of New Zealand
•
separation of Australia
•
separation of south America
•
Indo-Australian plate colliding with south-east Asia.
Note: you will need to refer to your notes and the Additional resources to
do this exercise.
This exercise will help you to become familiar with the timing and names
of the geological periods and epochs, which aren’t easy to learn just on
their own. All of the information you need to do this assignment are in
the learning material of this part, but if you like you can consult other
sources such as books, CD ROMs or the Internet.
Two very useful references for this part may be available from your
local, school, or TAFE library or they could get them for you.
22
Evolution of Australian biota
•
Lewis, G B. 1995. Plate Tectonics. Teacher Notes and Student
Activities. Australian Geological Survey. Geoscience Education
Record.
•
Lewis, G B. 1995. Time and Life. Geological time and
Palaeontology. Teacher Notes and Student Activities. Australian
Geological Survey. Geoscience Education Record.
Complete Exercise 2.3. Send in your completed timeline.
Part 2: Plate tectonics and affinities of Australian biota
23
24
Evolution of Australian biota
Additional resources
Note: You can skip these steps and choose to use the prepared time line
following.
Instructions for making your own time line
You will need to either get some continuous paper (eg. unwaxed kitchen
paper or roll of wrapping paper) or stick A4 pages together.
How long a piece of paper will you need? Remember that the Earth is
about 4500 million years old but you don’t need to make your time line
to cope with that length of time. You should start your time line at the
beginning of the Permian Period (300-250 mya) when Australia was still
part of the supercontinent of Pangaea. There are two ways of doing it:
Method 1
Decide how many years you will allocate to each unit of measurement of
your line.
eg. 1 cm = 1 million years, your paper will need to be 3 m long
(300 cm = 3 m)
eg. 1 cm = 10 million years, your paper will need to be 0.3 m (30 cm)
long (3000/10 cm = 30 cm = 0.3 m)
3 m might be a bit long to handle and 30 cm not long enough to fit things
in, so you need to get something in between.
Method 2
Decide how long your paper is going to be and then work out how many
millions of years are represented by each unit of measurement.
You can use the following equation to work it out:
1 cm will = 300/(length of paper in metres x 100) million years
Part 2: Plate tectonics and affinities of Australian biota
25
If you decide that your paper will be 1.5 metres long then:
1 cm will = 300 / (1.5 m x 100)
= 300 / 150
= 2 million years
You now need to calculate the length of the period and then divide this
by the numbers of millions of years equivalent to 1 cm on your time line:
For example Permian period 300-250 mya = 50 million years
Distance on time line = 30/2 = 15.0 cm
Triassic period 250-210 mya = 40 million years
Distance on time line = 40/2 = 20cm
You will have to experiment a bit until you get a scale with which you
are happy. The table following shows the main eras, periods and epochs
along with their time span. By the end of this module you should be
familiar with the order in which they occur and have some idea of how
long they were. This is pretty well impossible to do immediately, but by
the time you have worked through the learning materials and done the
activities and assignments of this module you will find that it isn’t too
hard. It is a bit like learning a language other than your own native one.
The more you make use of it the better you get.
26
Evolution of Australian biota
millions of years ago
100 90
80
70
60
50
40
30
20
10
0
Join the next three pages together.
Part 2: Plate tectonics and affinities of Australian biota
27
28
Evolution of Australian biota
Part 2: Plate tectonics and affinities of Australian biota
29
millions of years ago
200 190 180 170 160 150 140 130 120 110
100
Isolation of Australia time line
30
Evolution of Australian biota
Part 2: Plate tectonics and affinities of Australian biota
31
millions of years ago
300 290 280 270 260 250 240 230 220 210 200
32
Evolution of Australian biota
Exercise – Part 2
Exercise 2.1 to 2.3
Name: _________________________________
Exercise 2.1: Plate boundaries
Volcanic activity and/or earthquake activity normally occur along plate
boundaries. The diagram below shows a section of the crust that
includes a convergent boundary a divergent boundary, and a
transform fault boundary. Locate and circle each of these boundaries
on the diagram.
continental crust
oceanic crust
rift valley
(divergent convergent
boundary) boundary
divergent
boundary
oceanic crust
convergent
boundary
transform fault
convection cells
plate movement
Exercise 2.2: Evidence for Gondwana
The evidence for Australia being part of Gondwana comes from various
sources including the ones given below. In each area give an example of
a source of evidence.
Part 2: Plate tectonics and affinities of Australian biota
33
a)
matching continent margins
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
b) position of mid-ocean ridges
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
c)
spreading zones between continental plates
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
d) fossils in common on Gondwanan continents
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
e)
similarities between present day organisms on Gondwanan
continents.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
34
Evolution of Australian biota
Exercise 2.3 : Timeline
Attach your completed time line and return to your teacher.
Part 2: Plate tectonics and affinities of Australian biota
35
Gill Sans Bold
Biology
Preliminary Course
Stage 6
Evolution of Australian biota
Part 3: Changing environments and biota in Australia
0
20
I
er
b
to T S
c
O EN
g
in D M
t
a
r EN
o
p
or AM
c
n
2
Contents
Introduction ............................................................................... 2
Geological time scale and biota ................................................ 4
Evidence of changing environments ...................................................5
The last 100 million years.......................................................... 9
Environmental change .........................................................................9
Adaptive radiation of marsupials ............................................. 13
Origin of marsupials ...........................................................................15
Origin and radiation of monotremes ........................................ 16
The megafauna ....................................................................... 18
Additional resources................................................................ 21
Suggested answers................................................................. 25
Exercises – Part 3 ................................................................... 27
Part 3: Changing environments and biota in Australia
1
Introduction
In Part 2 of this module you became familiar with the theory of plate
tectonics and saw how it is related to the biota found on the separate
continents which made up Gondwanaland (Gondwana), especially the
Australian continent. In this part of the module the nature of changing
environments during the northerly drift of Australia and the resultant
effects on the evolution of ancient and modern flora and fauna
are discussed.
Most emphasis is given to the marsupial and monotreme mammals, as
they are typically Australian biota. Although a large number of
marsupial species also occurs in South America, the species are mainly
very different from the Australian marsupials. Monotreme fossils have
also been found in South America, but living monotremes are restricted
in their distribution to Australia and New Guinea and most fossil
monotremes have been found here.
In this part of the module you will need to read and work carefully
through the material provided, to practice important skills especially
gathering, processing and analysing information from secondary sources.
This means that you need to be able to research reference material,
understand it and present conclusions based on your research.
If you have access to a library, CD ROM or the Internet, you can read
further than the material provided here. However, there is sufficient
research information in the material provided for you to carry out the
exercises and assignments and to achieve the competencies required.
In Part 3 you will be given opportunities to learn to:
2
•
discuss current research into the evolutionary relationships between
extinct species, including megafauna and extant Australian species
•
identify and describe evidence of changing environments in
Australia over millions of years
•
identify changes in the distribution of Australian species, as
rainforests contracted and sclerophyll communities and grasslands
spread, as indicated by fossil evidence
Evolution of Australian biota
•
discuss current theories that provide a model for these changes.
In Part 3 you will be given opportunities to:
•
gather information from secondary sources to describe some
Australian fossils, where these fossils were found and use available
evidence to explain how they contribute to the development of
understanding about the evolution of species in Australia.
•
perform a first-hand investigation, gather information of named
Australian fossil samples and use available evidence to identify
similarities and differences between current and extinct Australian
life forms.
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. Revised November 2002. The most up-to-date version can be
found on the Board's website at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html
Part 3: Changing environments and biota in Australia
3
Geological time scale and biota
As you saw in Part 2, Australia was once part of the huge landmass of
Pangaea and then of the southern supercontinent, Gondwanaland
(Gondwana). Even before Gondwana split from Pangaea most of the
major groups of plants and animals known today existed on the Earth.
Although the fossil record shows that mammals, birds and probably the
flowering plants had not yet risen to any prominence by the time
Gondwana separated from the rest of the Pangaean landmass.
The table in the Additional resources shows the categories of geological
time for the Earth but these are not drawn to scale. All periods are shown
as fairly similar sized boxes, but the time span of each period is given,
along with the major plant and animal groups from each. The table also
indicates when it is thought each group evolved, reached prominence in
the fossil or living record and when some became extinct.
You should not be concerned if other sources do not match exactly the
one given in the table which has actually been constructed from several
sources of information.
The generally accepted progression of evolution, as deduced by various
types of information (especially fossil evidence), will be the same or very
similar in most of these sources. However, you may find small
discrepancies. These may be due to differences in opinion or
interpretation by authors or even to how recently the source has been
written or updated.
In Part 2 you saw that Australia’s association, firstly with the other land
areas making up Pangaea, and then those bound up into Gondwana,
resulted in the biota of the modern Australian continent showing some
similarities to those of other areas of the world.
However, after its rifting from Antarctica and its movement north with
the drifting of the Indo-Australian Plate, Australia experienced
considerable changes in both climate, geography and geology so that
species of organisms which were present on the continent were isolated
4
Evolution of Australian biota
and exposed to different natural selection pressures, so that they changed
and evolved into the groups of organisms present today.
The mechanisms of this speciation and adaptive radiation were
discussed in detail in Part 1. If you need to, return briefly to your notes
and assignments from Part 1 just to make yourself familiar again with
these mechanisms and how they are thought to work.
Evidence of changing environments
No one was around to witness the changes occurring in world
environments, but a good deal of information on palaeogeography
(pre-human geography) and palaeoclimatology (pre-human climate) can
be obtained by a variety of methods including:
•
fossils
•
tree rings
•
dating methods and
•
glaciers.
Fossils
The remains of organisms can be preserved in a number of ways,
including:
•
the preservation of bodies or body parts in amber (gum), peat or tar
where bacteria are prevented from breaking down the organic
material
•
replacement of body tissues by minerals (eg. opal)
•
impressions in mud which subsequently turns to rock
•
the preservation of whole organisms in ice (eg. woolly mammoth).
These fossils often give clues about the environment or climate.
For example, finding the fossil remains of marsupials which had
skeletons adapted for climbing and teeth adapted for feeding on leaves
and fruits suggest that the area in which they lived at the time was
probably a forest, not a shrubland or grassland.
Part 3: Changing environments and biota in Australia
5
A fossilised trilobite indicates a past marine environment.
(Photo: © LMP Tim Reid).
If fossilised leaves of rainforest species were also found it might indicate
that the region was part of a rainforest rather than a sclerophyll forest.
Similarly, the finding of fossils of fish, turtles and frogs would indicate
an aquatic rather than a terrestrial environment. Pollen and spores from
plants can be quite distinctive and are frequently used to deduce the
nature of the past vegetation in an area.
Tree rings
Tree rings represent seasonal growth cycles. This means that the ages of
trees can often be calculated. The rates of growth each season can also
be estimated from tree rings.
Various environmental factors, including rainfall, aspect (sunshine) and
altitude can affect tree growth. In this way the study of tree rings can
indicate climate and geography of the place where a tree grows, or where
its fossil remains are found.
6
Evolution of Australian biota
Petrified wood from the Permian showing large annual growth rings.
This indicates that there were warm conditions at the time that this tree grew.
(Fossil Andrew West). (Photo: © LMP Thomas Brown)
Dating methods
The age of rocks which contain radioactive minerals can be determined
by calculating backwards from the amount of the radioactive element
remaining in the rock and the amount of the element into which it decays
(changes). For example uranium-235 decays into lead-207.
The rate at which radioactive decay occurs is fixed and is known as the
half-life of the element. That is, the time taken for half of the original
element present (parent element) to decay into the other element
(daughter element). In the case of uranium-235 changing into lead-207,
the half-life is 713 million years. This method is called
radiometric dating.
If fossils, or the rocks in which they are found, can be given a date of
formation, then other fossils and rocks can be dated relative to them.
If they are found higher in layers (strata) of the Earth, then they must
have been formed later and so are younger, while lower ones are older.
Once a fossil type has been dated, then it can be used to establish the
dates of other fossils found with it. This is called relative dating.
There can be problems with the method of relative dating, as it is known
that the positions of rock strata can move in various ways, so that the
younger fossils or rocks may be found under rather than above older
Part 3: Changing environments and biota in Australia
7
ones. However, other geological evidence can often identify this
disruption to the layering.
Glaciers
As the ice sheets of glaciers move over the surface of the Earth they
erode rocks and deposit material in a characteristic way. During ice ages
glaciers advance and then retreat during warmer periods.
Studying the occurrence of features of glacial erosion can enable
scientists to map glaciers and determine a good deal about the climate of
the time.
Ice cores
Cores of ice taken from glaciers and from polar ice caps can also be used
to determine climate. The higher levels of carbon dioxide in air bubbles
trapped in ice can indicate greenhouse global warming. Ash trapped in
ice can show the presence of volcanic activity at the time the ice was
formed. In an ice core the most recently formed ice is at the top and the
older at the bottom.
Complete Exercise 3.1 now.
8
Evolution of Australian biota
The last 100 million years
Environmental change
In this section you will become more familiar with the sequence of
changes in geography, climate and vegetation of Australia prior to its
separation from Gondwana and during its drift northward towards
south- east Asia. It was these environmental changes which almost
certainly gave rise to the evolution of the diverse flora and fauna of
this continent.
The information that follows outlines the changes in climate and vegetation
during different periods in Australia. You will be using this information to
complete a table to summarise these changes.
Cretaceous period
The beginning of this period in Australia was cold. The sea level was
high and much of the land mass consisted of islands in a shallow inland
sea. The vegetation was dominated by non-flowering vascular seed
plants (conifers, cycads, horse tails and seed ferns) but the first flowering
plant fossils also appeared during this period.
The climate warmed later in the Cretaceous, the land of Australia was
uplifted and the angiosperms began to dominate the vegetation.
By the end of the period mass extinctions, which included the Australian
dinosaurs, occurred. This was possibly due to a cooling effect brought
about by the collision of an asteroid with the Earth. This is thought to
have caused dust in the atmosphere and a resulting reduction in the
heating of the Earth’s surface by heat from the Sun.
Part 3: Changing environments and biota in Australia
9
Paleocene-Eocene periods
Australia had broken away from Antarctica by about the end of the
Eocene period and began drifting north. Australia’s climate went from
being wet and warm to being cool. Large inland lakes were part of the
landscape and rainforests covered much of the continent. Ferns and
conifers were still found, but flowering plants were certainly the
dominant land plants, including species belonging to the genus
Nothofagus or southern beech trees (see Part 2).
Oligocene period
This period was also cold and wet in Australia. Rainforests, including
Nothofagus trees, dominated and swamps were common. The first
Eucalyptus trees appeared during this period.
Miocene period
In the early Miocene period sea levels varied and the climate fluctuated
between being hot and cold. But, it was always wet and rainforests were
still dominant. However, by the late Miocene sea levels fell and the
climate was cold and was becoming drier. Rainforests were beginning to
give way to forests of trees with hard dry leaves (sclerophyll), especially
Eucalyptus species, which could tolerate the drier conditions.
Casuarina or she oak species of trees and shrubs were also common
angiosperms of this later period.
Pliocene period
This was a time of raised sea levels with rainforests present in the wet
conditions at the beginning of the period, but giving rise to sclerophyll
forest, woodland and even grasslands later, especially in inland Australia.
Pleistocene period
Both temperatures and sea levels fluctuated during the Pleistocene, as
Australia experienced alternating icehouse and greenhouse conditions.
However, in general the climate became more arid and plants and
animals able to cope with such conditions evolved. The giant forms,
often called the megafauna evolved early in this period but became
extinct by the end of it.
10
Evolution of Australian biota
The table below uses a format similar to the table in the Additional
resources showing the Earth’s geological time periods. Some of the
information in the table has been filled in but you will need to carefully read
the descriptions given for each period. Complete the worksheet.
Period
Time span
(million years)
Early Cretaceous
146-97
Late Cretaceous
97-65
PaleoceneEocene
Geography
Climate
Vegetation
islands in shallow
inland seas
cold, moist
cycads and conifers,
horsetails and seed
ferns
rainforests containing
ferns and conifers but
mainly angiosperms,
especially Nothofagus
(southern beech
trees)
rifting from
Antarctica began;
large inland lakes;
northern drift of
Australia
first Eucalyptus trees
Oligocene
Early Miocene
Late Miocene
10.5-5
Pliocene
Pleistocene
Recent (holocene)
arid inland,
north dominated
by summer
rainfall and
south by winter
rainfall.;
temperatures
increase from
south to north
Check your answers.
Part 3: Changing environments and biota in Australia
11
The environmental conditions of Australia varied considerably as the
continent moved north, but the most notable trend in the last 15 million
years was one of increasing arid conditions. The overall change in the
climate and vegetation from being cool, wet and forested to being warm
and with dry mainly woodland, shrubland and grassland ecosystems.
Climate
warm and dry
cool and wet
15
10
5
today
Time (millions of years from present)
Climate change in Australia over the past 15 million years. The dark shading
shows the increase in warmer and drier conditions.
You will draw on this information in the next part when you will
examine vegetation patterns and the impact on Australian biota
over time.
Complete Exercise 3.2.
12
Evolution of Australian biota
Adaptive radiation of marsupials
The changes in environments and vegetation in parts of Australia led to
the evolution of very different animals under the influence of different
selection pressures. The first marsupial mammals are thought to have
come from South America. The likely ancestor of Australian marsupials
was probably a small species like the small South American marsupial
called Dromiciops australis, which is found in the beech forests of
southern Chile. This animal has many features like the small possums
of Australia.
Dromiciops australis a South American marsupial which is thought to belong to
the group (Microbiotherids) from which Australian marsupials evolved.
(Photo: © LMP T R Grant)
This species is quite similar in appearance to the Australian eastern
pygmy possum (Cercartetus nanus). All other American marsupials
have sperm which are attached together in pairs, while Dromiciops
australis and the Australian species have single sperm. There is also
considerable similarity in the DNA between this little creature and
Part 3: Changing environments and biota in Australia
13
Australian marsupials. Dromiciops itself is not the actual ancestor but
may belong to the same ancestral group as the original Australian
marsupials. Once such a marsupial ancestor (or ancestors) reached
Australia via Antarctica, the group radiated by adaptation to the different
environments of the continent to produce the range of unique marsupials
found in Australia today.
Despite what some books say, there are still lots of species of marsupials
in South and Central America today (around 75 species).
American marsupials are called opossums, which are completely
different from the Australian group of marsupials which are called
possums. One species is found in North America, but it almost certainly
moved there quite recently in geological terms. There are no kangaroos,
wombats, koalas or bandicoots on the American continent, and most
American marsupials are fairly small creatures, the largest of which is
about the size of the Australian brushtail possum.
During the adaptive radiation of marsupials in Australia a number of
species became extinct as conditions changed. There were presumably
no variations within their populations which allowed these marsupials to
survive the changes.
The major groups of modern Australian marsupials are summarised in
the table below. Adaptation to different habitats has occurred during
their evolution and the varied diets of some are shown in the table.
Order
Common names
Example
Diet
Dasyuromorphia
dasyurids
carnivores
Peramelemorphia
bandicoots
marsupial ‘mice’
Tasmanian devil native
‘cats’
bandicoots
bilby
Diprotodontia
•
koala
•
koala
•
leaf eater
•
wombats
•
common wombat
•
grazer
•
macropods (kangaroos,
wallabies, potoroos,
bettongs, rat-kangaroos)
•
grey kangaroo
•
grazer
•
swamp wallaby
•
browser
•
brush-tailed bettong
•
fungus, seed, tuber
and insect eater
•
tree kangaroo
•
leaf and fruit eater
•
possums
•
ringtail possum,
brushtail possum
•
leaves, flowers, fruit
eaters
•
pygmy possums
•
eastern pygmy
possum
•
nectar, pollen eater
•
gliders
•
sugar glider
nectar, pollen, insect,
sap eater
•
14
insectivores
Evolution of Australian biota
Optional
You could try to use either the Internet, CD ROMs or go to your local
library and have a look at pictures of the members of these groups of
marsupials. Find out what they look like, what they eat and where they
are found.
Origin of marsupials
As was mentioned earlier, the currently most accepted theory of the
origin of the Australian marsupials is that their ancestors came from
South America, probably around 65-55 mya in the late Cretaceous or
early Paleocene period. If this was a reasonable theory, then the
following might be reasonable expectations (hypotheses) from
the theory.
∑
There should be older marsupial fossils in south America than in
Australia.
∑
Marsupial fossils should be found in Antarctica
∑
At least some South American marsupials should show affinities
(similar characteristics) with Australian species.
Most modern South American marsupials appear to be more closely
related to the earliest marsupial fossils which were found in the
Cretaceous period in North America (around 100 mya) than to modern
Australian marsupials. The ancestors of the modern South American
forms quickly disappeared from the north of their range, but their
descendants persisted in South and Central America during the
Cretaceous period. It should be noted that the one species of marsupial
now found in North America, the Virginian opossum, has more recently
invaded from Central America.
A marsupial fossil has been found on an island off the Antarctic
Peninsula, adjacent to the tip of South America. The living species
Dromiciops australis has DNA similarities to Australian marsupials.
Dromiciops australis has unpaired sperm, while the sperm of all other
American forms swim together in pairs. These pieces of evidence
suggest that the theory has at least some support.
An alternative theory that the marsupial ancestors entered Australia from
the north has little support, as no marsupial fossils have yet been found in
Asia. It was not until around 15 mya that Australia was close enough to
south-east Asia for mammals to have reached the mainland from
the north.
Part 3: Changing environments and biota in Australia
15
Origin and radiation of monotremes
Monotremes are mammals which lay eggs but, like all other mammals,
feed their young on milk. There are currently only three living species of
the Monotremata group, two species of echidnas (or spiny anteaters) and
one species of platypus. The short-beaked echidna occurs both in
Australia and Papua New Guinea; the long-beaked echidna occurs only
in Papua New Guinea; the platypus occurs only in Australia.
There was once a greater abundance and distribution of monotreme
species in Australia than currently occurs. Fossils of this group show
that it has been here for longer than the marsupials. The oldest
monotreme fossils are from the Lightning Ridge area in western
New South Wales. These appeared to have been from platypus-like
species which had teeth possibly adapted for eating crustaceans
(eg. shrimps, crayfish). It would seem then that they were probably
aquatic, so that during the Cretaceous period in which they occurred
(around 110-115 mya) the environment of the Lightning Ridge area
would have been much wetter than it is today.
Until recently monotreme fossils had only been found in Australia, but in
1991 and 1992 several fossil monotreme teeth (which are quite
distinctive) were found in Patagonia in the south of Argentina.
These were about 62 million years old. Can you remember in which
geological period that date falls? No doubt you would have decided the
Paleocene period.
Fossils of three ancient species of platypuses have been found that are
from 15-23 million years old. A number of fossil echidnas have also
been found on mainland Australia, indicating greater species abundance
and distribution of the group.
The early age of monotreme fossils, the greater abundance of fossil
forms, and the occurrence of living forms in Australia has led some
palaeontologists to hypothesise that the group may have evolved in
Australia, before it broke away from Antarctica, and that the South
American forms descended from an Australian ancestor. At present there
are insufficient data to support or reject this hypothesis.
16
Evolution of Australian biota
Answer the following questions, then check your answers at the end of
this part.
1
The most accepted theory is that Australian marsupials evolved from
ancestors which originally dispersed here from south America.
Discuss the evidence which supports this theory.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
2
On the other hand it has been suggested that the fossil monotreme
species found in South America may have evolved from an
Australian ancestor. Briefly describe evidence for such a suggestion
and comment on its acceptance by palaeontologists.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Check your answers.
Complete Exercise 3.3 where you will be comparing a fossil form of a
platypus to a current form.
Part 3: Changing environments and biota in Australia
17
The megafauna
Gigantism occurred in mammal groups in many parts of the world during
the Pleistocene period and those in Australia were no exception.
The term megafauna refers primarily to large marsupials, such as giant
kangaroos (eg. Procoptodon goliah, Macropus giganteus titan) and huge
four legged herbivores (eg. Diprotodon optatum, Zygomaturus trilobus).
There were also very large echidnas (eg. Zaglossus hacketti) and a few
large carnivores, like the marsupial lion (Thylacoleo carnifex).
As well, there were also known to be at least four giant reptiles,
including a goanna and constrictor snake, several carnivorous birds and a
horned land tortoise.
During this period such large forms co-existed with smaller species of
the same groups and all the giant forms had died out before the end of the
period (about 10 000 years ago.)
Several suggestions have been made to explain the selection pressure
acting on ancestral populations to favour large size. The most common
suggestions are outlined below.
The climate during the Pleistocene period was often very cold and so the
small surface area to volume ratio of large animals which regulated their
body temperature would reduce body heat loss and increase survival.
In Australia, soils were often poor in nutrients and so plant growth may
have been low and food of poor quality (more indigestible).
Large digestive systems, especially those with fermentation chambers
full of micro–organisms, could be carried by large animals, allowing
them to make use of the poor quality of vegetation available. Along with
this, the large animals would also lose less body heat and therefore,
require less food anyway.
However, there were also large reptiles (which probably did not regulate
their body temperature) at the time. The climate during the Pleistocene
was not always cold and similar, small species also successfully survived
and reproduced during the period. These things all highlight the
18
Evolution of Australian biota
difficulties of research into the environments, flora and fauna of
Australia in the past.
Australian megafauna. Drawings of hypothetical reconstructions of some
Australian megafauna species. A species of giant kangaroo is shown along
with a species of giant herbivorous diprotodont. The human is included for a
size reference.
There is also controversy over the reason for the demise of the
megafauna. Some scientists maintain that they were hunted and killed
by Aboriginal peoples, who were in Australia by between
40-60 000 years ago, or that Aboriginal use of fire eventually changed
the vegetation and brought about their extinction. Another theory is that
humans killed off the megafauna and this resulted in a change in the
vegetation. As large herbivores were no longer eating the vegetation,
very intense bushfires occurred due to the accumulation of fuel.
The Aboriginal peoples were thought to have subsequently adjusted the
situation by regular burning, maintaining grasslands and woodlands,
where forests had occurred previously.
Again, because history was not recorded at the time, the theories are
based on indirect evidence, some of which is highly speculative.
Many botanists believe that the vegetation changed as a result of climate
change and it seems that no one really knows why the megafauna died
out in Australia.
As part of your syllabus requirements you are asked to gather information
from secondary sources to describe some Australian fossils, where these
fossils were found and use available evidence to explain how they
contribute to the development of understanding about the evolution of
species in Australia.
Part 3: Changing environments and biota in Australia
19
If you visit the LMP Science online website there are some good starting
points for your investigation.
http://www.lmpc.edu.au/science
Below are some famous Australian fossil locations that you could use as
a basis for your research.
Riversleigh
Bluff Downs
Murgon
Lightning Ridge
Naracoote
Canowindra
Choose two of these sites, describe two fossils found at the site and give
the age of the fossils. If possible say how each fossil contributes to the
development of understanding. Some examples are given in the
Additional resources section.
Write your answers to the above in Exercise 3.4.
20
Evolution of Australian biota
Additional resources
Geological time
Era
Period
Epoch
Time spans
(million
years)
Cenozoic
Quaternary
Recent
(Holocene)
Pleistocene
10 000-today
2 mill-10 000
Tertiary
Pliocene
Miocene
Oligocene
5-2
25-5
40-25
Australia
drifts north
(35-45 mya)
55-40
65-55
dominance of
land dominated
flowering plants by mammals and
(Angiosperms) bird
Cretaceous
140-65
Gondwana
begins to rift
(approx. 150
mya)
major
extinctions
flowering plants
expand nonflowering seed
plants (eg.
conifers,
cycads, seed
ferns) decline
major extinctions
last dinosaurs
adaptive radiation
of insects
Jurassic
210-140
Pangaea rift
(approx. 170
mya)
angiosperms
evolve nonflowering seed
plants
dominant
age of dinosaurs,
first birds
Eocene
Paleocene
Mesozoic
Part 3: Changing environments and biota in Australia
Plant life
Animal life
first Homo
sapiens,
megafauna
21
Paleozoic
Paleozoic
Proterozoi
c
Triassic
250-210
non-flowering
seed plants
dominant
first mammals
first dinosaurs
Permian
300-250
major
extinctions,
especially
primitive plants
expansion of
reptiles major
extinctions,
especially
amphibians and
trilobites
Carboniferous
360-300
primitive land
plants then
non-flowering
seed plants
and ferns
dominant
age of
amphibians first
reptiles first insect
radiation
Devonian
410-360
dominance of
primitive
vascular plants
first seed
plants
age of fishes first
amphibians first
insects
Silurian
440-410
first vascular
land plants
adaptive radiation
of fishes
Ordovician
500-440
marine algae
abundant
first land
arthropods
Cambrian
550-500
marine algae
cyanobacteria
first fish
most invertebrate
phyla known
today
Neoproterozoic
1,000-550
cyanobacteria
early cnidaria,
annelids,
arthropods and
echinoderms
Mesoproterozoi
c
1 600-1 000
cyanobacteria
first animals
Paleoproterozo
ic
Archaean
22
2 500-1 600 cyanobacteria
atmosphere
rich in oxygen
4 500-2 500
Evolution of Australian biota
Australian fossils
Riversleigh
Thylacine
The Thylacine or Tasmanian tiger became extinct in the 1930’s.
The fossils at Riversleigh show that the animal was not restricted to
Tasmania but used to live on the mainland of Australia. The fossils also
show that there was more than one type of thylacine. This information
came too late to save this organism from extinction but it does show that
the remnant species in Tasmania should have been preserved.
Thingodonta
This fossil marsupial is from the Miocene period. It is unlike any
living marsupial. It lived in the rainforest and may have eaten
caterpillars or eggs.
Canowindra
Fish fossils
A chance discovery during road works exposed the rich Canowindra fish
fossils. The first find contained the complete fossils of 100 fish from the
late Devonian. There were four types of fish present. Three of these
were armoured fish and the fourth was an air-breathing lungfish.
Naracoote cave
Marsupial lion
The marsupial lion was part of the Australian megafauna. It was the
largest marsupial carnivore to live in Australia. It would have
hunted other members of the megafauna such as Diprotodon during
the Pleistocene.
Giant short faced kangaroo
This animal lived during the Pleistocene. It was up to 3 metres in height.
It was double the size of the largest kangaroos living today. It had front
paws that were like hooks. Its back legs had one toe.
Part 3: Changing environments and biota in Australia
23
The Naracoote fossil site included the period when humans first arrived
in Australia. The climate was changing becoming increasing cooler and
drier. There were however, periods of warmer wetter climate
corresponding to the glacial and interglacial periods.
If you are interested in reading more about the changing environments
and palaeontology of Australia the following books are a good place to
start. Be warned that some are extremely detailed making the text
difficult to read, but all have great pictures and are interesting to skim
through to see pictures of fossils and reconstructions of fossil species.
Long, Vickers-Rich and Rich and White also present information on
plate tectonics with good coloured illustrations.
24
•
Archer, M, Hand, S and Godthelp, H. 1986. Uncovering Australia’s
Dreamtime. Surrey Beatty and Son, Sydney.
•
Archer, M, Hand, S and Godthelp, H. 1996. Riversleigh. The Story of
Animals in Ancient Rainforests of Inland Australia. Reed, Sydney.
•
Augee, M and Fox, M. 1999. The Biology of Australia and New
Zealand. Pearson Education, Sydney.
•
Gould, E and McKay, G. 1998. Encyclopedia of Mammals 2nd
Edition. Weldon Owen, Sydney.
•
Long, J A. 1998. Dinosaurs of Australia and New Zealand and
Other Animals of the Mesozoic Era. NSW University Press, Sydney.
•
MacDonald, D. 1984. The Encyclopaedia of Mammals. Volume 2.
George Allen and Unwin, London.
•
Strahan, R. 1995. The Mammals of Australia. Reed Books, Sydney.
•
Vickers-Rich, P. and Rich, H T. 1993. Wildlife of Gondwana. Reed,
Sydney.
•
White, M. 1994. The Greening of Gondwana. Reed, Sydney.
•
White, M. 1994. After the Greening. The Browning of Australia.
Kangaroo Press,
Evolution of Australian biota
Suggested answers
Environmental change
Period
Time span
Geography
(million years)
Climate
Vegetation
islands in shallow
inland seas
cold, moist
cycads and
conifers, horsetails
and seed ferns; first
flowering plants
Early Cretaceous
140-97
Late Cretaceous
97-65
Paleocene-Eocene
65-40
rifting from
Antarctica began;
large inland lakes;
northern drift of
Australia
cool
rainforests
containing ferns and
conifers but mainly
angiosperms,
especially
Nothofagus
(southern beech
trees)
Oligocene
40-25
swamp
cold, wet
first Eucalyptus
trees rainforests
with Nothofagus
Early Miocene
25-10.5
sea levels varied
hot and cold
fluctuations
rainforests dominant
Late Miocene
10.5-5
sea levels fell
cold, dry
reduction of
rainforests.
Sclerophyll forests
increasing
casuarina species
raised sea levels
wet
rainforests then
sclerophyll forests
woodlands and
grasslands
Pliocene
5-2
Part 3: Changing environments and biota in Australia
25
Pleistocene
2 million-10000
Recent (holocene)
10 000-today
temperature and
sea levels
fluctuated
alternating
icehouse and
greenhouse
conditions, more
arid
arid inland, north
dominated by
summer rainfall
and south by
winter rainfall.
Woodland,
grassland and
shrubland
temperatures
increase from
south to north
Origin and radiation of the monotremes
26
1
South American marsupial fossils are older than those in Australia.
There has been a marsupial fossil found in Antarctica and the living
species Dromiciops australis has DNA and sperm similarities to
Australian marsupials. These pieces of evidence all give support to
the theory.
2
A greater diversity and older monotreme fossils have been found in
Australia than in south America. However, the numbers of fossils
found so far are quite low and so there are not really enough data yet
to support this theory.
Evolution of Australian biota
Exercises - Part 3
Exercises 3.1 to 3.4
Name: _________________________________
Exercise 3.1: Evidence of changing environments
Identify and describe three sources of evidence for the changing
environment in Australia over time.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Part 3: Changing environments and biota in Australia
27
Exercise 3.2: The last 100 million years
Describe the general trend in the vegetation of Australia form the nonflowering seed plants in the Cretaceous through to today.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Exercise 3.3: Comparison between a fossil and living
species of the same group.
The two photographs following show the upper skull of a 15 million year
old fossil platypus (Obdurodon dicksoni) and the modern platypus
(Ornithorhynchus anatinus) taken from the top (dorsal view) and the
bottom (ventral view).
In the modern platypus the teeth are lost in the adult and replaced by
horny grinding pads made up of material a bit like fingernail (one of
these is seen in the ventral view picture). These pads are worn away
as the food is ground up but they are continuously replaced. The fossil
species has teeth, although some are missing in the specimen in
the photograph.
Reconstructions of the whole skulls of the fossil and modern platypuses
showing the whole tooth arrangement are shown on the next page.
28
Evolution of Australian biota
A: Ventral view
B: Dorsal view
Skulls of the extinct fossil Miocene (15 million years old) platypus, Obdurodon
dicksoni (top skull), and the modern platypus, Ornithorhynchus anatinus
(bottom skull). (Source: Grant, T. 1995. The Platypus. A unique mammal.
NSW University Press, Sydney. Plates 14 and 15)
A View from below (ventral) - the sockets for the back teeth are seen in
the fossil skull. One horny grinding pad is in place (upper side; dark
in colour) in the modern skull. The other is missing but shows the
empty socket where the juvenile teeth have been lost.
B View from the top (dorsal). In both views the long bones extending
forward of the brain case support(ed) the bill.
Part 3: Changing environments and biota in Australia
29
Drawings made of the fossil (left side) and modern (right side) platypus skulls to
include all of the features of the skulls and to show the complete set of teeth in
the fossil form (X) and grinding plates in the modern skull (Y).
In each drawing the views in a clockwise order are dorsal (upper), ventral
(lower) and lateral (side) views.
(Source: Musser, A M. and Archer, M. 1998. New information about the skull
and dentary of the Miocene platypus Obdurodon dicksoni, a discussion of
ornithorhynchid relationships. Philosophical Transactions of the Royal Society
of London B 353)
a) Describe the similarities between the two skulls.
______________________________________________________
______________________________________________________
______________________________________________________
b) Describe the differences between the two skulls.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
30
Evolution of Australian biota
c) Changes from the ancestor of Obdurodon dicksoni and
Ornithorhynchus anatinus have come about as a result of natural
selection acting on variations during the evolution of the two species.
i)
Suggest possible reasons for both having the similarities you
described in the skulls of the two species.
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
ii)
Suggest possible changes to the species’ environments which
could have resulted in the evolution of the differences in the
skulls which you described.
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
Exercise 3.4: Named Australian fossils
Name of fossil site 1: _______________________________________
Description and age of fossil 1 ________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Part 3: Changing environments and biota in Australia
31
Description and age of fossil 2 _________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Name of fossil site 2:________________________________________
Description and age of fossil 3 _________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Description and age of fossil 4 _________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
32
Evolution of Australian biota
Gill Sans Bold
Biology
Preliminary Course
Stage 6
Evolution of Australian biota
Part 4: Adaptations to the Australian environment
0
0
2
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to T S
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in D M
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a
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or AM
c
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2
Contents
Introduction ............................................................................... 2
The Australian environment ...................................................... 3
Climatic regions....................................................................................3
Biodiversity................................................................................ 6
The need to maintain biodiversity........................................................7
A current effort to monitor biodiversity ..............................................10
Technological science ............................................................. 11
Discovery of the platypus...................................................................11
Contributions of new technology .......................................................15
Additional resources................................................................ 17
Suggested answers................................................................. 19
Exercises – Part 4 ................................................................... 21
Part 4: Adaptations to the Australian environment
1
Introduction
You will recall that environments have changed with tectonic movements
and changes in global climate. In this part you will describe the main
features of major Australian environments in terms of variations in
temperature and availability of water.
Biodiversity is talked about a lot in the media but what is it exactly? In this
part you will discuss changing ideas of scientists in the last 200 years about
Australian species as a result of new information and technology.
In this part you will be given opportunities to learn to:
•
identify areas within Australia that experience significant variations in
temperature and water availability
•
explain the need to maintain biodiversity
In this part you will be given opportunities to:
•
process information to discuss a current effort to monitor biodiversity
•
identify data sources, gather, process and analyse information from
secondary sources and use available evidence to illustrate the changing
ideas of scientists in the last 200 years about individual species such as
the platypus as new information and technologies became available.
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally issued
1999. Revised November 2002. The most up-to-date version can be found on the
Board's website at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html
2
Evolution of Australian biota
The Australian environment
As the Indian-Australian crustal plate moved north, after the break up of
Gondwana, the climate of Australia alternated between being cool and dry
(icehouse conditions) to being warm and moist (greenhouse conditions).
However, by the end of the middle Miocene period (24 mya) the continent
was undergoing increasing aridity and by the Pleistocene (1.8 mya) the
climate appeared to have been much as it is today, perhaps even a little drier
and certainly cooler.
As discussed in Part 3, during these periods of geological and climatic
changes new species evolved while others became extinct, resulting in the
present day fauna and flora. Many species of plants and animals are
adapted to dry environments but also to environments with extremes of
temperature (central and alpine areas) and often low soil nutrient levels,
high salinity and frequent exposure to fire.
Climatic regions
In terms of temperature, the climate of Australia becomes cooler from north
to south and the extremes of temperature increase from the coast to the
centre of the continent. Annual rainfall is highest in Tasmania, the east
coast of the mainland and in northern tropical Australia, although this
northern part of the continent experiences dry winters and very wet
summers (wet season). The pattern of rainfall for the central arid areas of
Australia is long periods of drought followed by flooding rain. In Alice
Springs there may be zero rainfall for most months of the year with all of
the rain falling in summer. The following maps show the major rainfall
patterns and the temperature zones in Australia.
Part 4: Adaptations to the Australian environment
3
Average summer (January) and winter (July) temperatures in Australia.
Note that darker shading shows higher temperatures in summer and lower
in winter.
(Source: Australians and the environment, AUSLIG, Australian Bureau of Statistics
ABS Catalogue No 4601.0. 1992. ‘Commonwealth of Australia copyright
reproduced by permission’.)
Average summer (January) and winter (July) rainfall in Australia. The position of
the Great Dividing Range is also drawn on this map as a dashed line. Above the
solid line, rainfall is mainly in summer; below the line, it is mainly in the winter.
(Source: Australians and the environment, AUSLIG, Australian Bureau of Statistics
ABS Catalogue No 4601.0. 1992. ‘Commonwealth of Australia copyright
reproduced by permission’.)
In the inland areas of Australia there is a great variation in daily
temperatures. In the winter daytime temperatures may be 20 ºC while at
night the temperature falls to below zero.
Australia is the driest continent on Earth (except for Antarctica), with more
than half of the continent considered to be arid. Less water runs off from
the Australian landscape in streams and rivers than on any other continent
4
Evolution of Australian biota
and 90% of the rain which falls is lost by evaporation. In spite of these arid
areas being very hot and very dry there are a range of climates in Australia,
including some which are extremely wet in summer (tropical north) and
extremely cold in winter (alpine and central Australia.)
Use the previous information to complete the following questions.
1
The hottest and most arid areas of Australia are:
A) in the far north nearest the equator
B) in central and central western Australia
C) in Tasmania and southern Western Australia
D) along the east coast of Australia.
2
A traveller to northern Australia around Darwin was amazed to find
that there was no tropical rainforest although the heat and humidity
indicates that this was definitely in a tropical area. The main reason
for this is that:
A) northern Australia is not close enough to the equator to have
rainforest
B) the soils are too poor to support rain forest
C) there is not enough rain in the winter for the needs of rainforest
D) all of the rainforest has been cut down by humans
3
A plant or animal found living in central Australia would need to be
adapted to cope with the following climatic conditions.
A) high rainfall and constant high temperatures
B) low rainfall, hot summer temperatures and cold winter
temperatures
C) low rainfall and hot temperatures all of the time
D
4
high rainfall in the summer but low in the winter and a wide
range of temperatures from summer to winter
Use the maps provided in the materials to describe the
temperature and rainfall you would expect to find in north
Queensland on the coast.
_____________________________________________________
_____________________________________________________
_____________________________________________________
Check your answers.
Complete Exercise 4.1 now.
Part 4: Adaptations to the Australian environment
5
Biodiversity
Much has been said and written about biodiversity. If you listen to the news
or read the papers there seems to be constant reference to biodiversity.
But what is it?
What is biodiversity?
Biodiversity can be defined as the variety of life forms: the plants, animals
and micro-organisms found in an area. But it is more than just the living
things. According to the National Strategy for the conservation of
Australia’s Biological Diversity, biodiversity has been defined as:
the variety of life forms; the different plants, animals and
microorganisms, the genes they contain, and the ecosystems they form. It
is usually considered at three levels; genetic diversity, species diversity
and ecosystem diversity.
So a definition of biodiversity should incorporate these three levels:
•
genetic diversity
•
species diversity
•
ecosystem diversity.
Genetic diversity
The natural variety within a population gives it a robustness to survive
changing conditions. It is important to maintain genetic diversity as a
safeguard against new pests and environmental change. Wild species of
domesticated crops contain a large natural gene pool which should be
maintained for the genetic diversity of the future. This natural genetic
diversity should be valued for future breeding in changing
environmental conditions.
6
Evolution of Australian biota
For a population to be viable, the organisms in it must share a large gene
pool. It is possible to have many individual members of a species living in
an area but still have reduced genetic diversity. If a population were
reduced to having only a few members of a species, this would greatly
reduce the gene pool for the species. If large numbers of individuals were
then bred from just these few organisms, you would have an overall
decrease in genetic diversity. This leads to a lack of genetic vigour,
or strength.
Species diversity
This is the most common usage of the term biodiversity. Species diversity
is the number of different species in an area or ecosystem and their
abundance. This means having lots of different species, and within each
species, having many members present at a certain time.
Ecosystem diversity
Ecosystems are a combination of biotic and abiotic factors interacting
together in an environment in a self-sustaining manner. Many ecosystems
that are resistant to human impact show a high level of biodiversity.
Ecosystem diversity is having a number of different ecosystems in an area.
For example, a national park may show biodiversity by containing
rainforest, heathland and grassland.
The need to maintain biodiversity
As human activity continues to spread to the furthest corners of Earth,
natural areas are changed and modified, resulting in increasing and
widespread extinctions of species. Currently, many experts believe
such extinctions are occurring at the fastest rate in human history.
This is perhaps the fastest rate since the extinction of dinosaurs 65 million
years ago.
This loss of Earth’s biological diversity is said to be rapidly accelerating as
desertification, deforestation (especially in the tropics), degradation of
oceans and water resources, atmospheric change and other environmental
changes continue at a rapid pace.
Part 4: Adaptations to the Australian environment
7
Here is a summary of some of the many reasons for valuing and
maintaining biodiversity.
For human welfare
Biological diversity is important to human welfare for many reasons.
Agricultural crops derive from wild species and the high-yielding hybrids of
modern agriculture are continuously revitalised from wild genetic stock.
Future crop species that could be used directly or modified by
biotechnology are lost when entire ecosystems are wiped out. Plants are the
basis of about one fifth of prescription drugs. A number of plants
discovered in tropical rainforests or other wild areas have made significant
contributions to the treatment of serious diseases.
Loss of biodiversity disrupts ecosystems that support rainfall cycles, control
floods and affect basic global systems such as climate. In addition, loss of
species often signals the breakdown of ecosystems.
For ecological reasons
Our knowledge of the ecology of an area is rarely complete. We don’t
know what will happen if one species is removed. A good example of the
interdependence of organisms is the relationship between the cassowary and
tropical rainforests in North Queensland.
The cassowary is a large ground-dwelling bird. Cassowaries consume the
fleshy fruit of tropical rainforest trees. The seeds of the fruit pass through
the bird’s digestive system unharmed. The seed is dispersed from the parent
tree by the cassowary eating the fruit and then moving away before the
seeds are passed through the digestive system.
It is thought that the cassowary is the only organism that can eat the fruit of
these trees. The cassowary is under threat because of land clearing and the
introduction of feral species. If the cassowary becomes extinct then the
whole forest faces a problem of regeneration.
This is an example of how one key species can affect the viability of an
ecosystem. There are likely to be many similar relationships that we don’t
have information about.
For practical reasons
If we destroy an ecosystem through human impact we will be destroying
unstudied species. We should look to the precautionary principle when
deciding on the destruction of ecosystems. If we don’t know what the effect
8
Evolution of Australian biota
of an action is, we should err on the side of caution and not continue with an
action until we are more certain of the outcome.
For aesthetical and economic reasons
There is a human need to enjoy the beauty of the natural world.
People enjoy visiting areas of natural wilderness. Whether this is an innate
characteristic of humans is unknown.
It may be a biological need that drives people to visit wilderness areas.
The expanding industry of ecotourism has realised this need and provides
opportunities for people to visit natural areas. There is more money to be
made taking tourists to a tropical rainforest than there is from removing the
trees for timber.
For philosophical and ethical reasons
From an ethical standpoint, every species has as much right to exist as does
the human species. Therefore, if we can prevent the extinction of a species,
we should do so.
Preserving biodiversity
Over the last 200 years there have been dramatic changes to the Australian
environment. Rainforests have been reduced by 75% and there is an
extensive list of extinct mammals. Land has been degraded by rising salt
levels, erosion and the addition of fertilisers.
Many of the river systems have a greatly reduced rate of flow, increasing
siltation, formation of isolated waterholes, decreased flood plain soil
deposition and reduced native fish stocks.
Many species have been highlighted as worthy of being preserved.
There are campaigns to save the endangered bilby, Siberian tiger and the
giant panda. To be able to save these species it is necessary to save their
ecosystems. For within these ecosystems are the biotic and abiotic factors
required for these organisms to survive and reproduce.
An ecosystem does not have to be totally destroyed before there is an effect
on biodiversity. Even slight destabilisation of the system may lead to
extinction of some species.
Part 4: Adaptations to the Australian environment
9
A current effort to monitor biodiversity
In Australia there is a major effort to monitor the genetic biodiversity of
koalas. Koalas are the only living members of their family and they have
very low levels of genetic variation within and among populations.
By collecting data on the genetic make up of koalas, scientists are ensuring genetic
diversity in the animals that are translocated into new areas.
Since European colonisation, koala numbers have crashed and their
populations have become fragmented to the degree that their fitness is
under threat because of inbreeding. This is especially a problem in the
south-eastern parts of Australia.
Here is a clear case for conservationists to intervene to preserve the
biodiversity of these beautiful unique animals. This current effort by
wildlife managers and conservationists has identified genetic management
as an integral part of koala management.
Various populations are being monitored by a number of management units
in different environments to collect data about their genetic composition.
Once knowledge of the koalas’ genetic variations among these populations
is fully documented, future breeding programs can be planned
more carefully.
These efforts should ensure more effective and long term success of
translocating koalas to breed more vigorous and adaptable stock.
Recolonisation of populations in the most affected areas is important so that
extinction does not occur among that population. So the future of flora and
fauna management in National Parks and Wilderness regions require the
extensive monitoring of genetic biodiversity.
Do Exercise 4.2 now.
10
Evolution of Australian biota
Technological science
Many Australian species, especially the mammals, are difficult to study
because they are often small, shy, live in burrows in the ground or holes
in trees and only come out at night (nocturnal). Many naturalists, who
normally rely on direct observations to collect information on species,
have gathered extremely valuable information on the biology of
Australian animals.
The use of a range of modern techniques, including data logging, radio
tracking, radio telemetry, molecular biology (eg. genetic finger printing) and
computer modelling has often resulted in biologists being able to gain much
more detailed understanding of various aspects of the biology of species.
Although these techniques have often produced new understandings and
insights, sometimes they have simply confirmed the conclusions already
made by the careful observations of naturalists. Both approaches are
normally required and it is a usually a mistake to assume that a
technological approach will best answer a particular biological question or
test a relevant hypothesis.
Discovery of the platypus
In 1798, just over 200 years ago, John Hunter the Governor of the colony in
New South Wales observed a group of Aboriginal people spearing a
platypus in a lagoon near the Hawkesbury River not far from Sydney.
This furred species immediately caused controversy in scientific circles in
Britain, firstly as to whether it was actually a mammal and secondly as to
whether it laid eggs or gave birth to live young. The first question was
answered in 1826, when a German scientist found mammary glands in a
dead specimen which had been sent to him, but it was not until 1884 that a
young visiting biologist from Scotland finally discovered that the species
definitely did lay eggs.
Part 4: Adaptations to the Australian environment
11
Of course it should be noted that the indigenous people had known this for a
considerable time before it became known to western science!
Investigation of the biology of the platypus
For about 80 years after the discovery of its egg-laying the biology of the
species was investigated by naturalists in the field, although a great deal of
anatomical investigation was done by scientists using dissection and
microscopic techniques. However, from the 1960s onwards various
technologies were employed in the investigation of other aspects of the
biology of the platypus. These include the following technologies, which
will now be outlined.
Radio tracking
Sawpit Creek
Thredbo
River
5
15
Golden Hatchery Pools
1
Gauge pool
Intake Pool
1
Burrows
2
3 4-5 6-9 10 11-13 14
15
Platypus A
B
C
D
E
F
G
H
0
0.2 0.4 0.6
0.8 1.0 1.2
1.4 1.6 1.8 2.0 2.2
Distance along the river from Burrow 1 (km)
Distance moved by platypuses during a radio tracking study in Thredbo River.
(Reproduced from Tom Grant, The Platypus with permission of UNSW Press)
12
Evolution of Australian biota
Although direct observations had been made of the activity patterns during
daylight hours, a number of recent studies using radio transmitters have
been able to determine nocturnal activities of platypuses, as well their home
ranges and longer distance movements. The previous diagram shows the
home ranges of platypuses in a number of areas and the use of burrows in a
section of the Thredbo River in the Snowy Mountains.
Radio telemetry
It had been suggested that platypuses were unable to maintain a stable body
temperature (homeothermy) but studies using radio-transmitters, which
sense the temperature of the body, have been used to test this hypothesis.
The graph below shows the body temperature of a platypus recorded near
Jindabyne during winter conditions.
Body temperature
(∞C)
35
34
33
32
31
30
29
28
midnight
6 April
midnight
7 April
TIME
There was only slight variation around a body temperature of 32∞C in this platypus monitored by
radio transmitter (radiotelemetry), over three days during winter, in the Thredbo River. In spite of the
temperature of the water being close to freezing this animal had no trouble regulating its body
temperature. The shaded bars indicate the time when the platypus was in the water.
Body temperature of a radio-telemetered platypus in the Thredbo River.
(Reproduced from Tom Grant, The Platypus with permission of UNSW Press)
The figure following shows the activity of all five platypuses monitored
over the cold period of autumn, winter and spring, in a radiotelemetry study,
Part 4: Adaptations to the Australian environment
13
in the Thredbo River. As occurs during most of the year, majority of activity
is at night, but there is some activity in daylight hours.
Percentage of
observations
Indicating activity
60
40
20
0
0200
0600
1000
1400
1800
2200
Time of day
Activity patterns of radio-tracked platypuses in the Thredbo River.
Molecular biology techniques
The male platypus has a hollow spur, on its back legs attached to a gland
which produces venom (poison). This gland increases during the mating
season and it was thought that the spurs were used by males either to fight
for access to breeding females or in maintaining their territories.
Study of genetic relationships in a platypus population in the upper
Shoalhaven River in New South Wales, using analysis of DNA
microsatellite sequences (genetic fingerprinting), is investigating
these ideas.
Molecular biology techniques have also been used to investigate details of
the genetic make-up of the platypus. For example, it has been found that the
species has 52 chromosomes and that sex is determined by the presence of
X and Y chromosomes, as it is in humans. However, in the platypus there
are 4 Y chromosomes and 4 Xs in males and 8 X chromosomes in females,
while a human female has 2 Xs and a male an X and a Y chromosome.
14
Evolution of Australian biota
These are a few examples of how modern technology has been used to study
aspects of platypus biology which would be difficult or impossible to
determine in any other way.
However, as mentioned earlier, a good deal of what we know about much of
the biology of the species has been obtained by research not necessarily
involving such modern techniques.
Contributions of new technology
The graph makes a rough comparison between the old and the new by
estimating what percentage of current knowledge of various aspects of the
biology of the platypus that have depended on the use of modern
technology, such as radio tracking, radio telemetry, data logging and
molecular biology techniques.
These percentages have been estimated from researching a number of
scientific papers. They are very approximate but are presented in the graph
below, where 100% represents all current knowledge about particular
aspects of the biology of the platypus (and there are still many unanswered
questions) and the bars represent approximately what percentage of that
knowledge is due to the use of modern technology.
100
90
% of Knowledge
80
70
60
50
40
30
20
10
Evolution
Genetics
Reproduction
Behaviour
Activity
Thermorgulation
Feeding
0
Aspect of biology
Estimated percentage of the knowledge of aspects of the biology of the platypus
which are due to the use of modern technology.
This graph shows that, while varying amounts of information about different
aspects of the biology of this species had been gathered by biologists
without the use of modern technology, the utilisation of new techniques has
Part 4: Adaptations to the Australian environment
15
contributed greatly to the understanding of its biology, especially its
genetics, evolution and temperature regulation.
Read a scientific review article in the Additional resources. Do Exercise 4.3.
16
Evolution of Australian biota
Additional resources
Temperature regulation and hibernation
As indicated previously, part of the range of the platypus covers the
tableland and even alpine regions of eastern Australia. Its dependence on
benthic invertebrate species for its food means that in these areas
individuals must enter water at temperatures that may be as low as 0°C
during winter (Grant 1983b). In 1897, Sutherland, using an average of
three measurements made by Baron Maklouho–Maclay on one individual
platypus (Grigg et al. 1992), stated that 'the platypus, therefore, at 24.8°C
is almost a cold blooded animal'. This gave support to the idea of
phylogenetic primitiveness in the monotremes. Early in the 20th century,
however, both naturalists (Burrell 1927) and biologists (Martin 1902)
concluded that, although the platypus did have a low body temperature
when compared with other mammals (32°C), it was capable of
maintaining this temperature over a range of air temperatures. However,
the ability of the species to` maintain homeothermy in water was
doubted. No supporting evidence was given by Martin (1902), but he
commented on the ability of the platypus to regulate its body temperature
in water thus: 'Ornithorhynchus is not an amphibious animal, and only
goes into water for food or to amuse itself, and if kept too long in water
its temperature falls and it dies'. Burrell (1927), who spent inordinate
amounts of his time observing platypuses in the wild, agreed with this
conclusion. Studies of captive platypuses (Grant & Dawson 1978a,b), and
radio-telemetric work on free-ranging animals (Grant 1983b; Grigg et al.
1992), have shown the erroneous nature of these earlier conclusions, as
platypuses were found to maintain homeothermy while foraging for hours
in water below 5°C. A constant body temperature is maintained in
actively foraging animals by an increase in their metabolic activity, the
excellent fur and tissue insulation and the possession of a vascular
counter-current heat exchange system at the base of the hind legs and tail
(Grant & Dawson 1978b).
Bennett (1835, 1860) indicated that platypuses could be seen in
Australian rivers at all seasons of the year, but because of his
observations that the species was more abundant in summer than in
winter, he speculated on the possibility that individuals may ‘not in some
degree hybernate'. Burrell (1931) referred to periods of absence from the
Part 4: Adaptations to the Australian environment
17
river, such as might occur during flood flows, as 'lethargy–at times
confused with true hibernation'. Eadie (1935) and Fleay (1980) recorded
animals in captivity remaining in their nesting quarters for periods of up
to 6.5 days and inferred that they were hibernating or in a torpid state. A
number of radio-telemetered individuals, monitored during winter in the
Shoalhaven and Thredbo Rivers in New South Wales, showed no
evidence of hibernation or torpor (Grant 1983b; Grigg et al. 1992), but
similar observations to those of Fleay and Eadie were made by Serena
(1994) during winter in radio-tracked wild animals.
Unfortunately, the body temperatures of these latter animals were not
measured and the possibility of torpor or hibernation during periods of
inactivity recorded by Eadie, Fleay and Serena still needs to be resolved.
Platypuses have been known for some time to be intolerant of
temperatures higher than 25°C (Martin 1902; Robinson 1954), but
individuals in the field normally avoid such temperatures, even in the
tropical parts of their distribution, by occupying burrows where the
insulation of the soil buffers the changes in ambient temperature inside
the burrow. Grant & Dawson (19786) found that the temperature inside
an artificially constructed platypus burrow remained between 14 and 18
°C while the outside air temperature in their study area went from –5.5 to
33.5°C during the same period. Although the cooling capacity of water
means that high thermal stress does not generally occur while individuals
are foraging in water, the loss of metabolic heat produced during exercise
in water at temperatures higher than the normal body temperature of the
species means that animals cannot tolerate such water temperatures
(Grant & Dawson 1978a,b). Thermal stress during foraging in water may
be a factor involved in the limited distribution of the platypus in the
tropical north of Australia, especially on the Cape York Peninsula, where
suitable habitat seems to be available (T. R. Grant, F. N. Carrick and N I.
Griffiths, unpublished observations, cited in Griffiths (1978), and in the
rivers of the western plains areas of eastern Australia.
Source: Grant T R and Temple-Smith P D. 1998. Field biology of the platypus
(Ornithorhychus anatinus): historical and current perspectives. Philosophical
Transactions of the Royal Society of London B. 353, 1081-1091.)
18
Evolution of Australian biota
Suggested answers
1
B
The centre and central western Australia have the hottest and driest
conditions.
2
C
The monsoon conditions, with high summer but low winter rainfall
is the main reason that there are no rainforests around the Darwin
area of northern Australia.
3
B
The centre of Australia has the highest temperatures and lowest
rainfall, but it also has cold temperatures in winter, especially at
night.
4
The climate around Cairns is one of low to moderate rainfall with mild
temperatures in winter and high temperatures with rainfall in summer.
Part 4: Adaptations to the Australian environment
19
20
Evolution of Australian biota
Exercise - Part 4
Exercises 4.1 to 4.3
Name: _________________________________
Exercise 4.1: The Australian environment
Identify two areas within Australia that experience significant variation in
temperature and /or water availability.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Exercise 4.2: Biodiversity
a)
What is biodiversity?
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
b) Why is it important to maintain biodiversity?
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 4: Adaptations to the Australian environment
21
c)
Discuss (including benefits and problems) an example of a current
effort to monitor biodiversity.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Exercise 4.3: Biology of the platypus
Use the work from the course and the extract from Grant and Temple-Smith
(1998) in the Additional resources to answer the following questions.
a)
Most mammals regulate their body temperature independently of the
temperature of their environment.
i)
Does the platypus regulate its body temperature like other
mammals? Provide reasons for your answer.
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
ii) What did the early biologists think about the ability of the platypus
to regulate its body temperature?
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
iii) List the modern technological methods used to determine the
nature of temperature regulation in the platypus.
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
22
Evolution of Australian biota
b) Briefly outline two ways in which the platypus survives foraging in
water of below 5°C to obtain its food.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
c)
While observations suggest that the platypus may hibernate in cold
winter conditions, such a hypothesis does not seem to be supported by
research involving modern technological methods. Indicate whether
you agree or disagree with the hypothesis. Justify your answer.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
d) In a manual on keeping the platypus in captivity, it is stressed that the
species must be kept in an air-conditioned facility.
i)
Explain this recommendation.
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
Part 4: Adaptations to the Australian environment
23
ii) Platypuses were found to be absent from a river which seemed to
have enough food for them and banks for them to dig their
burrows, but which had an average summer water temperature of
33°C. Explain briefly why you think platypuses may not have been
found in this river
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
e)
Early naturalists thought that platypuses were only active at dawn and
dusk and yet modern studies tell us a different story. Describe the daily
activity pattern of the platypus and briefly explain why the naturalists
could have come up with a different conclusion.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
24
Evolution of Australian biota
Gill Sans Bold
Biology
Preliminary Course
Stage 6
Evolution of Australian biota
Part 5: Reproductive adaptations
0
0
2
I
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b
to T S
c
O EN
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in D M
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a
r EN
o
p
or AM
c
n
2
Contents
Introduction ............................................................................... 2
Cell division ............................................................................... 4
Mitosis...................................................................................................4
Meiosis................................................................................................10
Comparing the processes..................................................................17
So why sexual reproduction? .................................................. 18
External versus internal fertilisation...................................................18
Case studies of reproductive adaptations ............................... 25
The water holding frog .......................................................................25
Red kangaroo (Macropus rufus)........................................................26
Mistletoe plants and mistletoe bird ....................................................26
Eungella gastric-brooding frog...........................................................27
Pollination in native plants .................................................................29
Suggested answers................................................................. 33
Exercises – Part 5 ................................................................... 35
Part 5: Reproductive adaptations
1
Introduction
As has been discussed throughout this module so far, natural selection by
the environment has led to the evolution of new species during the long
periods of time which have elapsed since the appearance of the first life
on Earth. Only those organisms which are adapted to their surrounding
environments are successful. However, success does not just rely on
survival, it also depends on reproduction.
This process of reproduction passes on the genes controlling the
adaptations for survival from one generation to the next. (Details of the
way in which characteristics are determined and how these are inherited
will be discussed in the HSC modules.) In order to continue to live in its
environment an organism must survive and reproduce.
In this part a number of aspects of reproduction will be considered,
including discussion of some of the unique adaptations for reproduction
found in species of Australian biota.
In Part 5 you will have opportunities to learn to:
•
distinguish between the processes of meiosis and mitosis in terms of
daughter cells produced
•
compare and contrast external and internal fertilisation
•
discuss the relative success of these forms of fertilisation in relation
to colonisation of terrestrial and aquatic environments
•
describe some mechanisms found in Australian flora for:
–
pollination
–
seed dispersal
–
asexual reproduction
with reference to local examples
•
2
describe some mechanisms found in Australian fauna to ensure:
–
fertilisation
–
survival of the embryo and of the young after birth
Evolution of Australia biota
•
explain how the evolution of these reproductive adaptations has
increased the chances of continuity of the species in the Australian
environment
•
describe the conditions under which asexual reproduction is
advantageous, with reference to specific Australian examples.
In this part you will be given opportunities to:
•
analyse information from secondary sources to tabulate the
differences that distinguish the processes of mitosis and meiosis
•
identify data sources, gather, process and analyse information from
secondary sources and use available evidence to discuss the relative
success of internal and external fertilisation in relation to
colonisation of terrestrial and aquatic environments
•
plan, choose equipment or resources and perform a first-hand
investigation to gather and present information about flowers of
native species of angiosperms to identify features that may be
adaptations to wind and insect/bird/mammal pollination
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. Revised November 2002. The most up-to-date version can be
found on the Board's website at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html
Part 5: Reproductive adaptations
3
Cell division
Consider that you started life as a single cell, a fertilised egg or zygote,
just barely visible by the unaided eye. From those humble beginnings
you ended up consisting of 1014 (100 billion) cells. You initially
weighed 1.5 millionths of a gram and now weigh tens of kilograms.
Two processes involved in your growth from a zygote have been:
∑
cell division – the production of new cells by mitosis
∑
cell differentiation (or specialisation) – changes in cells associated
with their specialised functions. For example, heart muscle cells are
different from the cells making up the muscles which produce
movement of the skeleton, lung cells are different from kidney or
liver cells.
These two processes are also involved in repair of damaged tissues, such
as a cut finger or a broken bone. In some organisms, especially plants
and some simple animals, these two processes can result in the
production of new individuals by asexual reproduction. This occurs
when a new individual is produced without the fertilisation of gametes or
sex cells, as occurred in the production of the zygote from which you
developed (from sexual reproduction.)
The type of cell division leading to the production of gametes is
called meiosis.
Mitosis
In Patterns in nature you looked at the progress of chromosomes through
the process of mitotic division. You will probably remember that this
process involves the duplication of chromosomes in the nucleus of a cell,
followed by division of the nucleus (mitosis) and finally division of the
cell itself (cytokinesis).
4
Evolution of Australia biota
Because the chromosomes are duplicated, there are two copies of each
chromosome in the cell before it divides, but after it divides there are
two cells, each with the same chromosome make-up as the original cell.
The daughter cells, as they are called, are genetically identical to
each other.
46
(23 pairs)
diploid
duplication
92
nuclear division
and
cytokinesis
46
(23 pairs)
diploid
46
(23 pairs)
diploid
cell growth
cell growth
46
(23 pairs)
diploid
46
(23 pairs)
diploid
The process of mitosis produces two identical daughter cells.
The flow chart shows the process of cell division where humans are used
as an example. Remember that different species have different numbers
of chromosomes. For example, humans have 23 pairs or a total of
46 chromosomes, while the platypus has 26 pairs, a total of
52 chromosomes.
Part 5: Reproductive adaptations
5
Asexual reproduction
Complete new organisms can be produced by new cells being formed by
mitosis, followed by cell differentiation.
Many plants can reproduce asexually. Some of these methods are
outlined following.
Cuttings or pieces
You might have grown plants in your garden or in a pot by taking a
cutting from another plant and just pushing into the soil. It grew new
roots and leaves. Various species of willows introduced into Australia
have been grown in this way. Even bits of willow which get broken off
by wind can result in new willow trees.
plastic bag
sticks
fresh cutting
elastic band
tissue forms
on base
new roots form
Cuttings are usually shoots cut from a desired plant. When planted in moist
soil, they grow roots and form a new plant. Geraniums and carnations are often
spread by cuttings.
Caulerpa taxifolia is a noxious algae growing in NSW estuaries.
It is successful at moving into new areas because a complete plant can
grow from a piece of plant material that is less than 1 mm in size.
6
Evolution of Australia biota
Runners
Some lawn plants send out a runner for which roots grow to produce a
new grass plant. They stay joined together, but if you cut the runner with
a mower they become two separate grass plants. Dusky coral peas
produce new individuals in the same way.
RUNNERS are long, thin stems which grow along the ground from the parent
plant. Roots and buds appear at the end of the runners and new plants develop
from these. Eventually, the runner rots, leaving each new plant on its own.
Since each parent plant produces a number of runners, a very dense patch of
plants can form, crowding out the competition
Tubers
A number of Australian trees and shrubs (eg. snowgums , Angophoras
and some Banksia species) are burnt by fire and appear dead, but will
resprout from a thickened part of the stem just below the surface of the
soil where they are protected from the heat of the fire. This thickened
part of the stem is called a lignotuber.
Part 5: Reproductive adaptations
7
After a fire this Angophora is sprouting from the lignotuber at ground level.
(Photo: Jane West)
A new potato plant grows from underground stems and roots which form
from the buds (‘eyes’) of a potato. The original potato tuber provides
food as stored starch. This provides the energy necessary for the growth
of the new potato plant.
Once the new plant starts to carry out photosynthesis it begins to form
tubers under the ground and to store starch in these. Eventually the plant
dies and you (or the farmer) digs up the new potato tubers. If you missed
digging one up it will sprout into a new potato plant the following year.
Plants which die at the end of each growing season but regrow new
individuals either through asexual reproduction or by seed are called
annual plants.
8
Evolution of Australia biota
new shoot
swollen stem bud
(tuber)
tuber
Spores
Ferns reproduce from spores which are shed from the brown sporeforming bodies which you might have seen under fern fronds. A spore
consists of a single cell or a group of a few cells which can grow into a
new individual. Mosses and fungi also reproduce asexually by means
of spores.
Fern spores. (Photo; Jane West)
Spore capsules on a moss.
(Photo: Jane West)
Bulbs
Daffodils and tulips develop bulbs before the plant dies at the end of the
summer and then grow again from these dormant bulbs the next spring.
In all of these instances of asexual reproduction the new plants are
genetically identical to the original plant from which they came – their
Part 5: Reproductive adaptations
9
chromosomes are exactly the same. The reason is that the cells of the
new plant divided by mitosis from those of the original plant.
bud
stem (long section)
Cross-section of an onion bulb.
Colonisation
Asexual reproduction results in the production of large numbers of
offspring which are normally well adapted to the current environment
and so permit species to occupy an area and often to colonise other areas.
Desert grasses, such as the porcupine grass (Triodia scariosa), and
grasses growing on sand dunes (Spinifex sericeus) reproduce quickly by
runners to occupy suitable areas. Many species which can regenerate
after fire from remnant lignotubers, also are carrying out asexual
reproduction. New individuals are being produced from the remains of
the burnt plants.
Native ferns also reproduce from spores, as do the fungi (including
mushrooms and puff balls) found on the floors of Australian forests.
If this form of reproduction is so successful, you might ask why do most
species also carry out sexual reproduction? A very good question indeed.
Meiosis
Sexual reproduction occurs when the genetic material from the
nucleus of a female sex cell joins with the nucleus of a male sex cell.
This process is called fertilisation, as you will probably remember and
the sex cells are gametes.
The process of fertilisation is preceded by meiosis, or meiotic cell
division, which results in each gamete having half the number of
chromosomes of the original parent cells. During meiosis the
chromosomes duplicate, just as they do in mitosis, but the cell divides
10
Evolution of Australia biota
twice, resulting in a halving of the chromosome number. The sperm or
egg in a platypus, for instance, has 26 chromosomes, while the adult has
52 chromosomes in each of its body cells. The flow chart below shows
some of the changes in chromosome number during the process of
meiosis. The diagram below shows meiosis in humans.
46
(23 pairs)
diploid
duplication
92
nuclear division
and
cytokinesis I
46
46
nuclear division
and
cytokinesis II
nuclear division
and
cytokinesis II
23
haploid
23
haploid
23
haploid
23
haploid
Meiosis produces gametes with half the number of chromosomes of other
body cells.
Chromosomes occur in pairs. For example, you inherited one of each of
your 23 pairs of chromosomes from your mother’s egg and the other 23
from your father’s sperm. You received 46 individual chromosomes but
these consisted of 23 pairs. If you are male then the 23rd pair consisted
of one X chromosome from the egg and one Y from the sperm. If you
are female then you inherited an X from both the sperm and the egg.
During the process of meiosis the chromosomes are assorted in different
combinations and some bits of chromosomes even get exchanged
between members of a pair.
Part 5: Reproductive adaptations
11
This process is called crossing-over. This process and the mechanism of
assortment will be dealt with in later HSC work. However, it should be
noted here that these two processes result in meiosis not only halving the
number of chromosomes, but also producing genetic variation within
the gametes.
If you were to look at a group of green and golden bell frogs, a flock of
seagulls or several platypuses, you could probably not pick the
differences between each individual in the group (although they probably
could pick the differences between each other).
If you look around a crowd people you will notice that all human
beings are different from each other. Although you have the same
parents, unless you are an identical twin, even your brothers and sisters
look different from you and from your parents. Meiosis leads to
genetic variability.
Sexual reproduction
It is really important to bring about the halving of the number of
chromosomes in the gametes, otherwise every time two gametes
fertilised each other, the number of chromosomes would double.
Have a look at the next diagram, where the top half shows what would
happen in an imaginary life cycle of the green and golden bell frog with
gametes being produced by mitosis. (This does not normally happen, of
course, in nature!)
The lower diagram is the real life cycle as occurs when gametes are
produced by meiosis. Unless meiosis takes place, the number of
chromosomes in the young adult will keep doubling. Normally adult
cells have the double, or paired number of chromosomes (diploid)
number and the gametes the single or unpaired (haploid) number
of chromosomes.
12
Evolution of Australia biota
adult female green and
golden bell frog
26 chromosomes
egg
26
mitosis
fertilisation
adult male green and
golden bell Frog
26 chromosomes
mitosis
zygote
52
sperm
26
OOPS!
too many chromosomes
young adult
52
larval stagetadpole
52
embryo
52
What would happen if frog gametes were produced by mitosis.
adult female green and
Golden Bell frog
26 chromosomes
egg
13
meiosis
fertilisation
adult male green and
golden bell frog
26 chromosomes
young adult
male or female
26
meiosis
zygote
26
sperm
13
larval stagetadpole
26
embryo
26
The lifecycle of the green and golden bell frog.
Part 5: Reproductive adaptations
13
In the life cycle of the green and golden bell frog (Litoria aurea), there is
a larval stage, the tadpole. In most cases where larval stages occur they
are involved in either or both of the following processes outlined below.
•
Feeding and growth – Quite a number of insects which live near
water have aquatic larval stages (eg. mosquitoes, mayflies and
dragonflies). Caterpillars are the larval stages of moths and
butterflies. These stages feed ravenously to produce the energy
and materials necessary to allow the animals to develop into the
adult stage.
•
Dispersal – Most invertebrate animal species found in water,
including rock oysters and the corals which make up the
Great Barrier Reef, produce larval stages which either swim or are
carried along by the water flow or water currents. Species colonise
other areas in this way.
In flowering plants the male gametes are the pollen grains produced by
the anthers of the flower and the female gamete is a cell found in the
ovule inside the ovary of the female part of the flower. Both of these are
produced by the process of meiosis and so have half the adult number of
chromosomes in their nuclei.
The general structure of a flower is shown below.
filament
style
pistil
stigma
stamen
anther
ovary
ovule
petal
sepal
Cross section of a simple flower to show the various parts referred to in the
discussion of reproduction in flowering plants.
14
Evolution of Australia biota
In most flowering plants there are both male and female parts, although
in some, such as passionfruit, kiwifruit and Casuarina (sheoaks) there are
separate male and female plants.
When a pollen grain settles on the stigma of a receptive plant, a tube
grows down into the ovary and the nucleus from the pollen moves down
this tube to fertilise the female gamete nucleus inside the ovule.
The fertilised egg cell develops into an embryo found inside the ovule,
which becomes the seed. The ovary becomes the fruit after flowering
has taken place.
Pollination and fertilisation in a typical flowering plant.
Pollination
In a flowering plant fertilisation actually occurs in the ovary, but the
pollen has to be transferred to the female part of the plant by wind or a
variety of living agents like insects, small mammals and birds.
The process of the pollen reaching the sticky surface of the stigma of the
female part of a plant is called pollination.
Living pollinating agents are attracted to the flower by its smell, colour,
shape and availability of a food source, especially nectar, but also the
pollen itself. As an insect, small mammal or bird brushes past the anther
it picks up pollen and deposits it when it touches a stigma.
In most species the pollen is produced at a different time than when the
stigma can receive it, so that plants are not usually pollinated by their
own pollen (self pollination). In most instances flowers are pollinated
with pollen from other plants of the same species (cross pollination).
This insures greater variation in the offspring.
Part 5: Reproductive adaptations
15
Bees are perhaps the most recognised pollinating agent, carrying pollen
from one flower to another as they seek out nectar, from which they
produce honey.
Pollinators of Australian plants include ants, bees and birds.
However, many Australian flowers are also pollinated by birds,
especially the honeyeaters (eg. wattle birds, noisy miners, spinebills), and
by small mammals like the pygmy possums, some of the marsupial mice
(more correctly called marsupial carnivores or insectivores, like the
various species of Antechinus).
A rainbow lorikeet feeding on a Grevillea sp (Photo: D. Gonzalvez).
16
Evolution of Australia biota
There is even a tiny marsupial called the honey possum which pollinates
flowers in Western Australia where it is found. Common species found
in the bush and in gardens throughout Australia are pollinated by these
vertebrate species, including many of the bottlebrush (Callistemon),
Banksia and Grevillea species. Many of these pollinating species have
brush-tipped tongues for penetrating the flowers to gather nectar.
Pygmy possums weighing only around 24 grams, feed mainly on nectar
and pollen, but will also take insects in their diet.
Wind is responsible for pollinating many Australian plant species,
especially the grasses. In these species the anthers are very long and
produce large amounts of light pollen, which is easily picked up by the
wind passing over the flowers. Usually the stigmas are also very large
and spread out to receive pollen carried by the wind.
Comparing the processes
As you will realise from the amount of time already spent on the discussion
of cell division and reproduction, the processes of mitosis and meiosis are
extremely important in biology. So it is essential that you have a good
understanding of them. Read through the material covered so far in Part 5 of
this module and then fill in the table for Exercise 5.1.
Part 5: Reproductive adaptations
17
So, why sexual reproduction?
What has been discussed so far does not really answer the question,
which was raised earlier. Mitosis and asexual reproduction results in
large numbers of offspring, which are identical and well adapted to
survive and reproduce. But, meiosis results in lots of different offspring.
Sexual reproduction further increases the difference between offspring
depending on who the parents were and not just due to the fact that the
gametes are different from each other.
Organisms carry out sexual reproduction because the presence of such
variation means that there may be individuals in the population which are
adapted to any environmental changes which might occur. You will
probably remember that this idea was discussed earlier, in Part 1 of
this module.
Sexual reproduction provides the variation which is acted on by the
process of natural selection to produce changes in a population when the
environment changes. Remember that it is these changes over time and
with changing environmental factors which almost certainly explains the
evolution of new species.
There is no variation from asexual reproduction, but self-fertilisation also
produces less variation due to the fact that the parents of both gametes
are the same. For that reason, cross fertilisation normally occurs in
sexual reproduction.
External versus internal fertilisation
It is almost certain that life evolved in the sea and then later proceeded
onto land. Undoubtedly, most of the early animals and plants living in
water were fertilised outside the body (external fertilisation).
Gametes were released into the water in large numbers and at least some
male and female gametes came together – fertilisation.
18
Evolution of Australia biota
External fertilisation is still found in most invertebrate and plant species
living in water today. The corals of the Great Barrier Reef for example
all release their gametes into the sea, often at the same time, causing the
water to become, cloudy with the vast numbers of swimming sperm and
eggs released. Larval stages are usually found in species which carry out
external fertilisation, including vertebrates like fish and amphibians.
Once organisms moved onto land external fertilisation became more
difficult as gametes normally need to be kept from drying out and to be
in a fluid which brings them together. However external fertilisation has
persisted but only in plants and animals which live under moist
conditions, such as mosses and ferns, a few amphibians and some
invertebrate species.
Fertilisation in insects of reptiles, birds and mammals occurs inside their
bodies (internal fertilisation). Fluid provides a medium in which the
male gametes move. Internal fertilisation avoids the problems of gamete
transfer and the dry conditions found on land.
Three other strategies have evolved in terrestrial species which have also
permitted the permanent colonisation of land, including very arid
environments which have come to occupy a great deal of the Australian
mainland. The advantages of seeds, eggs and internal fertilisation will
now be examined.
Seeds
Plants produce seeds which can withstand dry conditions. When water is
available, embryos within the seeds germinate to produce seedlings and
then adult plants. Food material is stored within special areas within
the seed.
A lot of Australian plant species grow quickly from seeds after the adult
plants have been destroyed by fire. In some species, including most of
the Banksias, the seeds are not released from the dried out fruit until it
has been burnt by fire. This means that the young seedlings are not
competing with adult plants for nutrients from the soil.
There are a host of different mechanisms which permit seeds to be
dispersed in the environment to insure the replacement of older plants, to
recolonise areas which have been burnt or been exposed to drought and
to colonise new areas. The diagram below shows a number of ways
seeds can be dispersed.
Part 5: Reproductive adaptations
19
Dispersal mechanisms
Examples
Water dispersal
Coconuts grow in areas near oceans.
The coconuts fall into the water and
can float for thousands of kilometres.
Animal dispersal
Many seeds have hooks and burrs as
part of their seeds. These become
trapped in the fur or feathers and are
transported by animals far from the
parent plants.
burrs
Wind dispersal
Many seeds have light feathery fruit
that are easily blown by the wind.
Self-dispersal
Some seeds have explosive
mechanisms that fling the seeds away
from the parent plant.
20
Evolution of Australia biota
Many seeds are dispersed by humans. Can you suggest some ways in
which you may have dispersed seeds from one place to another.
Many plant weed species have been spread inadvertently by humans.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answer.
Eggs
The eggs of the insects, birds and the monotreme mammals are relatively
impervious to water so that the developing embryo inside the egg is
protected from drying out in terrestrial environments. Within the egg a
yolk provides a source of energy for the embryo to grow until the young
hatches from the egg.
Internal development
In all mammals, except the monotremes (platypus and echidnas)
development of the embryo occurs inside the uterus (womb) of
the female.
In marsupials the developing embryo is born at a very poorly developed
stage and completes its development in the pouch where it receives milk
produced by the mammary glands.
Part 5: Reproductive adaptations
21
Young red kangaroo. (Photo: © Griffiths, M. 1978. The Biology of the
monotremes. Academic Press.)
In placental mammals, including humans, a well developed placenta
forms from tissues of the embryo and the wall of the mother’s uterus.
Diffusion between the blood vessels in the placenta and the uterus allows
oxygen and food molecules to be taken up by the developing embryo
from the mother’s blood and waste products to be passed back into the
blood of the mother.
The young of placental mammals vary in the stage of development they
reach before they are born. For example, the young of rats and mice are
bald, blind and helpless when they are born, while the young of an
African antelope or zebra can run with the herd within a few hours of
being born.
However, all placental mammals are born in a much more advanced
stage of development than any of the marsupial species. The young of
the red kangaroo for example only weighs a few grams when it is born,
while the adult kangaroo is around the size of a human. The photograph
above shows a newborn red kangaroo attached to the teat in its mother’s
pouch. At this stage it is not much bigger than the size of a jelly bean!
Although the platypus and echidnas lay eggs the young are hatched at
about the same stage as marsupial young. They then complete their
development on milk from the mammary glands.
22
Evolution of Australia biota
A young echidna. (Photo: © Griffiths, M. 1978. The Biology of the
Monotremes. Academic Press.)
In the echidna this development takes place inside a temporary pouch on
the abdomen of the mother and then in a burrow. In the platypus the
whole development takes place in a burrow constructed by the mother in
the bank of the river.
A young echidna hatching from the egg appears in the previous
photograph. The size can be judged from the fingers of the hand in
which the young is held.
While internal development is the rule for non-monotreme mammals,
it also occurs in some fishes (eg. some sharks), a few amphibians
(eg. gastric-brooding frog) and some reptiles (eg. a number of skink
lizard species and some snakes) in Australia.
In these situations the eggs do not form a waterproof shell and young
hatch inside the adult but are nourished mainly by the food stored in the
yolk of the eggs, although in some cases a rudimentary placenta is
formed which permits exchange of materials between the developing
young and the mother.
All of these strategies have evolved to ensure survival of the embryo
until it is born (or hatched). In marsupials survival after birth is brought
about by the attachment of the young to the teats from the mammary
glands. In most Australian marsupials the developing young are housed
within a pouch. But in some, marsupials particularly the small
Part 5: Reproductive adaptations
23
carnivorous species, the pouch is very poorly developed and the young
are literally carried around hanging from the mother’s teats!
Large numbers of gametes are normally produced as many do not survive
in species which carry out external fertilisation. Large numbers insure
that at least some will fertilise each other and so lead to the production
of offspring.
Even when offspring are produced, many of them do not survive.
However, some species have few young but look after them well so that
most survive. In general, animals which have external fertilisation have
large numbers of potential offspring but have a high death rate of the
young, while those with internal fertilisation, especially those with
internal development, have fewer young with a lower mortality.
Do Exercise 5.2 now.
24
Evolution of Australia biota
Case studies of reproductive
adaptations
Many of our local plants and animals have adaptations that increase the
chance of survival of the young. There are some examples below.
The water holding frog
The water holding frog (Cyclorana platycephala) is one of several
Australian species of burrowing frogs which live in arid conditions,
a rather unusual place for frogs to live you would expect! Frogs have
external fertilisation and so must have water in which to mate and
produce tadpoles.
Rainfall over many of Australia’s arid areas is less than 20 cm per year
on average, but the rainfall is normally irregular and may come in large
downpours, which create many pools in which frogs can live and breed.
There are a number of species of invertebrates which hatch from dormant
eggs when rain occurs and these provide food for frogs.
The frogs themselves have survived the extended dry periods by living in
a cocoon about 0.5 m underground. When the temporary pools in which
they lived began to dry up the frogs buried down into the soil, away from
the heat of the sun, and formed cocoons around themselves made from
dead skin and mucus secreted by the skin. This cocoon is quite
impermeable to water and so their water losses to the surroundings has
been low.
These frogs can tolerate some dehydration (loss of body fluids) and an
increase in toxic waste products arising from their metabolism, which has
been lowered during their time underground. As soon as the water from
the new rains soaked down to them, the frogs break out of their cocoons
and make their way back to the surface to feed and mate in the pools.
As the time that these temporary pools last in a dry environment is often
quite short, the frogs have a reproductive adaptation for survival.
The time taken for tadpoles of related species to develop into frogs is
Part 5: Reproductive adaptations
25
several months, but in this desert species, the tadpole becomes a fully
developed frog within only 30 days. Hopefully this occurs before the
pool has dried out and in time for these frogs to burrow underground and
wait until the next rains, which may even be a year or more away.
Red kangaroo (Macropus rufus)
The red kangaroo has the ability to survive in a hot, dry environment.
The species is also adapted for reproduction in a habitat where food
supply can be very poor due to drought conditions.
During good conditions female red kangaroos have one young-at-foot
(which is not yet independent and still feeding from milk from a teat in
the pouch), one young suckling in the pouch and a dormant embryo in
the uterus. Once the young leaves the pouch and the young-at-foot
becomes independent, the dormant embryo starts to develop, is born
and enters the pouch. Immediately after this birth, the female mates
again and another dormant embryo develops. This is called
embryonic diapause.
As a result of this reproductive strategy, the red kangaroo can continue to
reproduce under drought conditions. Once food becomes short the
young-at-foot is no longer fed. If it is old enough it will survive on its
own but if not it will die. The young in the pouch survives for some time
and will become a new recruit to the population if conditions get better,
but will die if the mother becomes too poorly nourished to produce
enough milk.
However, once this happens the dormant embryo develops, is born and
moves into the pouch. Again, if conditions improve this young will
survive but will die if the drought is long and very severe. At this point
females no longer breed but immediately begin to breed again within a
week or so after food again becomes available. A tough life for the
young that die, but the evolution of this reproductive strategy ensures the
survival of the species.
Mistletoe plants and mistletoe bird
Mistletoe plants belong to a family of flowering plants whose seeds
germinate on other plant species, the host. The developing seedlings
grow special root-like structures into the branches, or occasionally roots,
of other plant species. This structure penetrates the xylem of the other
plant and the mistletoe obtains its supply of water and minerals from the
other plant. Mistletoes are therefore parasites.
26
Evolution of Australia biota
There are 84 species of mistletoe in Australia and most have their seeds
dispersed by one species of bird, the mistletoe bird. The mistletoe fruits
are sweet, sticky and attractive to mistletoe birds.
The digestive system of the mistletoe bird is very short and the seeds
pass through in less than 25 minutes. The mistletoe bird defaecates and
wipes its sticky faeces (droppings) onto branches on which it is perched.
The Mistletoe seed survives passing through the mistletoe bird,
germinates and starts to grow on the branch.
Because the range of mistletoe species produce fruits at different times of
the year, the mistletoe bird has a constant supply of food and is available
as a disperser of seeds because of its nomadic nature and its strange
toilet habits!
The Eungella gastric-brooding frog
The Eungella gastric–brooding frog (Rheobatrachus vitellinus) occurs in
a small area of northern Queensland. It mates in the water and after
external fertilisation the female eats the small number of eggs produced,
(around 25) which then develop in her stomach, first into tadpoles and
then into small frogs.
The normal digestive mechanisms and the urge to eat in the mother are
suppressed during this peculiar pregnancy. The mother actually lives in a
burrow during the pregnancy but occasionally goes to the water, where
she lets the tadpoles, and later the little frogs, out into the water to feed.
If a predator is about she quickly eats them again and returns to the
burrow. The young remain in the stomach for at least six weeks.
Remember that most adaptations are a result of natural selection acting
to eliminate a characteristic which is not beneficial to survival and
reproduction or favouring one which is beneficial. What do you think
the benefit of this reproductive strategy might be for the gastric
brooding frog?
_________________________________________________________
Check your answer.
Banksia serrata
As well as specialised pollination mechanisms Banksias have other
reproductive adaptations to increase survival. Plants such as Banksia
serrata only open their seedpods when they have been burnt.
Part 5: Reproductive adaptations
27
Banksia before a fire. (Photo: J West)
Banksia after a fire. (Photo: J West)
This means that the seeds do not have to compete with the parent plants
and can grow in a soil that has been enriched from the ash of the fires.
They also have regrowth from lignotubers and epicormic shoots.
Regrowth after a fire from epicormic shoots in Angophora sp. (Photo: J West).
The tough thick bark of this Banksia protects it during the fires however
Banksia ericifolia does not have this thick bark and is killed by fire.
28
Evolution of Australia biota
Pollination mechanisms in
native plants
As mentioned, many Australian plants are pollinated by animals, while
others are pollinated by wind.
Banksia
Banksias are a member of the Proteaceae family which is a Gondwanan
group of plants. Their distinctive flowers (spikes) consist of thousands of
individual flowers grouped together in an inflorescence. The grouping of
flowers gives a rich reward to any pollinator that visits and provides a
large flower that is easy to find. The flowers are often seen dripping with
nectar and this acts an attractant to insects and birds.
The flower first appears as a solid cylinder and starts to open usually
from the top. In Banksia ericifolia there are four anthers and a hooked
style. At first the style is hooked underneath the stamens. The male
parts of the flowers mature at first and are then released. This prevents
self-fertilisation from occurring.
Banksia ericifolia - notice the bee visiting the flowers (Photo: Jane West).
Part 5: Reproductive adaptations
29
Grevillea
Grevilleas are another member of the Proteaceae family. The flower
consists of an inflorescence with many individual flowers grouped
together as an attractant to pollinators.
Grevillea inflorescence (Photo: Jane West).
The structure of the individual Grevillea flower (Photo: Jane West).
Around the place where you live there will be a range of flowering plant
species which is an outdoor laboratory for you to study, even if it is just the
pot plants on the balcony or veranda.
If you are unable to find some flowers the pictures from this part of the
module can be viewed in colour on the Science online website:
www.lmpc.edu.au/science
30
Evolution of Australia biota
There are some safety issues here to consider. You will have to cut open a
flower. Be careful whenever you use cutting implements.
Here is what you have to do.
Procedure:
Select two species of flowering plant with very different flower shapes.
You may pick a bell-shaped flower like a lily or hibiscus and possibly
a complex flower head (inflorescence) such as a bottlebrush or
Banksia species.
1
Select two flower species. Try to pick native species if they are
flowering.
2
Use books, ask your local flower shop or nursery or use other
sources to find out the name of the plant species you have chosen.
3
Take one flower from the plant and dissect it with a hard-backed
razor blade or sharp knife - it may also be useful to use forceps
(tweezers) to hold the parts as you separate them. Try to identify the
following structures which were shown in the diagram in the notes.
•
anther (usually yellow in colour due to the pollen)
•
filament (this supports the anther). These make up the stamen
there are usually many stamens in each flower.
•
stigma (often sticky to receive the pollen) these also protrude
from the flower but there is usually only one per flower
•
style (this connects the stigma to the ovary)
•
ovary
•
petals (if they are present - bottle brushes and gums don’t have
any).
Remember that some flowers, like the bottlebrushes, Banksias and
Grevilleas consist of many flowers.
5
Draw a picture of an individual flower and/or take a photograph of
it. Label the parts of the flowers that you can identify.
Part 5: Reproductive adaptations
31
Lambertia formosa - bird pollinated plant. (Photo: Jane West)
6
Observe the flowers to find out how they are pollinated - watch for
birds or insects visiting them or for pollen being blown in the wind
7
Discuss ways in which the flowers may be adapted to attract
pollinating animals or how they are modified to take advantage of
the wind as a pollinating agent.
Try to find out by observation or by consulting sources how the
animal pollinators may be adapted to obtain what they need from the
flower and how they produce pollination.
8
For example: you might observe a red wattle bird probing its curved
beak between the flowers in the flower head of a bottle brush and
its long brush-tipped tongue extracting nectar, or a honey bee
(an introduced species) disappearing into the bell of a lily flower and
coming out covered in pollen.
Record your observations, discussion and drawings in a short report in
Exercise 5.3.
32
Evolution of Australia biota
Suggested answers
Seeds
Did you think about any of the following?
•
Seeds on a travelling rug which you sat on while having a picnic in
one place and then used in another area.
•
Seeds in your socks, which you were wearing when walking through
a paddock in the country and picked out when you got home, or even
when you went to another country area.
•
Seeds stuck to your dog’s ears after a run through a park which you
picked off on the way home.
The Eungella gastric – brooding frog
The description indicates that the species produces a ‘small number of
eggs’. You will remember that species which have external fertilisation
normally produce very large numbers of eggs indeed, as many drift
away, die or get eaten by predators. The gastric brooding frog has a very
high rate of success in rearing its young as they are well looked after by
the mother. Unfortunately, this strategy has not continued to be as
successful since human activities have changed many Australian
ecosystems. A related species of the gastric brooding frog is now extinct.
The Eungella species has not been seen for some time and may also be
close to extinction.
Part 5: Reproductive adaptations
33
34
Evolution of Australia biota
Exercises - Part 5
Exercises 5.1 to 5.3
Name: _________________________________
Exercise 5.1: Mitosis and meiosis
Fill in the table to show the differences between the processes of mitosis
and meiosis.
Questions
Mitosis
1
Does duplication of chromosomes occur in the
process?
yes
2
How many cell divisions occur during the
process?
3
Compared to the number of chromosomes
found in cells before the process, how many are
found in the daughter cells? (eg. if an organism
had 42 chromosomes in its adult cells, how
many would be in the daughter cells after the
process?)
4
How similar is the genetic make-up of the
daughter cells to each other and to the original
parent cell?
identical
5
What activities carried out by living organisms
involve the process?
growth
Meiosis
two
Exercise 5.2: Sexual reproduction
a)
Describe and give an example of external fertilisation.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 5: Reproductive adaptations
35
b) Describe and give an example of internal fertilisation.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
c)
Compare and contrast external and internal fertilization
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
d) External fertilisation is more common in aquatic organisms than in
terrestrial organisms. Discuss reasons for this.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Exercise 5.3: Flowering plants
Record your observations of the flowers of two plants, include discussion
and drawings (or photographs) in a short report of about two pages.
Use your own paper and attach to this sheet.
36
Evolution of Australia biota
Gill Sans Bold
Biology
Preliminary Course
Stage 6
Evolution of Australian biota
Part 6: Evolution, survival and extinction
0
0
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Contents
Introduction ............................................................................... 2
Mass extinctions........................................................................ 4
Specialisation and extinction ...............................................................5
Extinction due to human activity ..........................................................6
Evolutionary survival and extinction .......................................... 9
Summary................................................................................. 11
Suggested answers................................................................. 17
Exercises – Part 6 ................................................................... 21
Part 6: Evolution, survival and extinction
1
Introduction
As was discussed earlier in this module, extinction is often part of the
evolutionary process. If conditions in an environment change and no
individuals in a population of a species have a genetic make-up which
permits them to survive and reproduce under the new environmental
conditions, that population of the species will become extinct.
When global environmental changes occurred over time many species on
Earth became extinct. Of all the millions of species, which have evolved
over the 4.7 billion years since life began on Earth, more than 99% of
them are now extinct.
On average, most species of organisms survive for between one and ten
million years, although a few species have survived much longer than
that. Modern humans have been on the Earth for only about 100 000
years so far, but in that time have had considerable effect on the
ecosystems of the planet, including being directly responsible for
processes which have resulted in the early extinction of other species.
The study of the evolution of species through time and an understanding
of the possible changes to past environments may permit some prediction
of the nature of future ecosystems. Although the processes are complex
and the gaps in knowledge must make any predictions quite tentative,
this module discusses such predictions and the evidence which permits
them to be suggested.
In this part you will be given opportunities to learn to:
2
•
explain the importance of the study of past environments in
predicting the impact of human activity in present environments
•
identify the ways in which palaeontology assists understanding of
the factors that may determine distribution of flora and fauna in
present and future environments.
Evolution of Australian biota
In this part you will be given opportunities to:
•
gather, process and analyse information from secondary sources and
use available evidence to propose reasons for the evolution, survival
and extinction of species, with reference to specific Australian
examples.
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. Revised November 2002. The most up-to-date version can be
found on the Board's website at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html
Part 6: Evolution, survival and extinction
3
Mass extinctions
Throughout geological time, since the appearance of living organisms on
Earth, there have been five mass extinction events. These are events
where more than 75% of species in existence at the time became extinct.
These are shown in the table below.
Period
Time
Nature of event
end Ordovician
441 mya
85% of all species wiped out
late Devonian
365 mya
two waves of extinction, especially marine
species
end Permian
251.4 mya
96% extinction, including mammal-like reptiles
end Triassic
200 mya
75% of species, especially marine forms extinct
Cretaceous
65 mya
75-80% become extinct, including the dinosaurs
Except for the mass extinction 65 mya at the end of the Cretaceous
Period, all of the other four extinction events appear to have been due to
changes in climate, sea levels, ocean current circulation, volcanic activity
and tectonic plate movements. As was discussed in Part 2 of this
module, all of these things interact with each other to produce change in
climate and therefore changes in ecosystems.
4
•
A rising sea level, associated with global warming at various times
in the geological history of the Earth, not only reduced the amount of
land available for occupation by terrestrial species, it also resulted in
climatic changes in different parts of the planet.
•
The movement of the Indo-Australian plate north, after it broke from
Antarctica, brought about temperature and rainfall changes in the
Australian landmass, but also changed ocean currents, which in turn
probably also led to further climatic change.
Evolution of Australian biota
These changes normally led to complete destruction of habitats to which
the existing species were adapted, leading to their extinction. The few
species which did survive these events became the ancestors for a further
radiation of new species.
It has been estimated that the evolution of new species to fill such
modified ecosystems was normally quite slow. For example, after the
mass extinction at the end of the Permian period it took at least six
million years for the species diversity to return to anywhere near what it
had been before the extinction event.
The mass extinction of species at the same time as the dinosaurs at the
end of the Cretaceous period was probably not due to the factors
discussed above but to the effect of large meteorite impacts, such as that
at the Chicxulub crater on the Yucatan peninsula of Mexico, which is
200 km across! It is suggested that such impacts drove so much dust into
the atmosphere that it reduced the amount of sunlight reaching the Earth
and severely reduced photosynthesis throughout the ecosystems.
It is also possible that the impact also triggered volcanic eruptions by
causing movement of tectonic plates. The ash from these eruptions
further reduced light penetration from the sun.
All of these extinctions however, were not something that just happened
overnight. Even in the Cretaceous extinction, the elimination of species
was thought to be fairly slow, lasting up to at least 100 000 years.
Specialisation and extinction
Species which evolve into a specialised way of life are thought to be
more prone to extinction than those that have more general adaptations.
The megafauna may have been dependant on specific attributes of their
environments and were unable to cope with changes to these
environments brought about by climate change.
The platypus is highly specialised to obtain its food from the bottom of
water bodies using its bill. The modern species must obtain all of its
food in the water and so is very susceptible to any environmental changes
which might reduce the amount of aquatic habitat. The other fossil
platypus species may have become extinct as a result of arid conditions
increasing over their distribution.
Part 6: Evolution, survival and extinction
5
Extinction due to human activity
Since modern humans evolved, a sixth mass extinction of species has
been in progress due to a number of human activities, including:
•
hunting for food, animal products (eg. furs) and for sport
•
pollution – especially water pollution, which has eliminated many
susceptible species
•
introduction of predators, diseases and competitors
•
climate change – mainly due to the greenhouse effect and global
warming
•
habitat destruction for agricultural land, plantation forests and urban
development.
You are almost certainly aware that carbon dioxide and other gases in the
lower atmosphere permits the Sun’s heat to reach the Earth but prevents
some of it from being re-radiated back into space. Without this
greenhouse effect the average temperature on the Earth would be several
degrees lower than it is now and some species would be unable to
survive. However, the burning of fossil fuels, and a number of other
human activities, are increasing the amount of these gases in the
atmosphere, enhancing the greenhouse effect. As a result of this global
warming is occurring.
There are a few scientists who still are unconvinced by the evidence that
global warming is occurring, but the idea is generally accepted by the
majority of scientists. The world body of scientists called the
Intergovernmental Panel on Climate Change (IPCC) concluded that the
rate of warming at the present was unprecedented. They also found that
the rate matched the model for the enhanced greenhouse effect.
The prediction is that sea levels will rise by 7 metres over the next
thousand years.
While most scientists would agree with the findings of the IPCC report
there is much less agreement about what climate and sea level changes
will result from global warming. Increased global warming is happening
as a result of human activity but what sea level and climatic change it
will lead to in the future, and how far off these changes will be
experienced, is much less definite.
Scientific knowledge of changes in climate, habitats and the diversity of
species occurring in an area have been deduced in various ways by
scientists, including palaeontologists, climatologists and geologists.
But, predictions from these data need to be made with extreme caution
due to the incomplete nature of the data. Remember that humans have
only been around for the last 100 000 years and for a good deal of that
6
Evolution of Australian biota
time they did not have the technology either to measure the data or to
record it.
Wild species of organisms, which are not yet extinct, but occur in small
numbers or in restricted habitats are often given conservation
descriptions like threatened, endangered or vulnerable. These are species
which have not had suitable genetic variations in their populations which
have permitted some individuals to survive and reproduce in the face of
the rapid changes brought about in their environments by the activities of
humans. Any climatic changes, brought about by global warming, have
the capacity to affect the status of such species and so predictions of what
will happen to the climate in various parts of the world are important
from the point of view of their conservation.
Species of organisms used for food by humans will also be affected by
climate change. Various complex climate models suggest that some
areas of the world, which are now well supplied with rainfall, will
become arid and some arid areas will be well supplied by rainfall.
This is predicted to have a major impact on some of the current food
producing areas of the world. At present we know that even weather
forecasting from day to day is quite imprecise and so longer range
predictions using these climate models are at best quite speculative.
It is a sobering thought that, even if the extinction brought about by
human activities were to cease now, the descendants of the modern
humans responsible for this extinction would probably not witness a
recovery. It has been estimated that recovery from previous mass
extinctions has taken millions of years. As the average length of time
any species has lasted from its evolution to its ultimate extinction is only
between one and ten million years, it seems likely then that Homo
sapiens will itself have become extinct before the recovery of diversity
has occurred!
In Parts 2 and 3 of this module you considered that climate, geology, habitat
and changes in flora and fauna over geological time need to be deduced or
inferred from indirect evidence. You will need to go back through your
notes to find this information. This will be good revision and will also help
you with the self test at the end of this part of the module.
1
Choose one period of geological time since Australia split away
from Antarctica and describe the climate, sea level, geology and
flora and fauna of the period.
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
Part 6: Evolution, survival and extinction
7
2
Describe two pieces of evidence scientists may have used to work
out what the conditions would have been like at that time.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
3
Greenhouse conditions resulting in global warming have occurred
previously in the geological history of the Earth. One reason for this
is thought to have been slight changes in the Earth’s axis and another
the greenhouse gases being released from increased volcanic activity
at various times. However, the latest global warming is thought to
be due to human activity.
Outline one method which scientists may have used to work this out.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Check your answers.
8
Evolution of Australian biota
Evolution, survival and extinction
The last thylacine or Tasmanian tiger, Thylacinus cynocephalus, was
captured in 1933 and died in captivity in 1936. This large carnivorous
marsupial once occurred on the mainland of Australia, as well as in
Tasmania and Papua New Guinea, but became extinct in all but
Tasmania around 2000 years ago.
Thylacine.
The Tasmanian tiger was not a fast runner and hunted at night in pairs,
tiring its prey by relentless pursuit, before killing it with a powerful bite.
Since kangaroos and wallabies were its main source of food it inhabited
open forest and woodlands.
Being at the top of the food chain the species probably did not occur
in large numbers. Numbers were reduced by human hunting (it
unfortunately developed a taste for sheep as food!) and possibly by an
outbreak of disease.
The species became extinct in other parts of Australia, probably as a
result of competition with the dingo, introduced into Australia around
3500-4000 years ago by Asian sailors. There are no dingos in Tasmania,
which became separated from the Australian mainland between
8 000 - 10 000 years ago.
Part 6: Evolution, survival and extinction
9
If you think about the evolution, survival and extinction of this species of
marsupial then you may draw the following conclusions.
•
The thylacine must have evolved from some marsupial ancestor after
Australia broke away from Antarctica.
•
During the changes in climate, as Australia drifted north, the new
species evolved to be adapted to the role of ‘top’ carnivore in the
woodland ecosystems, which arose as a result of the drying of the
continent.
•
However, no individuals in thylacine populations had the genetic
make-up necessary for the species to adapt to:
–
the competition from the introduced dingo on the mainland,
–
the hunting pressure from humans in Tasmania
–
some deadly disease organism.
Like more than 99% of species which have evolved on Earth, the
thylacine became extinct. But, it was helped along the way by human
intervention by the introduction of a new competitor, hunting and
possibly the introduction of a disease not normally found in Australia and
one to which some animals had no natural resistance.
Do Exercise 6.1.
10
Evolution of Australian biota
Summary
Now attempt the self-test, which will test a range of learning material and
skills which you have covered in this module.
Before starting on this exercise, read back through your notes and
assignments to familiarise yourself again with material which perhaps
you have not looked at for some time.
Multiple choice
1
2
The concept of the environment favouring the survival and
reproduction of the most adapted features or the elimination of the
least adapted was proposed by:
A
Charles Darwin and Thomas Huxley.
B
Thomas Huxley and Bishop Wilberforce.
C
Alfred Wallace and Charles Darwin.
D
Alfred Wallace and Thomas Huxley.
On his visit to Australia on the HMS Beagle Charles Darwin is often
said to have been uninterested by the flora and fauna of this country.
Which statement is the best interpretation of Darwin’s experience
with the flora and fauna of Australia?
A
Darwin was unable to identify most of the species and so took
little interest in them.
B
Darwin carried out considerable collecting and although
naturalists before him had already identified many species, he
also found new ones.
C
Darwin was very interested by the geology of Australia but paid
little attention to its flora and fauna.
D
Darwin watched platypuses swimming in the Coxs River near
what is now Lithgow, but apart from that, he saw few of
Australia’s native species.
Part 6: Evolution, survival and extinction
11
3
4
5
12
More than half of the land area of Australia is said to be arid.
Which statement is the best definition for arid conditions?
A
An environment where rainfall is very low and evaporation is
very high.
B
An area with hot but humid conditions
C
A hot, windy and dusty environment.
D
An environment which is always has low rainfall and high
temperatures.
There are two types of cell division, one involved with growth,
repair and asexual reproduction and the other strictly with sexual
reproduction. Meiotic cell division results in the formation of:;
A
two daughter cells which are genetically different from each
other
B
four daughter cells with half the genetic complement of the
original cells
C
four daughter cells which have fairly similar genetic make-up
D
two daughter cells which are genetically identical to each other.
The giant southern landmass of Gondwana consisted of the
following tectonic plates:
A
African, South American, Indo-Australian and Pacific
B
Indo-Australian, Antarctic, African, South American
C
Antarctic, Pangaean, Indo-Australian and South American
D
African, South American, Pangaean and Pacific.
Evolution of Australian biota
Short Response Questions
6
The following have been used as evidence that Australia was once
part of a single large southern continent.
•
continental margins
•
spreading zones between continental plates
•
fossils evidence
•
similarities between modern and fossil species
Choose two of these and briefly explain how they show a
relationship between the past and present landmasses.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
7
Scientific study has led to a better understanding of the biology of
many species of organisms in Australia. Use an example you have
studied to answer the following questions.
a) Describe an Australian species which has become better
understood as a result of the use of modern technology.
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
Part 6: Evolution, survival and extinction
13
b) Briefly describe the technology used to determine the nature of
this adaptation.
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
8
After Australia broke from Antarctica it drifted north and
experienced considerable climatic and geographical change. During
this time new species evolved as a result of the following factors.
•
genetic variation
•
habitat changes
•
isolation and
•
natural selection.
Use these factors in a description of proposed steps which take place
in the formation of a new species.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
9
In your studies you investigated variation within two species.
a) Name one of these species and state what variable characteristic
you decided to measure.
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
14
Evolution of Australian biota
b) Describe how you went about measuring this characteristic,
including how many individuals you measured.
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
c) Present your results either as a table of values or as a graph
showing the distribution of different measurements.
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
Check your answers.
Part 6: Evolution, survival and extinction
15
16
Evolution of Australian biota
Suggested answers
Mass extinctions
1
The Miocene period in Australia was thought to have been wet and
to have varied in temperature between being hot and cold, with
rainforests dominated the region. However, by late in the period
species in the Eucalyptus and Casuarina genera were beginning to
be more common. Mammals and birds dominated the vertebrate
fauna, probably including aquatic forms such as several
platypus species.
2
Fossils. For example, a sequence of fossilised leaves or pollen from
rainforest and then Eucalyptus plants would indicate wet and then
drier conditions. Fossils of parts of such species as platypus, turtles
and water birds indicates a past aquatic environment.
Higher growth rates seen in tree rings at the start of the period
indicate wet conditions and drier later.
3
Air trapped in ice cores indicate higher levels of carbon dioxide
since the start of the Industrial Revolution than previous years.
Growth rings in trees can also be used as plant growth increases with
increased carbon dioxide in the atmosphere.
Summary
1
C
Darwin and Wallace came up with the idea of natural selection
independently of each other at about the same time.
2
B
Darwin expressed the thoughts in a letter that there would be
few new species which had not been identified by naturalist who
had visited Australia before him but also carried out his own
collecting and described new species.
3
A
Although all of Australia’s arid areas are also hot in summer,
conditions are often cold in winter, and in other areas of the
world arid conditions can be cold and dry.
Part 6: Evolution, survival and extinction
17
4
B
The genetic material in the daughter cells (gametes) is halved by
the second division during meiosis.
5
B
Gondwana included India and Australia (Indo-Australian),
South America, Africa as well as Antarctica.
6
The margins of continents, especially the continental shelves and
rock strata show good fit between parts of the continents which are
now separated, suggesting that they were once joined.
The existence of spreading zones between plates provides evidence
that the plates are in fact moving in relation to each other.
Fossils of similar groups, like the marsupials and early plants, such
as species of Glossopteris have been found on other southern
continents, suggesting that they got there when the continents were
initially joined to each other.
Living species, such as the flightless ratite birds (emus and
cassowaries in Australia, rheas in South America, the extinct
elephant birds of Africa and the kiwi and extinct moas of
New Zealand), suggest that they evolved before the break-up of
the supercontinent.
7
a) The platypus was thought to be like a reptile and was not able to
regulate its body temperature. However, measurements of body
temperature in captive and free-ranging platypuses enabled
scientists to discover that it did regulate its body temperature,
enabling it to survive in the cold conditions found in much of its
range in winter.
b) Radio telemetry was used in these studies where a transmitter
measuring body temperature was attached to animals and the
signal picked up by a receiver on the river bank.
8
As conditions change, many individuals do not have genetic
variations which adapt them to the new conditions. As a result most
become extinct but those have a suitable genetic make-up survive
and reproduce. Their offspring are adapted to the new conditions
and so these characteristics are passed on to the next generation.
If the group of organisms is isolated from other groups of the same
species this process of natural selection may quite quickly lead to the
formation of a new species.
9
a) Number of striped periwinkles with stripes of varying widths.
b) 20 individuals in each of 3 stripe classes were measured using
vernier callipers.
18
Evolution of Australian biota
c)
Stripe category
wide stripes
Frequency (numbers of
individuals in the sample)
3
(> 2 mm wide)
medium stripes
25
(1-2 mm wide)
narrow stripes
2
(< 1mm wide)
Part 6: Evolution, survival and extinction
19
20
Evolution of Australian biota
Exercises - Part 6
Exercises 6.1
Name: _________________________________
Exercise 6.1: Extinction
Choose one or more species of Australian animal or plant which has
either become extinct throughout Australia or has reduced its previous
distribution in Australia. Find out the following:
•
Which group the organisms belongs to and therefore what might
have been its ancestral group.
•
Its adaptations to the habitat in which the organisms was found.
•
The changes in the organism’s ecosystem to which the population
has been unable to adapt and which have led to its extinction.
To do this you will need to consult a range or sources, including the
Internet (if you have access to it) CD ROMs, library books and
magazines, such at Australian Geographic and Nature Australia
(published by the Australian Museum). You may also choose to use the
information in this part.
a)
Outline reasons for the extinction of at least one Australian species.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
b) Describe the adaptations that assisted the survival of at least one
Australian species.
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 6: Evolution, survival and extinction
21
c)
Name one Australian species that has become extinct.
Propose reasons for the extinction of this organism.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
22
Evolution of Australian biota
Student evaluation of the module
Name: ______________________
Location: ____________________
We need your input! Can you please complete this short evaluation to
provide us with information about this module. This information will help
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1
Did you find the information in the module clear and easy to
understand?
_____________________________________________________
2
What did you most like learning about? Why?
_____________________________________________________
_____________________________________________________
3
Which sort of learning activity did you enjoy the most? Why?
_____________________________________________________
_____________________________________________________
4
Did you complete the module within 30 hours? (Please indicate the
approximate length of time spent on the module.)
_____________________________________________________
_____________________________________________________
5
Do you have access to the appropriate resources? eg. a computer, the
Internet, scientific equipment, chemicals, people that can provide
information and help with understanding science
_____________________________________________________
_____________________________________________________
Please return this information to your teacher, who will pass it along to the
materials developers at OTEN – DE.
BIO.Prelim 43211 Evolution of Australian biota
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