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Population and Community structure
Species: a group of organisms which share the same
characteristics and
are capable of interbreeding
Population: a group of organisms of the same species which live in the same
habitat so that random interbreeding takes place
Community: all the plants and animals living in a defined area
Ecosystem: the study of living things and their relationship to each other and
to the environment
Ecology: the study of living things and their relationship to each other and to
the environment
Ecological niche: the functional position of an organism in its environment
Environmental resistance: the combined effect of all the limiting factors that
limit the growth of a population
Limiting factor: factors (density dependent or density independent) that limit
l
the rate of population growth
1.Use the following
diagram to list:
1.1 A few species
1.2 A population
1.3 A community
2. What kind of
ecosystem is
illustrated
here?
Natality: the birth rate. It’s the production
of new individuals by birth, hatching,
germination or division.
Mortality: the death rate.
Immigration: the process that occurs
when an organism enter a new place to
settle permanently
Emigration: the process that occurs when
an organism leaves one place to go and
live in another place
Migration: a group of birds, or other
animals that are moving together from
one region or country to another to avoid
harsh environmental conditions.
Population size
Factors affecting population size
Migration of zebra and wildebeest in the Serengeti
Yearly migration of wildebeest in the Serengeti.
Migration is most common amongst birds, mammals
and some insects (monarch butterflies)
Wildebeest migration: migration is a response to
seasonal change. The function of migration is to keep
animals in a suitable environment throughout the year.
Migration of birds: If habitat quality declines, animals
improve their chances of survival and reproduction by
going elsewhere
Migrating swallows: Animals appear to
anticipate the changes in season.
The relationship between species, populations
community and the ecosystem
Carrying capacity is the maximum population size a certain
environment can support for an extended period of time, for a
population of a particular species.
Under ideal conditions, a population naturally increases until it
overshoots the carrying capacity. At this point, the environment
can no longer provide for the species, due to a number of
different environmental resistances, including food, crowding,
competition, etc. The population, due to lack of resources, will
begin to die out, allowing the environment to recover. As the
environment recovers, the species population is able to flourish
once more. This leads to a fluctuation between the prosperity of
the species and the prosperity of the environment (hence the
fluctuations in the graph).
Carrying capacity
If a population reaches
carrying capacity it can
remain stable or move
up and down (fluctuate).
If there is more rainfall
and more food available
the carrying capacity
increases and the
population will increase
until it reaches the new
carrying capacity before
it levels off again. If
there is habitat
destruction or a draught
the carrying capacity
decreases and the
population will decrease
until it reaches the new
carrying capacity and
levels off again.
Carrying capacity of rabbits in a specific area
1. What does the blue
line represent? What
does the purple line
represent? What does
it mean when the
purple line rises above
the blue line?
2. Which of the
following situations
might cause the purple
line to decrease below
the blue line: abundant
food sources, lack of
competition, a young
population, or plentiful
roaming space?
3. Can you think of any
events that would cause
the purple line to stay
above the blue line
indefinitely?
Question: Carrying capacity
1.1 Suggest THREE reasons why the growth form between the period 1920 and 1935 is as it is.
1.2 What is the growth phase called between 1910 and 1920?
(1)
1.3 During which year did the jackal enter the fenced area? Give a reason for your answer from
the information supplied.
(3)
1.4 Between 1940 and 1950 the springbok population increased again. Mention a possible reason
for this increase.
(2)
1.5 Mention FOUR other factors, besides the jackals, which could have caused the decline in the
springbok population between 1935 and 1940?
(4)
1.6 What method was most probably used to determine the size of the springbok population? (1)
1.7 Do you think the line representing the carrying capacity is accurate?
Give a reason for your answer.
(3)
1.8 The population between 1965 and 1975 appears to have stabilised. Suggest how the farmer
might be controlling the population.
(2)
1.9 What do you notice about the growth from 1915 – 1925 and 1940 – 1950?
(1)
(20)
Density dependent and factors
Density dependent
Density independent
a density-dependent factor affects a
greater percentage of individuals in a
population as the number of individuals
increases; it will also affect each
individual more strongly. Population
growth declines because death rate
increases, birth rate decreases or both.
Resource limitation is one such density
dependent factor. A reduction in
available food often limits reproductive
output as each individual produces
fewer eggs or seeds. Health and
survivorship also decrease as crowding
results in smaller, less robust individuals.
Many predators concentrate on a
particular prey when its population
density is high, taking a greater
percentage than usual.
Density-independent factors affect the
same percentage of individuals
regardless of population size. Weather,
climate and natural disasters such as
freezes, seasonal changes, hurricanes
and fires are examples; the severity and
time of occurrence being the
determining factor on what number of
organisms is affected. In some natural
populations, these effects routinely
control population size before densitydependent factors become important
Geometric growth form (J- curve)
Logistic growth form (S-shaped curve)
Question : growth patterns
•
4. A certain fast growing unicellular micro-organism is cultivated in a sugar solution in a
closed test tube at 250 C. At regular intervals, samples were taken in order to calculate the
population size. The graph below was drawn from the data obtained. Study the graph and
answer the questions that follow.
•
•
•
•
•
•
•
•
•
•
•
4.1 Which specific organism was most probably cultivated in the test tube?
(1)
4.2 Name the growth phases indicated by A, B and C respectively.
(3)
4.3 Give an explanation for the specific growth pattern of each of the phases A,
B and C.
(6)
4.4 What is phase Y called and what is the possible cause, thereof, for this specific
population in particular?
(3)
[ 13 ]
Comparison between geometric (J-curve) and Logistic (S-curve)
Methods to determine population size
1. Direct method: census
A pitfall sampling method can also be used
Methods to determine population size
2. Indirect method: simple sampling
Simple
sampling can
be used to
determine the
number of
plants in an
area
Quadrat sampling method for
plants
In simple sampling a physical count of all the
animals/plants under investigation in a small
sample are of the habitat is done.
The total population in the big area is calculated
as follows:
Estimate number of = number of individuals in sample x habitat size
individuals in the
__________________________
population
sample size
Activity 1: simple sampling
Method
Mix an unknown number of tiny beads with sea sand thoroughly to fill a 500 ml jar.
Remove a level teaspoon (5 ml) of the mixture from the jar.
Spread the mixture on a saucer and count the number of beads.
Use the formula below to estimate the total number of beads in the bottle :
Total nr. of beads = nr. of beads in sample x total volume of mixture (500 ml)
____________________________
volume of teaspoon (5ml)
Investigation Total
Place the bead and sea sand mixture back into the jar.
population
Mix thoroughly and repeat the exercise a few more times.
Obtain an average estimate of the number of beads in the jar
1
Results
2
Complete the table :-
3
Questions
1. Why is it necessary to repeat the
investigation a number of times?
2. How is this investigation limited?
4
5
Ave
estimate of
beads/jar
Simple sampling can be used to determine
the number of micro organisms on a slide
Question : Simple sampling
A leading Kwa-Zulu entomologist ( a person that studies insects )
decided to work out the number of worms that occurred in
Kwa-Mashu. The total area in Kwa Mashu where the worms
occurred was 2000 m2. He chose five 10 m2 plots and found
120, 100, 150, 130 and 100 worms in each plot respectively.
(i)
Estimate the total number of worms in the Kwa-Mashu area.
(Show ALL calculations).
(5)
(ii)
Describe two ways how the entomologist could improve the
reliability of these results.
(2)
(7)
Answer : Simple sampling
Ave. number of worms in a plot = 120+100+150+130+100 =
600
5 plots
= 120 worms/plot
Estimate number of = number of individuals in sample x habitat size
individuals in the
__________________________
population
sample size
=
120 x 2000m
10m
= 24 000 worms
Methods to determine population size
2. Indirect method: mark recapture
A number of
animals are caught
and marked
In theory, mark / recapture techniques involve
sampling a population of animals and then marking all
of the individuals captured in a recognizable way. The
marked animals are then released back into the
population and left to mingle for a suitable period of
time. Once they have become thoroughly mixed into
the population again, the population is re-sampled.
The assumption is then made that the proportion of
marked animals in the second sample is the same as
the proportion of marked animals to non-marked
within the whole population. Enough time must be
allowed to elapse for complete mixing to have
occurred.
The same method are used with fish
The fish are marked – but don’t take
them out of water for too long!
The following should be taken into account
when animals are caught and marked
1. The animal usually needs to be captured to be marked, the animal should not be injured and
its behaviour pattern should not be altered.
2. The mark used should not harm the animal - for example a dot of a particular paint may turn
out to be toxic to the animal. Trials therefore need to be done to ensure that the animal is
not harmed in any way.
3. Take random samples from the population. If you take samples from only one place each
time, they you are likely to catch the same animals that you released.
4. Once you have released the first sample, give the animals enough time to mix randomly with
the rest of the population before you take the second sample.
5. Ensure that animals do not become 'trap-shy' and avoid the traps after the first capture. This
can be reduced as far as possible by choosing a method which will not distress the animal
unduly. Some animals may become 'trap-happy', particularly if the traps are baited. This can
be overcome by setting out the baited traps, without actually trapping, for some time before
the first sample is taken. This allows all animals in the population to become equally traphappy before you start.
Trap-shyness results in population overestimates, while trap-happiness results in population
underestimation
They are released back into the water and some
are caught again after a period of time
The mark-recapture method can also
be used on frogs
The mark-recapture method can also
be used on crabs
Activity 2: Mark -recapture
Method:
1. Get into groups of 4.
2. Tear old papers (newspaper/unused notes) into small pieces and throw into a
container. The container will represent a dam and the paper pieces fish. You
should have ± 100 - 200 fish in your dam.
3. Mark 30 of your fish with a pen. Discuss how you should mark real fish.
4. Put the marked fish back into your dam and mix them up with the rest of the
fish.
5. Take a handful of the mixed fish out of the dam. Count the marked and the
unmarked fish.
6. Estimate the size of your fish population by using the formula:
Population size

number in the first sample x number in the sec ond sample
number of marked individuals in the sec ond sample
7. Repeat your estimate at least 5 times and calculate the estimated average
fish in your dam. Tabulate your results.
8. List possible shortcomings of your investigation
Trend in the human
population growth up to 1650
and from 1650 to the present
moment
It is evident from the graph that :1. the human population is increasing rapidly and shows a geometric (J-shaped)
growth form
2. the population is doubling in shorter periods
3. the next doubling period (8 000 million) has been calculated to be in the year 2010
– a doubling period of 35 years
4. this increase in population CANNOT go on indefinitely – as environmental resistance
(shortage of food, O2 and living space) increases – something has to give – unless we
are able to stabilise the population at the carrying capacity of the world
Worldwide
human
population
growth
from 1750
to 2000
Human population growth according to History
Human population growth in SA from
1947 to 2011
Human population age and gender
distribution in:
1. an increasing population
A population pyramid with a small number of old people
indicates a population with a high birth rate, a high death
rate and a short life expectancy. This pattern is typical of
less economically developed countries (LDC) like South
Africa, South America and Asia (excluding Japan)
2. a stable population
There is approximately the same number of young people
and old people. About the same number of children is born
each year compared to the number of people who die
each year. Economical developed countries like Ireland
have this kind of pyramid
3. a decreasing population
There are more old people than young people. Each year
more people die than are born. Developed countries like
Germany have this kind of pyramid. Some southern African
countries, like Botswana (experiencing the effects of
HIV/AIDS) are also starting to show this kind of age-gender
pyramid.
Population sizes in different parts of the world
The graph is divided into 2 groups:
1. The less developed countries (LDC) like Latin America, Africa and Asia (excluding
Japan). Population growth is expanding rapidly and the majority of people live in
poverty. Medical care and technological advances are not readily available, food is
scarce and levels of education are low. A high social value is placed on large families.
2. The more developed countries (MDC) like North America, Australia and Europe.
Population growth is low and people enjoy a good standard of living. Medical care and
technology is readily available. Food and technology are available, level of education is
high.
A comparison of
less developed
countries with
more developed
countries
Discuss the differences
between the gender-age
pyramids for Japan &
Zimbabwe.
Use these graphs to discuss the changing trends in
the SA population. Indicate the working group (20
– 60 years), mention how their economical
contributions will support the non-economical
groups (children and old people). Take the % of
jobless people into consideration and the fact that
only 5.6% of the population pays tax
The effect of high population growth on the environment
The effect of high population growth on the environment
(depletion of resources and increased pollution)
The effect of a growing population on resources,
pollution, industrial output and the availability of food
Ecological footprint: the impact of a person, city, or
country on the ecology of a local area or the whole planet.
It is a measure of how much land and water a person, city
or country needs and the wastes that are produced.
We do not know what the carrying capacity of
the world is. The United Nations has predicted a
global human population of over 10 billion
people by 2050 – therefore an estimated 4
billion people will be added to the population in
the next 40 years.
One approach to estimate the carrying capacity
of the earth is to look at the ecological footprint
of different groups of humans.
• According to the Global Footprint Network, humanity uses
the equivalent of 1.3 planets to provide the amount of
resources we consume and absorb the waste we produce.
This means it now takes the Earth one year and four
months to regenerate what we deplete in a year.
To calculate the ecological footprint of a population all
their needs need to be taken into account, e.g. food,
water, fuel, building materials, clothing and medical
care. The impact, to produce the needs, on the
environment is then calculated. An ecological
footprint represents the area of land and water
utilised by a particular nation. It takes into account
the resources used by wastes produced by that
country. It measures how much land an water a
human population requires to produce what it
consumes, and to absorb its wastes using current
technology. It compares human demand with the
earth’s capacity to regenerate
In 2006, the global ecological footprint outpaced the Earth’s biological capacity by 30
percent. This trend is increasing. In fact, on September 23rd of this year, we passed
“Overshoot Day,” the day the human ecological footprint exceeded the Earth’s
biocapacity and began living beyond its ecological means. Since then, we have been
engaged in the ecological equivalent of deficit spending: our rate of resource
consumption is exceeding the rate at which those resources can be naturally
replenished.
What are we doing?
Activity 3:Use the next two slide to complete the
table:
Greater ecological
footprint than South
Africa
Similar ecological footprint Smaller ecological
to South Africa
footprint than South Africa
Australia
Ethiopia
India
The effect of high population growth on the environment. The
darker the colour, the greater the ecological footprints.
Reckless consumption is depleting the world’s natural capital to a
point where we are endangering our future prosperity. The Living
Planet Index shows that over the past 35 years along the Earth’s
wildlife populations have declined by a third.
Yet our demands to continue to escalate, driven by the relentless
growth in human population and in individual consumption. Our
global footprint now exceeds the world’s capacity to regenerate by
about 30%. If our demands on the planet continue at the same rate,
by the mid-2030s we will need the equivalent of two planets to
maintain our lifestyles.
The ecological credit crunch is a global challenge. The Living Planet
Report 2008 tells us that more than three quarters of the world’s
people live in nations that are ecological debtors—their national
consumption has outstripped their country’s biocapacity. Thus, most
of us are propping up our current lifestyles, and our economic
growth, by drawing (and increasingly overdrawing) upon the
ecological capital of other parts of the world.
The following categories affect your ecological footprint:
Ecological “footprint" for different countries
It is likely that the countries
and regions with surplus
ecological reserves, and not
the ones relying on continued
ecological deficit spending,
will emerge as the robust and
sustainable economies and
societies of the future.
•To support my lifestyle, it takes 15.4 acres of the Earth's productive area.
What will happen if this trend continue?
What can you do to save the
world?
Sustainable: careful use of natural and human
resources so that they will also be
available to future generations
Conservation: the management of the Earth’s
resources so that it yields the
greatest sustainable benefit to future
generations while maintaining its
potential to meet the needs of future
generations
Human demands versus conservation in the
harvesting of natural resources
Abalone poaching is illegal
Human demands versus conservation in the harvesting of
natural resources
Oysters need to be a specific size before it may be harvested
Human demands versus conservation in the harvesting of
natural resources
During 2010 more than 300 rhino’s have been pouched and killed for
their horns in South Africa. The sad truth is that a rhino is worth more
dead than alive. A rhino horn is valued at $20 000 (R14 000) per kg
and a rhino horn weigh up to 5 kg. Currently a live rhino is sold at
R130 000 – R300 000.
Social organisation enhance survival of species
Animals that live in herds, schools, swarms, and flocks
typically give up on their individual defences because they
pursue another survival strategy. If you are a member of a
herd, you do not need to run faster than your predator;
you only need to run faster than the slowest member of
your herd. The individual defence IS forming the herd
where the weak are daily sacrificed to earn the others
one more day of untroubled life, until it is their turn. It is
creepy to watch video footage of lion hunting the
antelopes: after a brief chase, the herd is standing still
and staring at their member being eaten alive, chewing
their cud. That's what herd is about.
Herds of wildebeest
School of fish
Some Predators form packs as an
efficient hunting strategy like wild dogs
African wild dogs form packs of up to 40 members, each with a dominant breeding
pair that remain monogamous for life. These gregarious animals are co-operative
hunters, relying on sight rather than smell to pinpoint their prey. Hunts tend to occur
at dawn and dusk, but on occasion the dogs will venture out if there is a full moon.
They chase until their prey tires, reaching speeds up to 55 kmph, and
sometimes disembowelling prey while it is still running
African wild dogs live in packs of 6 to 20. The aggression exhibited towards prey is
completely nonexistent between members of the pack and there is little intimidation
among the social hierarchy. Their large range of vocalizations includes a short bark of
alarm, a rallying howl and a bell-like contact call that can be heard over long distances.
Elaborate greeting rituals are accompanied by twittering and whining. The entire pack
is involved in the welfare of the pups, which are born in thick brush or in a den.
Sharks also
hunt in
groups
Group hunting improves efficiency. By hunting
in groups a predator can kill larger animals than
a single animal can kill
Animals with
dominant
breeding
pairs- the
giant otter
Giant otters live in
groups with one
breeding pair. There
is one dominant
female in the group
She has many
offspring and is also
the top fish catcher
and the leader of the
hunt.
Animals with dominant
breeding pairs – Lions
The advantages of dominant
breeding pairs are:
- offspring are cared for by
many members of the group
- dominant males and females
are usually the strongest and
most efficient members of the
group, their genetic material
will be carried to the next
generation
The Southern ground-hornbill occurs
from Kenya to southern Africa, living
in a wide range of grassland, savannah
woodland habitats. In South Africa, it
is listed as Vulnerable, with an
estimated population of just 15002000. It eats a wide range of food,
especially animals, such as
grasshoppers, frogs, mongooses and
bird nestlings. It is a monogamous,
cooperative breeder, with a group
consisting of a dominant breeding
pair and 0-9 helpers, who are usually
either adult males, or juveniles from
previous breeding seasons. It lays 1-2
eggs, which hatch in the sequence
laid, meaning that the one chick is 314 days older than the other chick.
The younger chick is unable to
compete for food with its older
sibling, and dies of starvation when it
is rarely 3-4 weeks old. Current
conservation measures include handrearing of the otherwise redundant
second born chicks, captive breeding
and reintroduction.
The Southern ground hornbill
Dominant breeding pairs - meerkat
Meerkats are facultative
monogamous, which means
that they breed with only
one other member of the
opposite sex. The female
does not depend on the
male for help raising the
pups. She depends instead
on kin and non-kin helpers.
Cooperation in meerkat
breeding is obligate because
the breeding female cannot
reproduce and raise
offspring without help.
Subordinate meerkats
occasionally breed, but the
dominant pair is always
responsible for the majority
of reproduction.
The alpha pair mates for life, though life span is limited by predation.
Turnover in the dominant male position is higher than in females because
males are more likely to leave the territory, and meerkats off of their territory
are likely to be preyed upon. The mating pair shares little or no relatedness
Availability of resources limits meerkat breeding. Rainfall triggers breeding
because rain increases plant life which in turn increases the population of
arthropods that serve as meerkats’ prey. In fact, reproductive success for a band
as a whole depends directly on the amount of rain during the rainy season
Because rainfall is unpredictable, breeding meerkats must have a mate at all
times so that they don’t miss any breeding opportunities. If they had to spend
part of the rainy period wooing a mate, they would run the risk of breeding too
late into the season. The rain and the corresponding increase in arthropod
abundance would end before the critical period of offspring growth, or even
before the birth of the offspring. Reproduction also depends on the presence of
helpers. Meerkats are monogamous because there are only enough helpers for
one litter. With only one litter, there can be only one breeding female, and
competition for the position results. The breeding female has her choice of
males, and she chooses the one with the best genes. He proves himself to her
by competing for and attaining the alpha male position.
There is one queen to each
colony, and she is much larger in
size than the other bees. Her
main task is to lay eggs.
Reproduction can take place
only by means of the queen, and
no other females are able to
mate with the drone males. In
addition to laying eggs, the
queen also secretes important
communicative substances that
maintain the unity of the colony
Honey bee eggs hatch regardless
of whether they are fertilized.
Drones develop only from
unfertilized eggs. Unfertilized
eggs are haploid in origin, which
means that they contain only 16
chromosomes from their
mother. Honey bees are a haplodiploid species, in which drones
have haploid cells and workers
and queens have diploid cells
Bees live in a colony with
division of labour
The drones are larger than the female
workers, though they lack stings and the
necessary organs to collect food for
themselves. Their only function is to
fertilize the queen.
The worker bees perform all such other tasks
that you might imagine, including making the
waxen combs in the hive, gathering food,
producing royal jelly, regulating the
temperature in the hive, cleaning it of debris
and defending it
Identify the different members of a bee colony:
The workers (females) collect
pollen and nectar every day
Some pollen collect in a packet
around their legs
Nectar
and pollen
is stored
as honey
Honey is stored to feed the
developing embryos
Developing larvae: responsibility for caring for the
larvae falls to the worker bees in the hive, which
prepare incubation cells in a region specially set
aside in the combs where the queen can lay her
eggs
Worker bees feed the newly-hatched larvae with great care and selflessness. In fact, it
has been established that worker bees will visit any single larva some 10,000 times
during its period of growth. For the first three days after they hatch, the larvae are fed
on royal jelly. During this larval stage, the young bees are fed constantly and undergo
their greatest physical development. As a result of their regular feeding during this
phase, the larvae's weight increases by up to 1,500 times in only six days.
Workers have a special wagging dance with which they
communicate with other workers on the distance and direction
of food sources
Division of labour among members of a colony,
e.g. an ant colony
Sociality is more advanced in bees, ants, and termites. As a rule, only one
female (a queen) lays eggs in a colony, and numerous workers are sterile.
Workers are involved in other functions like construction, defence and
taking care of juveniles. They often have a division of labour and
corresponding morphological differences.
Termites
with
different
members
and
division of
labour
This picture shows some forms (casts) of termites. Social insects have very
complicated behaviour. Their success largely depends on coordinated
actions of many individuals. For example, leaf-cutting ants have
underground fungus gardens. Ants bring foliage to this garden and collect
fungus for food. This is insect agriculture!