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Chapter 5
Evolution of Biodiversity
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Dung of the Devil
1918-1920: Flu epidemic (Spanish flu).
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Caused by H1N1 (closely related to the 2009-2010 virus:
swine flu)
Extracts from the “dung of the devil” used 80 years previous for
the Spanish flu showed potential to fight the swine flu.
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20mill-100mill people die. 600,000 in the US
Found only in the tropical rainforests of Madagascar.
Of the most promising current candidates for new drugs, 70%
were first discovered in plants animals and microbes.
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Unfortunately many being lost to deforestation, agriculture,
and other human activities.
Earth is home to a tremendous
diversity of species
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We can think about
Biodiversity on three scales:
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Ecosystem diversity- the
variety of ecosystems within
a given region.
Species diversity- the variety
of species in a given
ecosystem.
Genetic diversity- the variety
of genes within a given
species.
p. 121
How many species?
• Species: a group that is distinct from other
groups in terms of size, behavior, or biochemical
properties and can interbreed to produce viable
offspring.
• The number of species in a given area is the
most common measure of biodiversity (the
quantity and variety within an ecosystem).
• Scientists have named about 2 million species
and approximate there are 5-100 million on
Earth. The accepted estimate is set at 10
million.
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Species richness- the number of species in a
given area.
Species evenness- the measure of whether a
particular ecosystem is numerically
dominated by one species or are all
represented by similar numbers of
individuals.
Community 1 has
Good evenness
Both have same richness
p. 122
Phylogenic Tree
How do you
determine
how closely
related two
species are to
the original
ancestor or to
each other?
Another example P.126
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Evolution is the mechanism
underlying biodiversity
Evolution- a change in the genetic composition of
a population over time.
Microevolution- evolution below the species level.
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Gives rise to diversity within a species.
Macroevolution- Evolution which gives rise to
new species or new genera, family, class or phyla.
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Gives rise to new species, genus, class, family,
etc.
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Creating Genetic Diversity
Genes- physical locations on chromosomes within each cell of an organism.
Genotype- the complete set of genes in an individual.
Mutation- a random change in the genetic code.
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First way that diversity is created.
Most mutations are detrimental.
Some mutations improve an organisms chances of survival and
reproduction.
Phenotype- the actual set of traits expressed in an individual.
Recombination-occurs as chromosomes are duplicated during meiosis and
mitosis.
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Second way diversity is created.
Piece of one chromosome breaks off and attaches to another
chromosome.
Evolution
• Occurs by 3 primary mechanisms:
• Artificial selection
• Natural selection
• Random processes.
Evolution by artificial and natural
selection
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Evolution by artificial selection- when humans
determine which individuals breed.
Evolution by natural selection- the
environment determines which individuals
are most likely to survive and reproduce.
Darwin’s theory of evolution by
natural selection
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Individuals produce an excess of offspring.
Not all offspring can survive.
Individuals differ in their traits.
Differences in traits can be passed on from
parents to offspring.
Differences in traits are associated with
differences in the ability to survive and
reproduce.
• Fitness:
Ability to survive and
reproduce.
• Adaptation: Traits that improve an
individual’s fitness.
All species produce an
excess number of
offspring. Only those
offspring having the
fittest genotype will pass
their genes on to the
next generation.
P. 128
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Evolution by Random Processes
Mutation- occur randomly and can add to the
genetic variation of a population.
Genetic drift- change in the genetic composition
of a population over time as a result of random
mating.
Bottleneck effect- a reduction in the genetic
diversity of a population caused by a reduction
in its size.
Founder effect- a change in a population
descended from a small number of colonizing
individuals.
P. 129
Speciation and extinction
determine biodiversity
• Allopatric speciation- when new species are
created by geographic or reproductive
isolation.
• River
changes
course, etc.
• Sympatric speciation- the evolution of one
species into two species in the absence of
geographic isolation, usually through the
process of polyploidy, an increase in the
number of sets of chromosomes.
Once they become
polyploid, they
generally can not
interbreed with their
diploid ancestor.
Four things that influence
the pace of evolution
Change in a species’ genotype
or phenotype such as an
adaptation.
Can take 100’s to millions of
years.
Average global rate of evolution
is approximately 1 every 3 million
years.
If a species can not adapt quickly
enough it will go extinct.
Evolution shapes ecological niches
and determines species distributions
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Range of tolerance- all species have an optimal
environment in which it performs well. The limit
to the abiotic conditions they can tolerate is
known as the range of tolerance.
Fundamental niche- the ideal conditions for a
species.
p. 135
Mix of all abiotic conditions
that is perfect for the
organism.
Limit of tolerance
Niches
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Realized niche- the range of abiotic and biotic
conditions under which a species lives. This
determines the species distribution, or areas of the
world where it lives.
Niche generalist- species that live under a wide
range of conditions.
Niche specialist- species that live only in specific
habitats.
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The Fossil Record
Fossils- remains of
organisms that have been
preserved in rock. Much of
what we know about
evolution comes from the
fossil record.
The average life span of a
species appears to be only
about 1 million years.
Extinctions may occur
because:
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No favorable
environment to move to.
Favorable environment
may already be
occupied.
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The Five Global Mass Extinctions
Mass extinction- when large numbers of species
went extinct over a relatively short period of time.
Better known
extinction
happened during the cretaceous
period wiping out 50% of all
species including the dinosaurs.
Consensus among scientists says
it was a meteorite that hit Earth,
formed a giant dust ball that
blocked out the sun for many
years.
Greatest on record
~90% of marine and
70% terrestrial
vertebrates went
extinct. 250 million
years ago.
The Sixth Mass Extinction
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Scientists feel that we are in our sixth
mass extinction, occurring in the last two
decades.
Estimates of extinction rates vary widely,
from 2 % to 25% by 2020.
In contrast to previous mass extinctions,
scientists agree that this one is caused by
humans.