Transcript Chapter 05_lecture

Chapter 5
Evolution of Biodiversity
Earth is home to a tremendous
diversity of species
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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.
Species – can interbreed and produce
viable offspring
Biodiversity – most commonly
measured by the number of species in
any give place
CURRENTLY: Scientists have named 2
million species
Insect group – most diverse!
Insect species – 30 million
Total Estimate – between 5 and 100
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.
Species richness or eveness often
declines after a human disturbance.
Knowing the species richness and
eveness of an ecosystem seves as a
baseline for change.
Pg. 124 Do the Math
Phylogenies – branching patterns of evolutionary
relationships used to organize species.
Traits used to organize species: morphology; behavior,
and genetic similarity.
Why is it challenging to determine the
number of species on Earth?
Why are estimates of species diversity
valuable to environmental scientists?
What is the difference between species
richness and species evenness?
Why are they both important?
Evolution is the mechanism
underlying biodiversity
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Evolution- a change in the genetic
composition of a population over time.
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Microevolution- evolution below the
species level. (varieties of apples etc)
Macroevolution- Evolution which gives
rise to new species or new genera,
family, class or phyla.
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Speciation – evolution of new species
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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.
Two processes that create genetic diversity:
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Mutation- a random change in the
genetic code.
Recombination – when chromosomes are
duplicated during reproductive cell
division and a piece of one chromosome
breaks off and attaches to another.
Genotypes vs Phenotypes
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Phenotype- the actual set of traits
expressed in an individual. (color of eyes)
• Genotype – blueprint for complete set of
traits (genes that code for eye color).
• Changes in the genotype due to
mutation can cause changes in
phenotype.
• Most phenotypes are determined by
both environment and genotype.
• Turtle/crocodile eggs…
• Water flea shape
• By being able to respond to changing
conditions, organisms can improve their
ability to survive and reproduce.
Dusky-headed conure parrots
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.
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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.
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Evolution by Random Processes
Mutation- occur randomly and can add to the
genetic variation of a population. (Fig. 5.12a)
Genetic drift- change in the genetic composition
of a population over time as a result of random
mating. (Fig. 5.12b)
Bottleneck effect- a reduction in the genetic
diversity of a population caused by a reduction
in its size. (cheetah)
Founder effect- a change in a population
descended from a small number of colonizing
individuals. (island)
Let’s Review…
• What is evolution, and what are the 3
main ways in which it occurs?
• How are artificial and natural selection
similar? How are they different?
• How does evolution lead to biodiversity?
How do we go from
Microevolution to
Macroevolution?
Speciation and extinction
determine biodiversity
• Allopatric speciation- when new species are
created by geographic or reproductive
isolation.
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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.
Naturally or through human action (breeders – crops,
strawberries, bananas etc)
Polypolid cannot interbreed with diploid ancestors – naturally
isoated.
The pace of evolution
Can take hundreds to millions of years
Average is one new species every 3
million years.
Fig. 5.16 – RAPID - cichlid fishes
The pace of evolution
FIG 5.17
Four factors for successful adaptation:
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Rate of environmental change (acidic lakes)
2. Genetic variation
(high variation = more chance of new species)
3. Population size
(smaller = more likely to have new species)
4. Generation time
(shorter generation time = more likely evolve)
The pace of evolution
Evolution occurs more rapidly in
populations of GMOs.
• Bacillus thuringiensis – produces
insecticide
• Bt – corn, Bt-cotton
Review
• How does geographic isolation lead to
reproductive isolation?
• What factors influence a species
chances of adapting successfully to a
change in the environment?
• Why is the pace of human-driven
evolution faster than that of natural
evolutionary processes?
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.
• Biotic factors can limit a niche as
well:
• Competition
• Predation
• Disease
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.
Generalist
Specialist
Spittlebug
Leaf Beetle
Environmental Change and Species
Distribution
• Evidence:
• Lake sediment/pollen
• Fig. 5.20 – red pine vs loblolly pine
Environmental Change and Species
Extinctions
• Avg. lifespan of a species – 1-10mill years.
• 99% of species that once lived – EXTINCT!
Why do species go extinct?
• No favorable environment
• Polar bears
• May be occupied (Fig. 5.21)
• Too rapid of a change
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 Five Global Mass Extinctions
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Mass extinction- when large numbers of species went
extinct over a relatively short period of time.
251 mya – largest on record
65 mya - dinosaurs
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.
Review
• How do fundamental niches and
realized niches differ?
• How does environmental change
determine species distribution?
• When does environmental change
lead to extinction?
• How are human activities affecting
extinction rates?
• Why is human impact a concern at
all? (why should we care?)