Ecological Niches and Adaptation

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Transcript Ecological Niches and Adaptation

Isolation Leading to Speciation…
Speciation - formation of two species
from one species because of
divergent natural selection
Difference between Geographic
and Reproductive Isolation
Geographic
• Physically separated for long
periods of time
• Physical barrier
• Volcano/earthquake
• Wind/water
Reproductive
• Mutation and natural
selection
• Divergent evolution
• Change enough to not be
able to interbreed
Can take hundreds of years… if the species is quickly
reproducing. Otherwise, it takes tens of thousands to
millions of years!
Geographic Isolation
…can lead to reproductive isolation, divergence
of gene pools and speciation.
Convergent evolution
• Organisms have similar
adaptations to similar
environments, e.g.
whales and sharks, bats
and birds
These two succulent plant genera,
Euphorbia and Astrophytum, are only
distantly related, but have independently
converged on a very similar body form.
Convergent evolution
Convergent evolution
Divergent Evolution
• Organisms are related but have different
adaptations to different environments
Divergent Evolution
Or Adaptive Radiation
Darwin’s Finches
Divergent
Convergent
Coevolution
• Refers to complex
interactions that involve
evolutionary
adaptations between 2
species
• E.g. Acacia tree and
leafcutter ants,
flowering plants and
their pollinators
Evolution and Adaptation
• Co-Evolution
– Populations of two different species
interacting over a long period of time
– Changes in the gene pool of of one
species changes the gene pool of another
species
• Predator-Prey Relationships
• Plant defense mechanisms
Extinction: Lights Out
• Extinction occurs
when the
population
cannot adapt to
changing
environmental
conditions.
The
golden toad of Costa Rica’s
Monteverde cloud forest has
become extinct because of
changes in climate.
Figure 4-11
Extinction: Lights Out
• 99.9 % of all
species that
ever existed
are now
extinct
Figure 4-11
Cenozoic
Era
Period
Millions of
years ago
Quaternary
Today
Tertiary
65
Mesozoic
Cretaceous
Jurassic
180
Triassic
Species and families
experiencing
mass extinction
Extinction Current extinction crisis caused
by human activities. Many species
are expected to become extinct
Extinction within the next 50–100 years.
Cretaceous: up to 80% of ruling
reptiles (dinosaurs); many marine
species including many
foraminiferans and mollusks.
Extinction
Triassic: 35% of animal families,
including many reptiles and marine
mollusks.
Bar width represents relative
number of living species
250
Extinction
345
Extinction
Permian
Paleozoic
Carboniferous
Devonian
Permian: 90% of animal families,
including over 95% of marine
species; many trees, amphibians,
most bryozoans and brachiopods,
all trilobites.
Devonian: 30% of animal
families, including agnathan and
placoderm fishes and many
trilobites.
Silurian
Ordovician
Cambrian
500
Extinction
Ordovician: 50% of animal
families, including many
trilobites.
Fig. 4-12, p. 93
Extinction
• Background extinction
– Normal extinction of various
species as a result of changes in
local environmental conditions
• Mass extinction
– extinction resulting from
catastrophic, wide-spread event in
which large groups of existing
species are wiped out
Period of Recovery Following
Extinction
Adaptive radiation Process in which numerous new
species evolve to fill vacant and
new ecological niches in changed
environments