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Speciation
Speciation: The formation of a
new species.
The gene pool can split when
an interbreeding population
divides into groups that no
longer breed with one
another.
Isolating Mechanisms:
Because these populations no
longer interbreed, they have
undergone reproductive isolation.
Groups with isolated gene pools can
evolve into separate species.
1. Behavioral Isolation: Differing
behaviors prevent interbreeding.
Example: Eastern and Western
Meadowlarks have developed
different mating behaviors and
do not respond to each other’s
courtship songs.
2. Temporal Isolation: Species reproduce
at different times.
Example: Three similar rainforest orchids bloom on
different days. Since their blooms only last one day, the
orchids are unable to cross pollinate with each other.
3. Geographic Isolation: Geographic
barriers separate two populations.
Example: Abert’s and Kaibab squirrels live on different
sides of the Grand Canyon’s Colorado River.
Ex. Finch Speciation
A combination of these isolating
mechanisms provides possible
explanations for Galapagos Island
Finch speciation.
Large cactus finch
Gray warbler finch
How might the founder effect have
contributed to genetic variation in finch
populations on different islands?
Why did selection increase genetic
variation among finches on different
islands?
How did selection lead to speciation?
Divergent Evolution
1.
When two populations from the same species become
increasingly distinct. Two separate species arise.
2.
Gives rise to homologous structures
Convergent Evolution
1. When different species evolve similar characteristics because
of similar environments (ecological niches).
2. Gives rise to analogous structures.
Speed of Speciation
How fast or slow does the
process occur?
Two ideas
1.
Gradualism – Change
happens slowly over time
and is constant
2.
Punctuated Equilibrium –
Massive changes take place
after dramatic change in the
environment (earthquakes,
volcanoes etc.)
Remember……