1 Review What is geographic isolation
Predict A newly formed lake divides a population of
beetle species into two groups. What other factors
besides isolation might lead to the two groups
becoming separate species
2 Review What types of reproductive isolation may
have been important in Galapagos finch speciationexplain
Apply Concepts Explain how the vegetarian tree
finch. Which feeds on fruit might have evolved
CH 17 EVOLUTION OF POPULATIONS
17.3 The Process of Speciation

How does one species become two?
Speciation

Formation of a new species
 Species-
group of organisms that are similar enough to
mate and to produce fertile offspring.
Speciation Steps
1.
2.
3.
4.
Part of population breaks off and becomes
separated
Barrier prevents two groups from coming in
contact with each other
Groups adapt separately to their own
environments
Adaptations occur and add up until the two
groups become different enough where even
if barrier is removed the groups do not
interbreed.
Lion and Tiger
Polar Bear and Grizzly Bear
Reproductive Isolation

Inability of one group to mate successfully with any
other group.
Behavioral Isolation

Two populations that are capable of interbreeding
develop differences in courtship rituals or other
behaviors.
Geographic Isolation

Two populations are separated by geographic
barriers such as rivers, mountains, or bodies of
water.
Temporal Isolation

Two or more species reproduce at different times.
Speciation in Darwin’s Finches





Founding of a new population
Geographic isolation
Changes in the new population’s gene pool
Behavioral isolation
Ecological competition.
Founders Arrive

Many years ago a few
finches (species M)
arrived from South
America.
Geographic Isolation



The island had a unique
environment
Founder effect,
geographic isolation,
and natural selection
resulted in a new
species
Species A.
Changes in Gene Pools


Populations on each
island adapted to local
environments
Two distinct populations
evolved A and B.
Behavioral Isolation



Some species B finches
go back to first island
Enough time has passed
where the two species
remain isolated
Sexual selection keep
them from mating.
Competition and Continued Evolution


Species evolve in a way
that increases the
differences between
them, and new species
may evolve C, D, and E
More specialized birds
have less competition
for food.