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 speciation- explain

Apply Concepts Explain how the vegetarian tree finch. Which feeds on fruit might have evolved

CH 17 EVOLUTION OF POPULATIONS17.3 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. Part of population breaks off and becomes separated

2. Barrier prevents two groups from coming in contact with each other

3. Groups adapt separately to their own environments

4. 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.