1. Chapter 17: Evolution of Populations Section 17-3: The Process of Speciation

2. Isolating Mechanisms Natural selection and genetic drift alone to not create new species Speciation is the formation of new species Reproductive isolation occurs when a population splits into 2 groups, and the two populations can no longer interbreed Different species

4. Isolating Mechanisms Behavioral isolation occurs when two populations that are capable of interbreeding develop differences in courtship rituals or other behaviors Geographic isolation occurs when two populations are separated by geographic barriers Temporal isolation occurs when two or more species reproduce at different times

5. Testing Natural Selection in Nature Darwin proposed that Galapagos finches descended from common ancestor, with natural selection shaping beaks as they adapted to different food sources

6. Testing Natural Selection in Nature The Grants measured and recorded beak lengths Documented directional selection as environmental conditions changed

7. Speciation in Darwin’s Finches How founder effect and natural selection lead to reproductive isolation Current hypothesis is speciation in Darwin’s finches occurred by founding of new population geographic isolation, changes in the new population’s gene pool, behavioral isolation, and ecological competition

8. Founders Arrive Few finches from South America arrived in Galapagos Founder effect

9. Geographic Isolation Island environment different from mainland Island finch population evolved into new species Some crossed to new island Usually don’t fly over water

10. Changes in Gene Pools Populations on each island adapt to local environments Distinct populations form with distinct phenotypes

11. Behavioral Isolation If you bring populations back together, they will probably not breed Mating preference Now have reproductive isolation – two distinct species

12. Competition and Continued Evolution Competition requires finches to develop different adaptations, different levels of fitness More specialized birds have less competition New species develop