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Chapter 17: Evolution of Populations

Chapter 17: Evolution of Populations. Section 17-3: The Process of Speciation. Isolating Mechanisms. Natural selection and genetic drift alone to not create new species Speciation is the formation of new species

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Chapter 17: Evolution of Populations

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  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

  3. 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

  4. 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

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

  6. 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

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

  8. 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

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

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

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

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