Chapter 17: Evolution of Populations
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Transcript of Chapter 17: Evolution of Populations
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Chapter 17:Evolution of PopulationsSection 17-3: The Process of Speciation
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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
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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
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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
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Testing Natural Selection in Nature•The Grants measured and recorded beak
lengths•Documented directional selection as
environmental conditions changed
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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
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Founders Arrive• Few finches from South
America arrived in Galapagos
• Founder effect
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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
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Changes in Gene Pools• Populations on each island
adapt to local environments
• Distinct populations form with distinct phenotypes
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Behavioral Isolation• If you bring populations
back together, they will probably not breed
• Mating preference
• Now have reproductive isolation – two distinct species
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Competition and Continued Evolution• Competition requires
finches to develop different adaptations, different levels of fitness
• More specialized birds have less competition
• New species develop