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Speciation Speciation: The formation of a new species. The gene pool can split when an interbreeding population divides into groups that no longer breed with one another. Isolating Mechanisms: Because these populations no longer interbreed, they have undergone reproductive isolation. Groups with isolated gene pools can evolve into separate species. 1. Behavioral Isolation: Differing behaviors prevent interbreeding. Example: Eastern and Western Meadowlarks have developed different mating behaviors and do not respond to each other’s courtship songs. 2. Temporal Isolation: Species reproduce at different times. Example: Three similar rainforest orchids bloom on different days. Since their blooms only last one day, the orchids are unable to cross pollinate with each other. 3. Geographic Isolation: Geographic barriers separate two populations. Example: Abert’s and Kaibab squirrels live on different sides of the Grand Canyon’s Colorado River. Ex. Finch Speciation A combination of these isolating mechanisms provides possible explanations for Galapagos Island Finch speciation. Large cactus finch Gray warbler finch How might the founder effect have contributed to genetic variation in finch populations on different islands? Why did selection increase genetic variation among finches on different islands? How did selection lead to speciation? Divergent Evolution 1. When two populations from the same species become increasingly distinct. Two separate species arise. 2. Gives rise to homologous structures Convergent Evolution 1. When different species evolve similar characteristics because of similar environments (ecological niches). 2. Gives rise to analogous structures. Speed of Speciation How fast or slow does the process occur? Two ideas 1. Gradualism – Change happens slowly over time and is constant 2. Punctuated Equilibrium – Massive changes take place after dramatic change in the environment (earthquakes, volcanoes etc.) Remember……