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17.3 – The Process of Speciation Chapter 17 – Evolution of Populations 17.3 The Process of Speciation 17.3 – The Process of Speciation THINK ABOUT IT How does one species become two? Thoughts? 17.3 – The Process of Speciation Isolating Mechanisms Species: A population or group of populations whose members can interbreed and produce fertile offspring Speciation - is the formation of a new species. A species is a population whose members can interbreed and produce fertile offspring. When individuals from a population stop interbreeding, reproductive isolation has occurred. 17.3 – The Process of Speciation Reproductive Isolation 17.3 – The Process of Speciation Reproductive Isolating Mechanisms • What types of isolation lead to the formation of new species? 1. Behavioral Isolation 2. Geographic Isolation 3. Temporal isolation 17.3 – The Process of Speciation Behavioral Isolation 1. Behavioral Isolation - Occurs when two populations that are capable of interbreeding develop differences in courtship rituals or other behaviors. Example: these are similar birds whose habitats overlap, but they will not mate because they use different songs to attract mates! 17.3 – The Process of Speciation Behavioral Isolation Species that are behaviorally isolated are likely to have complex mating behaviors, such as elaborate mating rituals 17.3 – The Process of Speciation Geographic isolation 2. Geographic Isolation - Occurs when two populations are separated by geographic barriers Examples = Rivers, Mountains, Canyons, and bodies of water. 17.3 – The Process of Speciation Geographic Isolation 17.3 – The Process of Speciation Temporal isolation Temporal isolation - occurs when two or more species reproduce at different times. 17.3 – The Process of Speciation Speciation in Darwin’s Finches • Question: How might the founder effect and natural selection have produced reproductive isolation that led to the speciation of Galapagos finches? Answer: Speciation in Galapagos finches happened by: founding of a new population, geographic isolation, changes in the new population’s gene pool, behavioral isolation, and ecological competition. 17.3 – The Process of Speciation 1. Founders Arrive • A long time ago, a few finches from SOUTH AMERICA arrived on one of the Galapagos islands. • Why? (May have been blown off course by a storm) • FOUNDER EFFECT: Allele frequencies of this new founding finch population was different from allele frequencies in the original South American population. 17.3 – The Process of Speciation 2. Geographic Isolation • Island environment was different than South America • Combination of founder effect, geographic isolation & natural selection enabled the island finches to evolve into a NEW SPECIES-Species A • Then, a few birds from species A moved to another island. • The 2 finch populations on the two islands were now geographically isolated and no longer shared a common gene pool! 17.3 – The Process of Speciation 3. Changes in Gene Pools • Over time, populations on each island ADAPTED to local environments • How? Ex. Beak size and seed size, directional selection • Over time, natural selection would have caused that population to evolve larger beaks, forming a distinct population, B, with a new phenotype. 17.3 – The Process of Speciation 4. Behavioral Isolation • If a few birds from the second island return back to the first island, will population A reproduce with population B? • Probably not! Different courtship and mate preferences • So, differences in beak size, combined with mating behavior, can lead to reproductive isolation • Populations are now 2 distinct species! 17.3 – The Process of Speciation 5. Competition & Continued Evolution • As these two new species live together on the first island, they compete for seeds • More specialized birds have less competition for certain seeds & food! • Overtime, species evolve in a way that increases differences between them! Species B can evolve into a new Species- C 17.3 – The Process of Speciation Speciation in Darwin’s Finches • The combined processes of geographic isolation on different islands, genetic change, and behavioral isolation repeated itself over and over across the Galapagos islands • Over many generations, the process could have produced the 13 different finch species found there today! 17.3 – The Process of Speciation Review Questions • Why did selection increase genetic variation among finches on different islands? • How did selection lead to speciation? • Why did geographic isolation have to occur before changes happened in the two gene pools?