1. End Show Slide 1 of 33 Copyright Pearson Prentice Hall 16-3 The Process of Speciation 17-3 The Process of Speciation

2. End Show 16-3 The Process of Speciation Slide 2 of 33 Copyright Pearson Prentice Hall 16-3 The Process of Speciation Natural selection and genetic drift can change the relative frequencies of alleles in a population and lead to speciation. Speciation is the formation of new species. A species is a group of organisms whose members can interbreed with one another and produce fertile offspring. This means that the members of a species share a common gene pool. A genetic change in one individual can spread through the population if it increases fitness.

3. End Show 16-3 The Process of Speciation Slide 3 of 33 Copyright Pearson Prentice Hall Isolating Mechanisms What types of isolation lead to the formation of new species? The gene pools of two populations must become separated for them to become new species.

4. End Show 16-3 The Process of Speciation Slide 4 of 33 Copyright Pearson Prentice Hall Isolating Mechanisms When populations become reproductively isolated, they can evolve into 2 separate species. When the members of two populations cannot interbreed and produce fertile offspring, reproductive isolation has occurred. The populations then have 2 separate gene pools.

5. End Show 16-3 The Process of Speciation Slide 5 of 33 Copyright Pearson Prentice Hall Isolating Mechanisms Reproductive isolation can develop in a variety of ways, including: behavioral isolation geographic isolation temporal isolation

6. End Show 16-3 The Process of Speciation Slide 6 of 33 Copyright Pearson Prentice Hall Isolating Mechanisms Behavioral Isolation Behavioral isolation occurs when two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior. For example, 2 populations of meadowlarks, known as eastern and western meadowlarks, can but do not mate with one another primarily because they use different songs to attract mates.

7. End Show 16-3 The Process of Speciation Slide 7 of 33 Copyright Pearson Prentice Hall Isolating Mechanisms Geographic Isolation Geographic isolation occurs when two populations are separated by geographic barriers such as rivers or mountains. An example of this occurred about 10,000 years ago when the formation of the Grand Canyon split up a population of squirrels.

8. End Show 16-3 The Process of Speciation Slide 8 of 33 Copyright Pearson Prentice Hall The Kaibab squirrel (black) on the north rim evolved separately from the Abert squirrel (grey) on the south rim.

9. End Show 16-3 The Process of Speciation Slide 9 of 33 Copyright Pearson Prentice Hall Isolating Mechanisms Temporal Isolation Temporal isolation occurs when two or more species reproduce at different times. There are 3 different species of orchid, for example, that live in the same rain forest. Each species releases pollen in one day but, since the pollen is released on 3 different one day periods, they cannot pollinate one another.

10. End Show 16-3 The Process of Speciation Slide 10 of 33 Copyright Pearson Prentice Hall Testing Natural Selection in Nature Studies showing natural selection in action involve descendants of the finches that Darwin observed in the Galápagos Islands. The finches Darwin saw were different, but he hypothesized that they had descended from a common ancestor. He proposed that natural selection shaped the beaks of different bird populations as they became adapted to eat different foods.

11. End Show 16-3 The Process of Speciation Slide 11 of 33 Copyright Pearson Prentice Hall Testing Natural Selection in Nature

12. End Show 16-3 The Process of Speciation Slide 12 of 33 Copyright Pearson Prentice Hall Testing Natural Selection in Nature

13. End Show 16-3 The Process of Speciation Slide 13 of 33 Copyright Pearson Prentice Hall Testing Natural Selection in Nature Peter and Rosemary Grant tested Darwin’s hypothesis, which relied on two testable assumptions: For beak size and shape to evolve, there must be enough heritable variation in those traits to provide raw material for natural selection. Differences in beak size and shape must produce differences in fitness, causing natural selection to occur.

14. End Show 16-3 The Process of Speciation Slide 14 of 33 Copyright Pearson Prentice Hall Testing Natural Selection in Nature The Grants tested these hypotheses on the medium ground finch on Daphne Major, one of the Galápagos Islands. During the rainy season, there is plenty of food. During droughts, food becomes scarce. Individual birds with different-sized beaks had different chances of survival during a drought.

15. End Show 16-3 The Process of Speciation Slide 15 of 33 Copyright Pearson Prentice Hall Testing Natural Selection in Nature When food was scarce, individuals with large beaks were more likely to survive.

16. End Show 16-3 The Process of Speciation Slide 16 of 33 Copyright Pearson Prentice Hall Testing Natural Selection in Nature This was evidence of the process of evolution. The Grants could then conclude that beak size can be changed by natural selection. They documented the directional nature of the selection. Their data showed competition & climate drive natural selection. Their work also suggested that natural selection can lead to speciation.

17. End Show 16-3 The Process of Speciation Slide 17 of 33 Copyright Pearson Prentice Hall Speciation in Darwin's Finches Speciation in the Galápagos finches occurred by: founding of a new population geographic isolation changes in new population's gene pool behavioral isolation ecological competition

18. End Show 16-3 The Process of Speciation Slide 18 of 33 Copyright Pearson Prentice Hall Speciation in Darwin's Finches Founders Arrive A few finches—species A— travel from South America to one of the Galápagos Islands. Because of the founder effect, the allele frequencies of this founding finch population could have already differed from those in the South American population. Species A survive and reproduce.

19. End Show 16-3 The Process of Speciation Slide 19 of 33 Copyright Pearson Prentice Hall Speciation in Darwin's Finches Geographic Isolation Some birds from species A cross to a second island. The two populations no longer share a gene pool.

20. End Show 16-3 The Process of Speciation Slide 20 of 33 Copyright Pearson Prentice Hall Speciation in Darwin's Finches Changes in the Gene Pool Seed sizes on the second island favor birds with large beaks. The population on the second island evolves into population B, with larger beaks.

21. End Show 16-3 The Process of Speciation Slide 21 of 33 Copyright Pearson Prentice Hall Speciation in Darwin's Finches Behavioral Isolation If population B birds cross back to the first island, they will not mate with birds from population A. Sexual selection would occur – species B birds would look for mates that had a large beak like their own. Differences in other mating behavior might also work to keep their gene pools separate. Populations A and B would now be 2 separate species.

22. End Show 16-3 The Process of Speciation Slide 22 of 33 Copyright Pearson Prentice Hall Speciation in Darwin's Finches Ecological Competition As species A and B compete for available seeds on the first island, they continue to evolve in a way that increases the differences between them. This would insure less competition.

23. End Show 16-3 The Process of Speciation Slide 23 of 33 Copyright Pearson Prentice Hall Speciation in Darwin's Finches Continued Evolution This process of isolation, genetic change, and reproductive isolation probably repeated itself often across the entire Galápagos island chain. In the end, it produced the 13 species of finches we see today.