1. Copyright © 2005 Pearson Prentice Hall, Inc. Ch.16 The Origin of Species What Is a Species? How Do New Species Form? –allopatric and sympatric speciation How Is Reproductive Isolation Between Species Maintained? What Causes Extinction?

2. Copyright © 2005 Pearson Prentice Hall, Inc.

3. What Is a Species? Biologists Need a Clear Definition of Species Species Are Groups of Interbreeding Populations Appearance Can Be Misleading –Members of a species may differ in appearance (F16.1 p. 303)

4. Copyright © 2005 Pearson Prentice Hall, Inc.

5. How Do New Species Form? Models of allopatric and sympatric speciation (F16.2 p. 304) Allopatric Speciation (F16.3 p. 305) –By Geographic Separation of a Population Sympatric Speciation (F16.4 p. 305) –By Ecological Isolation of a Population

6. Copyright © 2005 Pearson Prentice Hall, Inc. reproductive isolation genetic divergence geographical isolation ecological isolation AllopatricSympatric original population

7. Copyright © 2005 Pearson Prentice Hall, Inc.

10. How Do New Species Form? Changes in Chromosome Number Can Lead to Sympatric Speciation –Speciation by polyploidy (F16.5 p. 306)

11. Copyright © 2005 Pearson Prentice Hall, Inc. fertilization meiosis meiosis fails; no viable gametes viable, diploid gametes Case 1: Self- fertilization Case 2: Breeds with normal diploid parent meiosis

12. Copyright © 2005 Pearson Prentice Hall, Inc. How Do New Species Form? Change Over Time Within a Species Can Cause Apparent “Speciation” in the Fossil Record –Interpreting an evolutionary tree (F16.6 p. 307)

13. Copyright © 2005 Pearson Prentice Hall, Inc. present change in form past time Copyright © 2005 Pearson Prentice Hall, Inc.

14. How Do New Species Form? Under Some Conditions, Many New Species May Arise –Adaptive radiation (F16.7 p. 308 )

15. Copyright © 2005 Pearson Prentice Hall, Inc.

17. Maintaining Reproductive Isolation Between Species (T16.1,p. 310) Premating Isolating Mechanisms Prevent Mating Between Species –Members of Different Species May Be Prevented from Meeting –Different Species May Occupy Different Habitats Ecological isolation (F16.8 p. 309) –Different Species May Breed at Different Times Temporal isolation (F16.9 p. 309) –Different Species May Have Different Courtship Rituals –Species’ Differing Sexual Organs May Foil Mating Attempts

18. Copyright © 2005 Pearson Prentice Hall, Inc.

20. Maintaining Reproductive Isolation Between Species (T16.1,p. 310) Postmating Isolating Mechanisms Limit Hybrid Offspring –One Species’ Sperm May Fail To Fertilize Another Species’ Eggs –Hybrid Offspring May Survive Poorly –Hybrid Offspring May Be Infertile Mechanisms of Reproductive Isolation

21. Copyright © 2005 Pearson Prentice Hall, Inc.

22. What Causes Extinction? Localized Distribution & Overspecialization Make Species Vulnerable in Changing Environments –Very localized distribution can endanger a species (F16.10 p. 311) –Extreme specialization places species at risk (F16.11 p. 311) –Ethiopian wolves (FE16.1 p. 312) –Interactions with Other Organisms May Drive a Species to Extinction –Habitat Change and Destruction Are the Leading Causes of Extinction

23. Copyright © 2005 Pearson Prentice Hall, Inc.