1. What is a Species? There is only one extant (existing) human species.

2. What is a Species? And these are all members of a single species.

3. Concept 24.1: The biological species concept emphasizes reproductive isolation Biological Species Concept (one way to divide species): –A species is a group of populations whose members can breed and produce viable, fertile offspring –Ability to mate = formation of a species © 2011 Pearson Education, Inc.

4. It’s all about ability to breed (a) Similarity between different species (b) Diversity within a species

5. How Do Species Arise? The key to speciation is isolation. Two ways isolation can occur Geographic isolation Reproductive isolation

6. Process of speciation: Parent species I. Barrier 2 separate species III. Don’t interbreed II. Diverge

7. Allopatric (“Other Country”) Speciation In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations –For example, the flightless cormorant of the Galápagos likely originated from a flying species on the mainland © 2011 Pearson Education, Inc.

8. The Process of Allopatric Speciation The definition of barrier depends on the ability of a population to disperse –For example, a canyon may create a barrier for small rodents, but not birds, coyotes, or pollen © 2011 Pearson Education, Inc. A. harrisiiA. leucurus

9. Allopatric Speciation Two species of ground squirrel are postulated to have descended from a common ancestral population that was separated by formation of the Grand Canyon. Harris’ antelope squirrel White-tailed antelope squirrel

10. Once isolated: Separate populations may evolve independently through mutation, natural selection, and genetic drift © 2011 Pearson Education, Inc.

11. Reproductive Isolation is the driving force behind Speciation A new species will form when reproductive isolation occurs –Absence of gene flow Reproductive Isolation: –The existence of biological factors (barriers) that prevent two individuals of a species from mating and producing viable and fertile offspring Hybrids: –Offspring of crosses between two different species Barriers may contribute to reproductive isolation before or after fertilization (pre- or postzygotic barriers) © 2011 Pearson Education, Inc.

12. Prezygotic barriers block fertilization from occurring by: –Impeding different species from attempting to mate –Preventing the successful completion of mating –Hindering fertilization if mating is successful –5 types of prezygotic barriers © 2011 Pearson Education, Inc.

13. Figure 24.3_b Prezygotic barriers Habitat Isolation Temporal Isolation Behavioral Isolation Mechanical Isolation Gametic Isolation Individuals of different species MATING ATTEMPT FERTILIZATION (a) (c) (e) (f) (b) (g) (d)

14. Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation (

15. Courtship rituals, like these, are critical for mating within a species, but ineffective for attracting members of other species. Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation

17. Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult: –Reduced hybrid viability –Reduced hybrid fertility © 2011 Pearson Education, Inc.

18. Reduced Hybrid Viability Reduced Hybrid Fertility Hybrid Breakdown FERTILIZATION VIABLE, FERTILE OFFSPRING Postzygotic barriers (k) (h) (i) (j) (l) Figure 24.3_c

19. Concept 24.2: Speciation can take place with or without geographic separation Speciation can occur in two ways: –Allopatric speciation –Sympatric speciation © 2011 Pearson Education, Inc.

20. Figure 24.5 (a) (b) Allopatric speciation. A population forms a new species while geographically isolated from its parent population. Sympatric speciation. A subset of a population forms a new species without geographic separation.

21. Sympatric (“Same Country”) Speciation In sympatric speciation, speciation takes place in geographically overlapping populations How can this occur if parent species is in same area? Provide an example. © 2011 Pearson Education, Inc.

22. Sympatric (“Same Country”) Speciation In sympatric speciation, speciation takes place in geographically overlapping populations In a sympatric speciation, various factors can limit gene flow: –Habitat differentiation –Sexual selection © 2011 Pearson Education, Inc.

23. Allopatric and Sympatric Speciation: A Review In allopatric speciation, geographic isolation restricts gene flow between populations Reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations –Even if contact is restored between populations, interbreeding is prevented © 2011 Pearson Education, Inc.

24. In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species –Sympatric speciation can result from polyploidy, natural selection, or sexual selection © 2011 Pearson Education, Inc.