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Chapter 14

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Chapter 14

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  1. Chapter 14 0 The Origin of Species

  2. Origin of Species • Discuss this with a neighbor now. • If microevolution were all that occurred, then the Earth would inhabited by a highly adapted version of the first form of life. • How could the diversity of organisms that we see today occur? • Darwin’s theory focused on the gradual adaptation of populations to their environment. • This is called microevolution.

  3. Figure 14.1 • 14.1 The origin of species is the source of biological diversity • Speciation, the origin of new species • Is at the focal point of evolution

  4. 14.8 Adaptive radiation may occur in new or newly vacated habitats • In adaptive radiation, the evolution of new species • Occurs when mass extinctions or colonization provide organisms with new environments • Think back to the hummingbird video

  5. Cactus-seed-eater (cactus finch) Tool-using insect-eater (woodpecker finch) Seed-eater (medium ground finch) • Island chains • Provide examples of adaptive radiation Figure 14.8A

  6. 2 B 1 A B B 3 C C 4 C C B D D C 5 D Figure 14.8B

  7. CONCEPTS OF SPECIES • 14.2 What is a species? • Carolus Linnaeus, a Swedish physician and botanist • Used physical characteristics to distinguish species • Developed the binomial system of naming organisms • Linnaeus’ system established the basis for taxonomy • The branch of biology concerned with naming and classifying the diverse forms of life

  8. Similarities between some species and variation within a species • Can make defining species difficult Figure 14.2A Figure 14.2B

  9. The Biological Species Concept • The biological species concept defines a species as • A population or group of populations whose members have the potential to interbreed and produce fertile offspring

  10. 14.3 Reproductive barriers keep species separate • Reproductive barriers • Serve to isolate a species’ gene pool and prevent interbreeding • Are categorized as prezygotic or postzygotic • What is a zygote? • What do we mean by prezygotic and postzygotic barriers?

  11. Prezygotic Barriers • Prevent mating or fertilization between species • Essentially, these barriers prevent organisms from having sex – thus making fertilization an impossibility

  12. Figure 14.3A • In temporal isolation • Two species breed at different times • Different seasons, times of day, or years • Ex. Eastern and Western spotted skunk • Their territories overlap • Western breeds in fall • Eastern breeds in winter • Plants do this as well • Seed production varies

  13. In habitat isolation • Populations live in the same general area but do not meet • In some cases, it depends on the organisms ability to move about (fly, swim, walk) • Ex. Antelope squirrels of the Grand Canyon are separated by the Colorado River • Isolation does not necessarily lead to new species, but creates opportunities for new ones to emerge

  14. Figure 14.3B • In behavioral isolation • There is little or no sexual attraction between species, due to specific behaviors Ex. Courtship Rituals, Birdsongs, firefly flash

  15. Figure 14.3C • In mechanical isolation • Female and male sex organs or gametes are not compatible Ex. Hummingbird beaks and flower pollination Ex. Copulatory organs of insects

  16. In gametic isolation • Female and male may copulate but the gametes do not unite to form a zygote Ex. Can operate even if fertilization is external. Fish sperm are released into the water but only females the same can take them up. Ex. With internal fertilization, gametes cannot survive in the reproductive tract of another species

  17. Postzygotic Barriers • Operate after hybrid zygotes are formed • Organisms may have been capable of having sex, but there are issues with the zygote • Three types: • Hybrid inviability • Individuals do not survive or are frail • Hybrid breakdown • First generation of hybrids are fertile but the result of two hybrids breeding are not • Hybrid sterility (next page)

  18. Figure 14.3D • One postzygotic barrier is hybrid sterility • Where hybrid offspring between two species are sterile and therefore cannot mate

  19. E RECENT Equus Hippidion and other genera PLEISTOCEN Nannippus Pliohippus Neohipparion Hipparion PLIOCENE Megahippus Sinohippus Callippus Archaeohippus MIOCENE Merychippus Hypohippus Anchitherium Parahippus Miohippus OLIGOCENE Mesohippus Paleotherium Epihippus Propalaeotherium Orohippus Pachynolophus EOCENE Grazers Browsers Hyracotherium • 14.13 Evolutionary trends do not mean that evolution is goal directed • Evolutionary trends reflect species selection • The unequal speciation or unequal survival of species on a branching evolutionary tree Figure 14.13