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Why are there different species in different parts of the world? Why do some areas have higher biodiversity than others?

Explaining biodiversity. Why are there different species in different parts of the world? Why do some areas have higher biodiversity than others?. Biogeography geographic patterns of species diversity and distribution contributes to global biodiversity

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Why are there different species in different parts of the world? Why do some areas have higher biodiversity than others?

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  1. Explaining biodiversity Why are there different species in different parts of the world? Why do some areas have higher biodiversity than others? • Biogeography • geographic patterns of species diversity and distribution • contributes to global biodiversity • reflects patterns of evolution, dispersal, and extinction

  2. ostrich Africa rhea S. Amer. emu Austral. Biogeography reflects past dispersal and isolation Continental drift When did ratites (ostriches, emus, rheas) originate? time Where and when did marsupials originate?

  3. Biogeography reflects past dispersal and isolation • Island biogeography • explaining patterns of diversity on islands • effects of isolation and area • applies to other isolated habitats

  4. Islands aren’t the only isolated habitats lakes and ponds mountaintops fragmented habitats

  5. Effect of habitat isolation Lesser Antilles • isolated (distant) islands contain fewer • species than nearby islands

  6. Effect of habitat area • larger islands contain more • species than smaller islands

  7. Species richness depends on area and isolation bird

  8. An island’s species richness depends on: • island’s isolation • island’s area isolation affects colonization rate area affects extinction rate • colonization and extinction are dynamic • species richness reflects an equilibrium • between colonization and extinction colonization replaces extinct species  species turnover (MacArthur and Wilson, 1967)

  9. Fig. 23.9 Equilibrium Theory of Island Biogeography (MacArthur and Wilson, 1967) species richness: equilibrium between colonization and extinction

  10. As more species accumulate on the island, the immigration rate decreases • good dispersers arrive quickly • poor dispersers arrive slowly • more mainland species have already colonized the island

  11. As more species accumulate on the island, the extinction rate increases • more species available • to become extinct • competition intensifies • as niches get filled up • population size of each species declines • (smaller populations are at a greater risk of extinction)

  12. Species richness decreases with isolation… …and increases with islandarea more niches on large islands fewer species can disperse to distant islands lower equilibrium number of species higher equilibrium number of species

  13. mainland Which island will have higher species richness? Why? Which island will have higher species richness? Why?

  14. Biogeography • geographic patterns of species diversity and distribution • contributes to global biodiversity • reflects patterns of evolution, dispersal, and extinction

  15. Equilibrium theory of Island biogeography • Species richness on islands (or other habitat patches) reflects a dynamic equilibrium between colonization and extinction. • Species richness decreases with island isolation and increases with island area.

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