Pleistocene refugia

Pleistocene refugia - separated in space Continents must...

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Pleistocene refugia nicely illustrate how vicariance and dispersal may need to be invoked to explain current distributions. Glacial ice sheet forced species to new distributions (vicariance event), after glacial retreat, the separated forms dispersed to previous regions (or wider distribution). Relative roles of dispersal and vicariance in determining species distributions can vary widely with a given species dispersal abilities (see fig. 18.3, 18.4 pg. 514-515). Essential to realize that dispersal has two components: the ability to move and the ability to become established . These two properties may not be "optimized" in the same organism. Continental Drift as source of vicariance events. Evidence for continental drift provided by disjunct fossil specimens: Mesosaurus in South America and Africa. Illustrates the space and time component of biogeography since the strata reflect the same time (old) but are widely
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Unformatted text preview: separated in space. Continents must have moved. (Fig. 18.5, pg. 517). Major stages of the split-up of continents: Pangaea formed in Permian (> 250 MyBP) and began to break up in the Triassic (200 MyBP). Laurasia and Gondwana separated at the Tethys seaway (135 MyBP). Tropical corals, sea grasses and mangroves are related in Americas and old world tropics reflecting earlier Tethyan distribution . Gondwana began to break up about 80 MyBP and the major continents were separated by late Cretaceous (65 MyBP). India smashed into Asia crating the Himalayas. As the continents separated vicariance events abounded and the fauna of various continents became increasingly Provincialized . The South American mammals had many unique forms with respect to the North American Fauna. Marsupials in Australian zone are distinct form of mammal....
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