Different biogeographic areas can be quantified for levels of similarity in their biota

Different biogeographic areas can be quantified for levels of similarity in their biota

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Different biogeographic areas can be quantified for levels of similarity in their biota (biota=general term for flora+fauna, includes microbes). N 1 = number of species (or other taxonomic unit) in one region, N 2 = number in another region (N 1 < N 2 ) and C = number of same species. Index of Similarity = C/N 1 . For Australia: New Guinea, I.S. = 0.93 (93%), while Australia: Philippines, I.S. = 0.50 (50%). See table 18.1, pg 511. This provides a simple quantification of Wallace's Line. How do we account for these patterns? Early biogeographers tended to invoke dispersal (prior to knowledge about continental drift). Potential problems: ad hoc , could pull dispersal out of a hat whenever you needed to explain a peculiar distribution. Leads to many wild scenarios of " gravid females " (pregnant, or inseminated females carrying eggs) making there way to distant regions.
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Unformatted text preview: Muddyfooted duck carrying propagules in its feet; land bridges invoked connecting disjunct regions. Criticized by many as unscientific : cannot falsify the dispersal hypothesis because it is something we'll never know for sure, thus is of no explanatory power. Nevertheless, all these types of events probably have occurred at some point. The Bering land bridge is well documented as an avenue of dispersal; the Opossum (a marsupial) in North America clearly dispersed here from South America via the Isthmus of Panama (see below); oceanic islands have life on them and it must have gotten there by dispersal. Several modes of dispersal can be described: Corridors between two regions on the same land mass, Filter bridges as selective connections between two areas, Sweepstakes as rare chance events (e.g. muddyfooted duck)....
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This note was uploaded on 11/06/2011 for the course BIO BSC1010 taught by Professor Gwenhauner during the Fall '10 term at Broward College.

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