Monday, August 6, 2007

Biogeorgraphic Distributions

The geographic distributions of species can be of a number of types
Consider the distribution of three species of toucans in the genus Ramphastos.
• Endemic distributions
Two of the species, R. vitellinus and R. cluminatus , have endemic distributions: they are limited to a particular area. Endemic distributions can be more or less widespread.
• Cosmopolitan distributions
The extreme case of species that are found on all continents of the globe are called cosmopolitan. The pigeon, for example, is found on all continents except Antarctica; on a strict definition, the pigeon (pictured opposite) might not be allowed to be cosmopolitan, but the term is usually intended less strictly - and the pigeon is called a cosmopolitan species.
• Disjunct distributions
Other species, like R. ariel , are not confined to a single area, but are distributed in more than one region with a gap between them: these are called disjunct distributions.
Maps can be drawn for a taxonomic group at any Linnaean level: just as species have geographic distributions, so too do genera, families, orders. Biogeography aims to explain the distributions of the higher taxa too, in addition to those of species; and different explanatory processes are often appropriate at different levels.
Short-term movements of individuals influence the distributions of populations and species, whereas slower acting geological processes may control the biogeography of higher taxa.

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