Biogeographic Diversity

Biogeographic diversity refers to the relationship between the evolutionary history of the biota of a region and the geological and geographic history of that region. Analyses of biogeographic diversity include two fields (Wiley, 1981):

Historical biogeography. This is the study of spatial and temporal distributions of organisms (usually species or higher taxonomic ranks); it attempts to provide explanations for these distributions based on earth history events.

Ecological biogeography. Ecological bio-geography is the study of the dispersal of organisms (usually individuals or populations) and the mechanisms that influence them.

Studies of historical biogeography are important for describing what are called biogeo-graphic provinces, regions defined by their characteristic flora and fauna. For example, examination of the freshwater fish fauna of South America has revealed several distinct faunistic regions, such as the Magdalenean, Orinoco-Venezuelan, Guyana-Amazonian, Paranean, and Patagonian (Gery, 1969). These regions were isolated from each other at various times over the last 90 million years of South America's geological history, because of events such as the formation of inland seaways and the Andean mountain range (Lundberg et al., 1998). Consequently, distinct fish faunas evolved in these regions. According to historical biogeography, the evolutionary history of the fish faunas, and their current distributions, can be explained by the geological history of the continent. However, historical biogeography is not the complete explanation. Ecological biogeographical studies show that recent dispersal of some species has occurred between areas. In addition, some groups of marine fishes have invaded the fresh-waters of South America.

Historical biogeography also explains the diversity of species distributions between continents. For example, different species of freshwater lungfishes are found in Australia, Africa, and South America. This disjunct distribution occurs because these continents were joined (as the supercontinent Gondwanaland) about 90 million years ago. It is presumed that the ancestor to the different species was distributed across Gondwanaland; speciation, resulting in the current taxa, occurred after the breakup of the continents.

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