Geographic Isolation and the Amazon Rainforest
The fact that biodiversity is greatest at the equator has resulted in the commonly held view that the destruction of one square mile of habitat destroyed in the tropical rainforests potentially endangers at least ten times as many species as similar area loss in temperate regions.
Until recently, this opinion directed conservation efforts by and large to tropical forest. However, an analysis of endemic and nonendemic taxa in South America found a simple relationship; the dry lands, almost twice as extensive as the Amazon lowlands, support more endemic taxa.
Drylands are often considered areas of low diversity, but for mammals they are the most species-rich area on the continent.
This diversity evolved during the Pleistocene glaciations. The area of the Amazon where the dry lands are found was, previous to the Pleistocene, a series of continuous geographic ranges. Sets of closely related species and subspecies evolved when fragmentation of the habitat occurred due to glaciations. This occurred when fauna became isolated due to the fragmentation, and underwent a classic geographic isolation mechanism (Mares, 1992).
The current fragmentation occurring in the rainforests due to human activity will unfortunately not result in such a new explosion of species. The rate at which the changes in habitat are occurring are much too rapid; the Pleistocene glaciations took tens of thousands of years; apart from a few isolated areas, the rain forest will likely have been completely eradicated within fifty years. Also, fragmentation of an environment does not always result in speciation; for more information, click here!
