Amazonian Speciation: A Necessarily Complex Model

Abstract

Amazonian speciation will not be explained entirely by any single simple model of vicariance or climatic change. The refugial hypothesis is rejected in favour of a more complex evolutionary history. Pre-Quaternary vicariance events appear to have established the major regional divisions of species complexes. Quatemary speciation, and the redistri- bution of existing species, are likely to be superimposed upon this existing pattern, accounting for modem biogeographic patterns. The forcing function driving Quaternary speciation is a combination of glacial age cooling, reduced atmospheric C02, and moderate reductions in precipitation. It is suggested that the central Amazonian forests did not fragment during glacial times, but that populations within forests without modem analogue were repeatedly disrupted by climatic change. The centres of endemism employed to support the concept of unchanging refugia are suggested to have been areas not of maximal stability but of maximal disturbance.