Historical processes enhance patterns of diversity along latitudinal gradients.
Stevens, Richard*,1, 1 Department of Biological Sciences, Baton Rouge, LA
ABSTRACT- Much of the current debate surrounding the mechanistic basis to patterns of diversity can be attributed to the relative degree to which either historical or contemporary mechanisms determine empirical gradients. Nonetheless, few models describing how historical processes can contribute to contemporary patterns of diversity have been presented. Two such models (i.e., center of origin and time-for-speciation) describe diversification as a process of nonrandom diffusion and subsequent cladogenisis of species away from the particular place of origin of a higher taxon. Predictions of such models are: (1) species richness declines toward the periphery of the range of a higher taxon, (2) the amount of sequence divergence between a taxon and the putative ancestor of the entire clade is greatest toward the periphery than the center, (3) age of taxa is lower toward the periphery than the center, and (4) variance of sequence divergences and ages is highest toward the center and lower toward the periphery of the range of the higher taxon. I tested these predictions in an attempt to better understand the role of historical processes in the formation of one of the most ubiquitous patterns of biodiversity -- the latitudinal gradient in species richness. Results indicate that predictions are well-supported for New World leaf-nosed bats and that diversification has had strong influences on latitudinal gradients of species richness. Contemporary and historical processes likely interact to produce cotemporary patterns of biodiversity. Nonetheless, the interdependence of contemporary and historical environments prevents the independent implication of either type of process in determining present-day patterns of diversity. Indeed, a better understanding of how the evolutionary diversification of taxa contributes to the formation of patterns of species richness along environmental gradients is necessary to fully understand spatial variation in biodiversity.
Key words: Biodiversity, Latitudinal Gradient, Diversification
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