Historical processes enhance patterns of diversity along latitudinal gradients

Abstract

One of the more vexing issues in ecology is how historical processes affect contemporary patterns of biodiversity. Accordingly, few models have been presented. Two corollary models (centre of origin, time-for-speciation) can be used to make quantitative predictions characterizing the tropical niche conservatism hypothesis and describe diversification as diffusion and subsequent cladogenesis of species away from the place of origin of a higher taxon in the tropics. Predictions derived from such models are: (i) species richness declines toward the periphery of the range of a higher taxon; (ii) taxa are more derived toward the periphery than the centre; (iii) ages of taxa are lower toward the periphery than the centre; and (iv) ages and measures of derivedness are less variable toward the periphery of the range of a higher taxon. I tested these predictions to better understand the formation of one of the most ubiquitous patterns of biodiversity-the latitudinal gradient in species richness. Results indicate well-supported predictions for New World leaf-nosed bats and that diversification has had strong influences on latitudinal gradients of species richness. A better understanding of how evolutionary diversification of taxa contributes to formation of patterns of species richness along environmental gradients is necessary to fully understand spatial variation in biodiversity.

Figure 1

Latitudinal gradients of diversity and phylogenetic characteristics of New World leaf-nosed bat assemblages.

Figure 2

Results from simulation analyses evaluating the degree to which latitudinal gradients in phylogenetic diversity can result from a latitudinal gradient in species richness. (a) Illustrates differences between expected values for empirical (black line) and simulated (grey line) assemblages. (b–d) Illustrate comparisons of the empirical parameter estimates (grey arrows) with the distributions of simulated parameter estimates (black histograms) regarding the coefficient of variation, linear slope and quadratic slope, respectively.