Abstract
The role of ecological limits in regulating the distribution and diversification of species remains controversial. Although such limits must ultimately arise from constraints on local species coexistence, this spatial context is missing from most macroevolutionary models. Here, we develop a stochastic, spatially explicit model of species diversification to explore the phylogenetic and biogeographic patterns expected when local diversity is bounded. We show how local ecological limits, by regulating opportunities for range expansion and thus rates of speciation and extinction, lead to temporal slowdowns in diversification and predictable differences in equilibrium diversity between regions. However, our models also show that even when regions have identical diversity limits, the dynamics of diversification and total number of species supported at equilibrium can vary dramatically depending on the relative size of geographic and local ecological niche space. Our model predicts that small regions with higher local ecological limits support a higher standing diversity and more balanced phylogenetic trees than large geographic areas with more stringent constraints on local coexistence. Our findings highlight how considering the spatial context of diversification can provide new insights into the role of ecological limits in driving variation in biodiversity across space, time, and clades.
Highlights
Our models show that even when regions have identical diversity limits, the dynamics of diversification and total number of species supported at equilibrium can vary dramatically depending on the relative size of geographic and local ecological niche space
Increases in diversity over geological time have often been linked to the accessing of novel regions of geographic or ecological niche space (Benton 2009), while differences in richness between clades and regions are typically associated with differences in environmental conditions or geographic area that are thought to limit the total number of species that can be packed within a region (Rabosky 2009; Ezard et al 2011)
We model the spatial dynamics of diversification on a two-dimensional gridded domain where each cell represents a local assemblage and where the area of the region (A) sets an upper bound on the number of populations or geographic range size of each species
Summary
The role of ecological limits in regulating the distribution and diversification of species remains controversial Such limits must arise from constraints on local species coexistence, this spatial context is missing from most macroevolutionary models. Our models show that even when regions have identical diversity limits, the dynamics of diversification and total number of species supported at equilibrium can vary dramatically depending on the relative size of geographic and local ecological niche space. It has been argued that such limits–if they even exist–do not impose an important constraint on diversity, which instead may be largely controlled by historical factors (Wiens 2011) According to this argument, variation in diversity primarily involves nonequilibrium explanations, including differences in the time available for diversification, rates of colonization, speciation, or extinction (Ricklefs and Bermingham 2001; Wiens and Donoghue 2004; Jetz and Fine 2012). Evolution published by Wiley Periodicals, Inc. on behalf of The Society for the Study of Evolution
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