Evolution by neutral and niche-based ecological processes in simulated and real metacommunities

Background/Question/Methods

Community structure results from not only from the sorting processes caused by species interactions today, but also from the macroevolutionary processes of speciation and extinction that shaped the diversification of lineages leading to today’s species.  I present the analysis of a macroevolutionary model of metacommunity assembly that places speciation and extinction in an ecological context.  Using this model I vary the degree to which new species are ecologically similar to their progenitors to simulate different modes of speciation (e.g., speciation via ecological differentiation vs. hybridization vs. sexual selection).  After entering the metacommunity, species are driven extinct by interactions with other species according to Lotka-Volterra dynamics.  I compare the results of this theoretical analysis to real data of community structure, fossil histories of marine clades, and macroevolutionary dynamics from 350 molecular phylogenies culled from the literature. 

Results/Conclusions

Results of the model show that when new species can be ecologically very different from their progenitors (e.g., ecological speciation), lineage diversification slows appreciably over the history of a clade.  Initially new species fill empty niche space, but as niche space fills, only species replacements occur and overall species richness came to a dynamical equilibrium.  As a result diversification rate is rapid initially but slows appreciably over most of clade’s history.  Random communities assembled with this model show patterns in their fossil record that are consistent with real fossil histories accumulated at the genus (and above) level, with ~50% of the clades represented in the molecular phylogeny dataset.  In contrast, when new species in the model communities were not very different from their progenitors (e.g., sexual selection), species richness increased over the entire history of the clade.  As a result, the apparent diversification rate showed an acceleration as expected over the history of the clade.  These dynamics matched nearly identically a number of fossil histories of clades accumulated at the species level, and to the macroevolutionary dynamics of ~20% of the clades in the molecular systematics data set. 

This analysis shows that the ecological processes operating as lineages diversify to assemble communities leave clear signatures in both the fossil histories and the molecular systematics of clades.  Combining ecological experiments of extant communities with fossil and systematic data provides the most comprehensive test of the processes structuring ecological communities.