Niche evolution and community assembly.
Ackerly, David1, Webb, Cam2, 1 Department of Biological Sciences, Stanford, CA, United States2 Department of Ecology and Evolutionary Biology, New Haven, CT, United States
ABSTRACT- In the process of community assembly, the interactions of closely related species are of particular interest for the study of competition and the evolution of niche differentiation. We pose a general question: in the course of an evolutionary radiation, do traits related to within-habitat niche differences evolve before or after differentiation of habitat affinity or climatic tolerances? Here we introduce two new methods to test patterns of trait evolution and address this question. The Simultaneous vs. Sequential (SvS) test examines whether evolutionary divergences in two traits tend to occur in concert, with large divergences at the same nodes, or sequentially, with large divergences in one trait associated with smaller divergences in another. If a sequential pattern is detected, the Divergence Order test (DOT) is then used to determine whether divergences in one trait tend to precede the other, or if large divergence events are interleaved at different nodes through time. Both tests are based on modifications of the phylogenetic independent contrasts method, using appropriate randomization methods for significance testing. These two tests are used to examine the evolution of traits related to within- vs. between-habitat niche differentiation in diverse evolutionary radiations. Case studies are drawn from our own research and the literature, including woody plant groups such as California Ceanothus and vertebrate lineages such as Caribbean Anolis and Old World warblers. The results suggest that in relatively recent radiations (within genera or comparable groups), within-habitat niche differences tend to evolve first, followed by differentiation of habitat or geographic range. At deeper levels, however, the patterns may be reversed, with differentiation of major lineages into distinct habitats or climatic regions. Similarities in patterns of niche evolution, especially across plant and animal lineages, suggest common underlying evolutionary processes, reflecting shared biogeographic histories and/or common principles of community assembly and evolution.
Key words: community assembly, phylogeny, niche evolution
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