Introduction: Merging Evolutionary and Ecological Approaches to Understanding Geographic Gradients in Species Richness

Abstract

One of the most exciting recent developments at the interface between ecology and evolution has been community phylogeny, which was introduced in an annual review by Webb et al. (2002) and is the subject of a recent special issue of Ecology (vol. 87, suppl., July 2006). Community phylogeny merges the ecologist’s traditional concern with the distribution of traits among coexisting taxa with phylogenetic approaches to understanding where and when those traits evolved. This fusion makes it possible to ask how the distribution of functional traits within local communities arises from both ecological processes, such as habitat selection and niche partitioning, and evolutionary ones, such as phylogenetic origin and adaptive response to the environment, including other species. The result is what its proponents call the “new natural history” (Webb et al. 2006): an understanding of the ecological community that is informed by history and biogeography in addition to the contemporary distribution and ecological interactions of the component species. The goal of this special issue, and of the symposium from which it arose, is to extend this synthesis to understanding patterns in species richness along geographic and environmental gradients. Some of the most venerable questions in ecology concern how the number of coexisting species varies with latitude, elevation, productivity, area, isolation, and the frequency and severity of disturbance. Ecologists typically study factors that control diversity from a geographic perspective, analyzing numbers of species in units such as study plots, islands, or geographic regions regardless of the species’ taxonomic ori-