Environmental determinants of biodiversity

• Richard D. Stevens

Abstract
Understanding the mechanistic bases of patterns in biodiversity has challenged ecologists and evolutionary biologists alike for more than a quarter of a century (Rosenzweig 1995). Although the ubiquity of gradients in species richness is well documented at coarse scales of resolution, it is unclear to what extent patterns are recapitulated at the level of local communities or for any other aspect of biodiversity (Stevens and Willig 2001). Biodiversity represents the totality of variation in living things (Tilman 2000). Thus, it is likely that no one measure such as species richness, or any one perspective, such as that of taxonomic diversity, can provide a comprehensive characterization. Investigations that simultaneously explore fundamental components of biodiversity (i.e., taxonomic, functional, or phylogenetic diversity) will allow for analyses that provide deeper, more comprehensive understanding regarding the distribution of biota across space and time. Although secondary gradients (e.g., latitudinal diversity gradients) have been described ubiquitously, much less is known about the primary environmental gradients or suite of gradients that cause such patterns. Numerous biotic and abiotic characteristics vary spatially in different but correlated ways. Distinguishing the relative contributions of a number of environmental characteristics to gradients in biodiversity will contribute substantially to our understanding of ecology, biogeography, and evolution. Moreover, resolution of the effects of primary gradients on the spatial distribution of biodiversity may also greatly enhance our understanding of the mechanistic basis of secondary gradients such as those described for latitude.

Vazquez, Diego; Stevens, Richard. In press. The latitudinal gradient in niche breadth: Concepts and evidence. American Naturalist.