The implicit assumption of symmetry and the species abundance distribution

Abstract

Species abundance distributions (SADs) have played a historical role in the development ofcommunity ecology. They summarize information about the number and the relativeabundance of the species encountered in a sample from a given community. For yearsecologists have developed theory to characterize species abundance patterns, and the studyof these patterns has received special attention in recent years. In particular, ecologists havedeveloped statistical sampling theories to predict the SAD expected in a sample taken froma region. Here, we emphasize an important limitation of all current sampling theories: theyignore species identity. We present an alternative formulation of statistical sampling theorythat incorporates species asymmetries in sampling and dynamics, and relate, in a generalway, the community-level SAD to the distribution of population abundances of the speciesintegrating the community. We illustrate the theory on a stochastic community model thatcan accommodate species asymmetry. Finally, we discuss the potentially important role ofspecies asymmetries in shaping recently observed multi-humped SADs and in comparisonsof the relative success of niche and neutral theories at predicting SADs