BOLNICK, D I; SVANBACK, R; FORDYCE, J A; YANG, L H; DAVIS, J M; HULSEY, C D; FORRISTER, M A; University of California, Davis; Uppsala University; University of Tennessee; University of California, Davis; University of California, Davis; University of California, Davis; University of California, Davis; : Comparative approaches to intra-population niche variation

Ecologists tend to treat a species as an ecologically and functionally homogenous group of individuals. This assumption greatly simplifies empirical and theoretical studies of competition, population dynamics, and community dynamics such as food web cascades, but is rarely tested. In fact, conspecific individuals, living in the same location, may vary widely in their resource use. Such individual-level variation, or �individual specialization� appears to be widespread, having been documented in over 100 species, including gastropods, crustaceans, insects, and all classes of vertebrates. While it is now clear that individual specialization exists, it remains uncertain how common it is, under what ecological conditions individual niche variation will be more or less pronounced, and what are the ecological and evolutionary implications of this variation. Answering such questions requires a quantitative framework that will allow comparative studies of individual specialization both within, and among species. I outline and assess several alternative methods for measuring the degree of individual specialization, and illustrate their application in several systems, with particular emphasis on the kinds of comparative questions that can be answered with these methods.