title: The ecology of individuals: incidence and implications of individual specialization.
abstract: Most empirical and theoretical studies of resource use and population dynamics treat conspecific individuals as ecologically equivalent. This simplification is only justified if interindividual niche variation is rare, weak, or has a trivial effect on ecological processes. This article reviews the incidence, degree, causes, and implications of individual-level niche variation to challenge these simplifications. Evidence for individual specialization is available for 93 species distributed across a broad range of taxonomic groups. Although few studies have quantified the degree to which individuals are specialized relative to their population, between-individual variation can sometimes comprise the majority of the population's niche width. The degree of individual specialization varies widely among species and among populations, reflecting a diverse array of physiological, behavioral, and ecological mechanisms that can generate intrapopulation variation. Finally, individual specialization has potentially important ecological, evolutionary, and conservation implications. Theory suggests that niche variation facilitates frequency-dependent interactions that can profoundly affect the population's stability, the amount of intraspecific competition, fitness-function shapes, and the population's capacity to diversify and speciate rapidly. Our collection of case studies suggests that individual specialization is a widespread but underappreciated phenomenon that poses many important but unanswered questions.
authors.affiliation: Section of Evolution and Ecology, Center for Population Biology, Storer Hall, University of California, Davis, California 95616, USA. dibolnick@ucdavis.edu
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Bolnick
authors.forename: Richard
authors.initials: R
authors.lastname: Svanbäck
authors.forename: James A
authors.initials: JA
authors.lastname: Fordyce
authors.forename: Louie H
authors.initials: LH
authors.lastname: Yang
authors.forename: Jeremy M
authors.initials: JM
authors.lastname: Davis
authors.forename: C Darrin
authors.initials: CD
authors.lastname: Hulsey
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Forister
mesh_terms: D000818:Animals; D005075:Biological Evolution; D003247:Conservation of Natural Resources; D004463:Ecology; D014644:Genetic Variation; D008954:Models, Biological; D018401:Sample Size; D013045:Species Specificity