Abstract
Variability in resource use defines the width of a trophic niche occupied by a population. Intra-population variability in resource use may occur across hierarchical levels of population structure from individuals to subpopulations. Understanding how levels of population organization contribute to population niche width is critical to ecology and evolution. Here we describe a hierarchical stable isotope mixing model that can simultaneously estimate both the prey composition of a consumer diet and the diet variability among individuals and across levels of population organization. By explicitly estimating variance components for multiple scales, the model can deconstruct the niche width of a consumer population into relevant levels of population structure. We apply this new approach to stable isotope data from a population of gray wolves from coastal British Columbia, and show support for extensive intra-population niche variability among individuals, social groups, and geographically isolated subpopulations. The analytic method we describe improves mixing models by accounting for diet variability, and improves isotope niche width analysis by quantitatively assessing the contribution of levels of organization to the niche width of a population.
Highlights
The niche concept, which provides a tractable measure of the environment encountered by organisms, figures prominently in ecological and evolutionary theory [1–3]
Examining the niches of mainland and island birds, Van Valen proposed that population niche width expansion can occur via increased among-individual variation in foraging, such as he observed in island bird populations that were released from interspecific competition
In this paper we describe a novel analytic framework for using stable isotope data to infer the prey composition of consumer diets while simultaneously estimating variability in diet composition across multiple levels of the consumer’s population structure
Summary
The niche concept, which provides a tractable measure of the environment encountered by organisms, figures prominently in ecological and evolutionary theory [1–3]. The niche of a species is the collective response of individuals, groups, and subpopulations to complex ecological and evolutionary processes. Niche differences across relevant levels of population structure collectively comprise a niche of a species or population. Examining the niches of mainland and island birds, Van Valen proposed that population niche width expansion can occur via increased among-individual variation in foraging, such as he observed in island bird populations that were released from interspecific competition. Bolnick et al [6] reviewed support for the concept of the ‘individual niche’, and identified evidence from 97 species across a broad range of taxa. In some of these cases, among-individual foraging niche accounted for most of the total population niche width
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