| Summary: | The niche concept, which provides a tractable measure of the environment encountered by organisms, figures prominently in ecological and evolutionary theory. Although neglected, valuable information may be gained by examining niche variation at hierarchies nested within its historical roots at the species level. Herein I examine intrapopulation variation in foraging niche - at the sub-population, social group, and individual levels - and investigate its ecological causes and evolutionary consequences in a predator-prey system within a marine archipelago. I used two analytical techniques. My primary tool, stable isotope analysis of δ13C and δ15N, coalesces the multiple dimensions of the foraging niche into two dimensions. Variation in prey remains identified in faeces served as an independent data set. I examined how different levels of resource availability over space and time as well as competition could account for observed intrapopulation niche variation in a terrestrial carnivore (wolf, Canis lupus). Major shifts in resource use were associated with biogeographic region, from dominance of in situ terrestrial resources (deer, Odocoileus hemionus) on the mainland to prevalence of allochthonous (marine) resources islands. The probability of deer remains in wolf faeces declines as a function of island isolation. Correspondingly, marine enrichment in isotopic signatures of wolves increases with isolation. Estimates of marine biomass assimilation vary from roughly 25 to 50 to 75% among mainland, inner, and outer island sub-populations respectively How animals select resources also can contribute to intrapopulation variability in niche. A `resource selection' approach indicated that, when available, wolves select spawning salmon (Oncorhynchus spp.) over deer. Although only available during autumn, salmon contribute up to 25% of biomass assimilation in wolves over the 6 month period for which it was estimated. Moreover, previously undocumented salmon hunting by wolves I report identifies them as among a few primary ...
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