Abstract
To quantify the ecological effects of predator populations, it is important to evaluate how population-level specializations are dictated by intra- versus inter-individual dietary variation. Coastal habitats contain prey from the terrestrial biome, the marine biome and prey confined to the coastal region. Such habitats have therefore been suggested to better support predator populations compared to habitats without coastal access. We used stable isotope data on a small generalist predator, the arctic fox, to infer dietary strategies between adult and juvenile individuals with and without coastal access on Iceland. Our results suggest that foxes in coastal habitats exhibited a broader isotope niche breadth compared to foxes in inland habitats. This broader niche was related to a greater diversity of individual strategies rather than to a uniform increase in individual niche breadth or by individuals retaining their specialization but increasing their niche differentiation. Juveniles in coastal habitats exhibited a narrower isotope niche breadth compared to both adults and juveniles in inland habitats, and juveniles in inland habitats inhabited a lower proportion of their total isotope niche compared to adults and juveniles from coastal habitats. Juveniles in both habitats exhibited lower intra-individual variation compared to adults. Based on these results, we suggest that foxes in both habitats were highly selective with respect to the resources they used to feed offspring, but that foxes in coastal habitats preferentially utilized marine resources for this purpose. We stress that coastal habitats should be regarded as high priority areas for conservation of generalist predators as they appear to offer a wide variety of dietary options that allow for greater flexibility in dietary strategies.
Highlights
The dietary specialization of predator populations has far reaching consequences for their ecological impacts
Our study focuses on three main questions: I) do arctic foxes from coastal and inland habitats differ in their isotope niche? II) how do any such habitat related differences in isotope niches compare to individual isotope niche breadth in foxes from each habitat? III) how are habitat related differences both in population and individual isotope niche breadth affected by the life stage of the animal?
Adult foxes from the coastal habitat had a broader isotope niche breadth compared to adult foxes from the inland habitat
Summary
The dietary specialization of predator populations has far reaching consequences for their ecological impacts. In a highly influential study, Roughgarden [1] highlighted that the dietary breadth exhibited by a predator population may depend on the specialization of individual predators, and on dietary overlap between individuals. Dietary breadth is typically broader for predator populations in environments with larger prey diversity [5]. Environments with a varied prey base are often more productive and can better sustain predator populations [6]. Coastal habitats usually provide high prey diversity with prey from both the terrestrial and the marine biome as well as typically coastal prey. Many species of terrestrial carnivores utilize this diversity for feeding, and coastal habitats can sustain higher predator densities than terrestrial regions [7,8]. To what extent such an expanded foraging niche in costal habitats is caused by a diversification of the diet of all individuals, by an increased individual niche separation or by an increased range of dietary strategies has so far rarely been tested with empirical data
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