The Marine Side of a Terrestrial Carnivore: Intra-Population Variation in Use of Allochthonous Resources by Arctic Foxes

Abstract

Inter-individual variation in diet within generalist animal populations is thought to be a widespread phenomenon but its potential causes are poorly known. Inter-individual variation can be amplified by the availability and use of allochthonous resources, i.e., resources coming from spatially distinct ecosystems. Using a wild population of arctic fox as a study model, we tested hypotheses that could explain variation in both population and individual isotopic niches, used here as proxy for the trophic niche. The arctic fox is an opportunistic forager, dwelling in terrestrial and marine environments characterized by strong spatial (arctic-nesting birds) and temporal (cyclic lemmings) fluctuations in resource abundance. First, we tested the hypothesis that generalist foraging habits, in association with temporal variation in prey accessibility, should induce temporal changes in isotopic niche width and diet. Second, we investigated whether within-population variation in the isotopic niche could be explained by individual characteristics (sex and breeding status) and environmental factors (spatiotemporal variation in prey availability). We addressed these questions using isotopic analysis and Bayesian mixing models in conjunction with linear mixed-effects models. We found that: i) arctic fox populations can simultaneously undergo short-term (i.e., within a few months) reduction in both isotopic niche width and inter-individual variability in isotopic ratios, ii) individual isotopic ratios were higher and more representative of a marine-based diet for non-breeding than breeding foxes early in spring, and iii) lemming population cycles did not appear to directly influence the diet of individual foxes after taking their breeding status into account. However, lemming abundance was correlated to proportion of breeding foxes, and could thus indirectly affect the diet at the population scale.

Direct and indirect effects of regional and local climatic factors on trophic interactions in the Arctic tundra

“…Arctic foxes are characterized by high behavioural flexibility, which allows for an important variation in their feeding niche. Tarroux et al () showed that in the presence of a large goose colony, Arctic foxes are more versatile and behave more as a generalist forager than a specialist one. During spring and summer, goose eggs are always part of the fox diet regardless of the variability in lemming abundance between years (Careau et al, ).…”

Long-term monitoring at multiple trophic levels suggests heterogeneity in responses to climate change in the Canadian Arctic tundra

“…Known dens were checked for breeding activity of Arctic and red foxes every year in summer [47]. Since 2003, adult and juvenile Arctic foxes were captured, marked with ear tags and sampled (blood and hairs) in summer for analysis of carbon and nitrogen isotopic ratios [48].…”

“…The nitrogen isotopic ratio in fox blood is used here as a trophic index, assuming that higher d 15 N generally indicates foraging at higher trophic levels [50]. On Bylot Island, a higher d 15 N also reflects stronger reliance of foxes on marine food [48].…”

Interaction webs in arctic ecosystems: Determinants of arctic change?

“…In the arctic terrestrial interaction web such allochthonous resources come from both the marine and the limnic environments. Resources from the marine environment are for instance transferred to the terrestrial ecosystem by many of the terrestrial predators (Therrien et al 2011; Tarroux et al 2012; Gilg et al 2013), and in some cases herbivores, too, make extensive use of marine resources outside the summer season (Hansen and Aanes 2012). The terrestrial system receives input from the limnic ecosystem, through the consumption of freshwater midges by terrestrial spiders (Gratton et al 2008).…”