The Alternative Prey Hypothesis (APH) states that predators switch to relatively more abundant prey when their main prey is scarce. In the High Arctic, lemming population cycles indirectly affect predation risk on alternative prey such as shorebird nests as they share a main predator, the arctic fox. In this study, we examined the indirect effects of arvicoline rodent cycles on alternative prey in the Subarctic where arctic and red fox coexist as predators of primary (lemmings, voles) and alternative prey (shorebird nests). Using 10 years of field data, our results indicate that interannual variation in daily nest survival of Dunlin was best explained by an interactive effect of arvicoline rodent abundance and arctic fox (not red fox) abundance. During high rodent years, shorebird nest survival appeared to be buffered from variation in arctic fox abundance but when rodents were absent, nest survival declined. We found no relationship between shorebird nest survival and red fox abundance despite red foxes being found in much higher abundance in the study area. Our results indicate that despite the presence of other predators and multiple primary prey species, predator-mediated interactions common to High Arctic sites, still hold true for the Subarctic in regards to the arctic fox, arvicoline rodents and shorebirds.
Resource fluctuation is a major driver of animal movement, influencing strategic choices such as residency vs nomadism, or social dynamics. The Arctic tundra is characterized by strong seasonality: resources are abundant during the short summers but scarce in winters. Therefore, expansion of boreal-forest species onto the tundra raises questions on how they cope with winter-resource scarcity. We examined a recent incursion by red foxes (Vulpes vulpes) onto the coastal tundra of western Hudson Bay, an area historically occupied by Arctic foxes (Vulpes lagopus) that lacks access to anthropogenic foods, and compared seasonal shifts in space use of the two species. We used 4 years of telemetry data following 8 red foxes and 11 Arctic foxes to test the hypothesis that the movement strategies of both species are primarily driven by temporal variability of resources. We also predicted that the harsh tundra conditions in winter affect red foxes more than Arctic foxes, which are adapted to this environment. Dispersal was the most frequent winter movement strategy in both fox species, despite its association with high mortality (winter mortality was 9.4 times higher in dispersers than residents). Red foxes consistently dispersed towards the boreal forest, whereas Arctic foxes primarily used sea ice to disperse. Home range size of red and Arctic foxes did not differ in summer, but resident red foxes substantially increased their home range size in winter, whereas home range size of resident Arctic foxes did not change seasonally. As climate changes, abiotic constraints on some species may relax, but associated declines in prey communities may lead to local extirpation of many predators, notably by favoring dispersal during resource scarcity.
Predators are widely recognized for their irreplaceable roles regulating the abundance and altering the traits of lower trophic levels. Predators also have irreplaceable roles in shaping community interactions and ecological processes via highly localized pathways, irrespective of their influence on prey density or behavior. We synthesized empirical and theoretical research describing how predators have indirect ecological effects confined to discrete patches on the landscape, processes we have termed patchy indirect effects of predation. Predators generate patchy indirect effects via three main pathways: generating and distributing prey carcasses, creating biogeochemical hotspots by concentrating nutrients derived from prey, and killing ecosystem engineers that create patches. In each pathway, the indirect ecological effects are limited to discrete areas with measurable spatial and temporal boundaries (i.e., patches). Our synthesis reveals the diverse and complex ways that predators indirectly affect other species via discrete patches, ranging from mediating scavenger interactions to interspecific parasite/disease transmission risk, and from altering ecosystem biogeochemistry to facilitating local species biodiversity. We also show how existing multi-scale ecological frameworks (metapopulation, meta-ecosystem, and patch dynamics concepts) offer insight into the mechanisms underlying the formation of these patches within ecosystems. We then provide basic guidelines on how these effects can be quantified at both the patch and landscape scales, and discuss how these predator-mediated patches ultimately increase landscape heterogeneity and contribute to ecosystem functioning. Whereas density- and trait-mediated indirect effects of predation generally occur through population-scale changes, patchy indirect effects of predation occur through individual- and patch-level pathways. Our synthesis provides a more holistic view of the functional role of predation in ecosystems by addressing how predators create patchy landscapes via localized pathways, in addition to influencing the abundance and behavior of lower trophic levels.