Variability in marine resources affects arctic fox population dynamics

Abstract

Summary 1.Terrestrial predators in coastal areas are often subsidized by marine foods. In order to determine the potential impact on terrestrial prey, the numerical response of predators to each food source must be determined. 2. In winter, arctic foxes ( Alopex lagopus ) may forage on the frozen Arctic ocean and scavenge carcasses of seals killed by polar bears ( Ursus maritimus ), but the importance of this food source and its effect on the population cycles of arctic foxes and lemmings (their primary prey) are unclear. 3. I estimated the marine component of the late winter diet of arctic foxes near Churchill, Manitoba, using stable-carbon isotope analysis, and compared these estimates to abundance of arctic foxes and collared lemmings ( Dicrostonyx richardsoni ). 4. From 1994 to 1997, fox density varied with lemming abundance, but following a decline, fox abundance began increasing before lemmings. During this increase marine foods were consumed more than in other years, with over two-thirds of food intake from marine sources. 5. Arctic and red fox ( Vulpes vulpes ) harvests in the 1980s to 1990s were correlated with published estimates of polar bear body mass, which varies with seal productivity. However, this relationship disappeared during high lemming years. 6. Thus, variation in marine productivity affects arctic fox abundance, especially when their primary prey are scarce, and this numerical response of arctic foxes to marine resources and lemmings suggests that increased predation by arctic foxes subsidized by seal carrion may delay the recovery of low lemming populations.

Effect of resource subsidies on predator–prey population dynamics: a mathematical model

“…These allochthonous resources, or resource subsidies, can strongly affect the abundance and space use of consumers in recipient ecosystems, with cascading effects on in situ resources [28,30,38,50,53]. However, the impact of resource subsidies on recipient communities can be affected by several factors, including the productivity of the donor and recipient habitats, amount of input, trophic level receiving the input, and temporal variability in subsidy input rates [29,37,55,58].…”

Effects of regime shifts on the population dynamics of the grey-sided vole in Hokkaido, Japan

“…Stenseth et al 1998) as well as elsewhere in Europe (Tkadlec & Stenseth 2001) and in Japan (Saitoh et al 1997, Stenseth et al 2002a, 2003. Delayed density dependence is generally strong and prevails in Fennoscandia, whereas direct density dependence becomes weaker toward the north (Bjørnstad et al 1995).…”

“…M. nivalis), which is an agent of delayed density dependence, may have been more important in Regime 2 than in Regime 1, and consequently the vole populations in Hokkaido may have exhibited cyclic dynamics during Regime 2. Roth (2003) demonstrates that marine resources affect arctic fox abundance in Canada and suggests that they may delay the recovery of low lemming populations (see Rose & Polis 1998 for other examples). Inputs of allochthonous resources could modify food-web dynamics (Polis et al 1997, Huxel & McCann 1998, Jefferies 2000.…”

“…length of the breeding season or non-breeding winter period) and density dependence agents (e.g. predators, food and disease), we would be able to predict changes in dynamic pattern, since the structure of density dependence is influenced by seasonality , 2002a, 2003.…”

“…Based on our previous studies, the features of population dynamics of the Hokkaido vole can be summarized as follows (Saitoh 1987, 1998, 1999, 1998, 2002a, 2003, Saitoh et al 1997, 1998, 1999, 2003:…”