Disentangling the relative influences of global drivers of change in biodiversity: A study of the twentieth‐century red fox expansion into the Canadian Arctic

Abstract

The poleward range shift of the red fox (Vulpes vulpes) > 1,700 km into the Arctic is one of the most remarkable distribution changes of the early twentieth century. While this expansion threatens a smaller arctic ecological equivalent, the arctic fox (Vulpes lagopus), the case became a textbook example of climate‐driven range shifts. We tested this classical climate change hypothesis linked to an important range shift which has attracted little research thus far. We analysed Canadian fur harvest data from the Hudson's Bay Company Archives (14 trading posts; 1926–1950), testing hypotheses based on changes in summer and winter climates. Summer warming might have triggered a bottom‐up increase in ecosystem productivity, while winter warming might have lowered thermal stress, both favouring red fox expansion. Additionally, we evaluated the hypothesis that red fox expansion was driven by the appearance of human sedentary sites (n = 110) likely bringing food subsidies into the unproductive tundra. Analysis of red fox expansion chronologies showed that expansion speed was higher during warmer winters. However, the expansions occurred under both cooling and warming trends, being faster during cooler summers in the Baffin Island region. The increasing proportion of red fox in fox fur harvests was best explained by human activity, while generalized linear mixed models also revealed a marginal effect of warmer winters. Generalized additive models confirmed human presence as the most important factor explaining rates of change in the proportion of red fox in fox fur harvests. Using historical ecology, we disentangled the relative influences of climate change and anthropogenic habitat change, two global drivers that transformed arctic biodiversity during the last century and will likely continue to do so during this century. Anthropogenic food subsidies, which constitute stable food sources, facilitated the invasion of the tundra biome by a new mammalian predator and competitor, with long‐term consequences that still remain to be understood.

Foxes engineer hotspots of wildlife activity on the nutrient-limited Arctic tundra

“…Arctic foxes in the southern Arctic are threatened with range contraction in response to the northward expansion of red foxes (Elmhagen et al 2017, Gallant et al 2020) and anthropogenic climate change (Verstege 2016). Our results suggest that the potential disappearance of Arctic foxes could affect other wildlife via reduced ecosystem engineering and resource provisioning.…”

Highways associated with expansion of boreal scavengers into the alpine tundra of Fennoscandia

“…This suggests that roads indeed may serve as landscape features that benefit boreal generalist species and facilitate their presence in otherwise low productive habitats. Several studies highlight the importance of subsidies in the advancement of boreal generalists into alpine and arctic tundra (Gallant, Lecomte, & Berteaux, 2019; Restani, Marzluff, & Yates, 2001; Sokolov, Sokolova, Ims, Brucker, & Ehrich, 2016), and roads are known to be an important source of subsidies for scavengers or carrion‐feeders (Knight, Knight, & Camp, 1995; Oxley, Fenton, & Carmody, 1974). Although traffic volume, and thus the potential amount of generated subsidies, in our study areas was relatively low compared to other studies (e.g.…”

“…However, this source is quite limited in space and our results indeed suggest that most of the red fox activity was within 1–2 km from the highways. Utilization of areas close to roads was generally higher for red foxes than arctic foxes in years where rodent abundance crashed, implying that external subsidies may be important for red foxes within alpine areas during winter and when abundance of natural prey is low, where carcasses and food of anthropogenic origin may sustain the red fox population (Gallant et al., 2019; Killengreen et al., 2011).…”

Scavenger community structure along an environmental gradient from boreal forest to alpine tundra in Scandinavia

“…As several recent studies have pointed out, resource subsidies, including carrion, could facilitate generalist scavenger establishment and increased abundance in tundra ecosystems (Gallant et al., 2020; Henden et al., 2014; Sokolov et al., 2016). Our results add support to earlier studies pointing to carrion as an important subsidy for generalist scavengers during harsh winter conditions (Jędrzejewski & Jędrzejewska, 1992; Pulliainen & Ollinmäki, 1996; Temple, 1974).…”