Climate significantly affects trophic interactions, and rapid changes to climate can produce predicted or unanticipated effects on the organization and function of an ecosystem (Sala et al. 2000; Tylianakis et al. 2007). Our knowledge of the effects of climate change varies across trophic levels, and a meta-analysis by Tylianakis et al. (2008) suggested predator-prey interactions were less studied than interactions between herbivores and plants. Predators have a vital ecological role in regulating prey populations and reducing the spread of disease (Ostfeld and Holt 2004). Thus, predator responses to climate change will add to our overall understanding of how climate change affects ecosystems.
Climate warming is disproportionately intense in polar regions, with even more extreme warming recently (Post et al. 2009; Rantanen et al. 2022). Warming temperatures and a longer growing season are mechanisms that predict further range expansion of southern species into the Arctic (Post et al. 2009). The southern edge of Arctic fox (Vulpes lagopus) and northern extent of red fox (V. vulpes) ranges overlap, but a warming climate may support a growing red fox population, generating greater resource competition between the two species (Frafjord et al. 1989; Tannerfeldt et al. 2002; Rodnikova et al. 2011). Red foxes are larger than Arctic foxes and can overtake Arctic fox dens and kill Arctic foxes (Elmhagen et al. 2017). An increase in red fox productivity may promote population declines of Arctic fox.
Climate change may also influence predator population dynamics through altered prey habitats and consequently the availability of prey. A warming climate has instigated changes to the cryosphere, including reduced snow cover across the Northern Hemisphere, reduced sea-ice extent, earlier sea-ice breakup, and later freeze-up of sea ice in Hudson Bay (Brown et al. 2010; Comiso 2012; Lunn et al. 2016). These alterations to the climate and cryosphere can impact northern species that rely on snow and sea ice as important winter habitats (Kausrud et al. 2008; Lunn et al. 2016). For example, rodents (Microtus spp., Lemmus spp., and Dicrostonyx spp.) rely on snow for shelter and insulation and seals rely on sea ice for breeding, so lower habitat quality due to altered snow characteristics and reduced sea ice may influence the abundance and spatial distribution of these species (Stirling and Smith 2004; Kausrud et al. 2008; Lunn 2016). Lowered rodent population density can have broad ecological consequences because rodents are important prey for many predators, such as foxes (Vulpes spp.), weasels (Mustela spp.), and owls (Bubo spp.) (Krebs 2011). The reproductive success of Arctic foxes is positively related to lemming density, with high juvenile mortality in low lemming years (Tannerfeldt and Angerbjörn 1998; McDonald et al. 2017; Samelius and Alisauskas 2017). In years of low lemming density, seals may be an important resource for foxes during winter (Roth 2002, 2003; Dudenhoeffer et al. 2021).
Populations of northern rodents historically have fluctuated in regular 3-5-year cycles, with peaks followed by a rapid decline (Elton 1924; Chitty and Elton 1937). Recently, rodents in northern Europe and North America have experienced damped population fluctuations, and a well-supported hypothesis explaining this phenomenon is a reduction in winter snow quality (Kausrud et al. 2008; Bilodeau et al. 2013c; Domine et al. 2018; Poirier et al. 2021). In northern environments, thick, soft, low-density snow provides a warm, stable, oxygen-rich subnivean microclimate and energetically efficient access to vegetation or other resources (Pruitt 1970, Maclean et al. 1974; Sanecki et al. 2006; Reid et al. 2011). This high-quality snow provides conditions necessary for rapid rodent population growth because rodents live and potentially breed beneath the snow in winter (Fauteux et al. 2015). Shallow, hard-packed snow unsuitable for rodent winter habitat often covers the primarily flat Arctic tundra, as thick, insulative snow drifts preferred by rodents accumulate on the leeward side of raised topography and vegetation; hence high-quality subnivean habitat is a limited winter resource (Pruitt 1970; Kershaw 2001; Pomeroy and Brun 2001). Snow quality characteristics, such as thickness, hardness, and density, are strongly influenced by weather conditions, such as wind, precipitation, and temperature. Annual weather patterns, therefore, can also provide insight into the conditions of subnivean space for rodents (Pruitt 1970; Callaghan et al. 2011). Heavy snowfall followed by a quick freeze-up in fall, relatively long warm winters, ambient temperature stability, and warm summers have also been positively related to high rodent density (Shelford 1943, Halpin and Bissonette 1987, Scott 1993, Reid and Krebs 1996, Aars and Ims 2002, Reiter and Andersen 2011, Bilodeau et al. 2013abc). Damped rodent population cycles have been attributed to climate change promoting greater temperature variation, which instigates ice formation and lowers snow insulative properties (Kausrud et al. 2008, Callaghan et al. 2011, Dushesne et al. 2011, Legagneux et al, 2012, Bilodeau et al. 2013c). Consequently, changes in weather and reduction in snow quality may further limit suitable rodent winter habitats and reduce population growth through lower winter survival and reproduction (Kausrud et al. 2008, Callaghan et al. 2011, Dushesne et al. 2011, Fauteux et al. 2015).
Survival of Arctic seals has also been threatened by changing climate patterns. Seals use subnivean birth lairs to provide protection for pups, and spring rain events that are atypical in the Arctic can increase the vulnerability of seal pups by causing subnivean birth lairs to collapse or flood. Destruction of birth lairs can lead to lower juvenile survival through greater vulnerability to hypothermia and predation (Stirling and Smith 2004). Reduction in seal survival can also reduce the abundance of their predators, such as polar bears (Ursus maritimus), which are blubber specialists whose diet is primarily seals (Stirling and McEwan 1975, Lunn et al. 2016). As polar bears often just consume blubber and leave the remainder of seal carcasses, foxes can scavenge abandoned seal carcasses (Stirling and McEwan 1975). Furthermore, seals are important alternative prey for foxes in the Arctic, as Smith (1976) estimated that 21–58% of newborn ringed seal (Pusa hispida) pups were preyed upon by Arctic foxes.
Although predator-prey interactions are well studied, the indirect impacts of climate on predator populations through prey availability are less researched. The objectives of our study were to determine population trends of Arctic fox in the southern Arctic, where effects of climate change may be particularly strong, and the environmental characteristics affecting fox populations. If climate change negatively impacts Arctic foxes, we predict a decrease in Arctic fox abundance over time, a negative relation with red fox abundance, and a positive relationship with weather and snow variables associated with higher rodent density and seal carrion availability. These variables include a shorter sea ice-free period, increased snow thickness and insulation, increased snow duration, less rain in fall and spring, less variation in seasonal temperatures, and warmer seasonal temperatures. Predators have a vital ecological role, thus understanding direct and indirect influences on Arctic fox populations will contribute to a broader understanding of the impact of changing climatic conditions on Arctic species.