Ecosystem drivers of an Arctic fox population at the western fringe of the Eurasian Arctic

Abstract

The distribution of traditional breeding dens on the Varanger Peninsula (70-71°N) in northernmost Fennoscandia indicates that this area once harboured a large Arctic fox population. Early 20th century naturalists regarded the coastal tundra of the Fennoscandian Low Arctic to be a stronghold for the species. At the start of our research in 2004, however, the local Arctic fox population was critically small and most neighbouring populations had been extirpated. Here, we synthesize the results of 11 years of research to highlight ecosystem drivers behind the critical state of the Arctic fox in Low-Arctic Fennoscandia. We identify two fundamental drivers: (1) an increasingly climate-driven irregularity of the lemming cycle and (2) a management-and climate-driven increase in the abundance of red fox that is subsidized by more ungulate carrion. Arctic fox reproductive success is low when lemmings are scarce (despite high vole abundance), while red foxes exclude Arctic foxes from high-quality breeding territories in summer and from marine and terrestrial carrion in winter. Red fox culling on Varanger Peninsula may have prevented the extirpation of the Arctic fox population. However, one decade after the onset of this management action the Arctic fox population has failed to increase either because the action has been insufficient or because demographic and environmental stochasticity has precluded a positive response. We discuss options for future research and management of the Arctic fox in the Fennoscandian Low Arctic.

Flexibility in a changing arctic food web: Can rough‐legged buzzards cope with changing small rodent communities?

“…In conclusion, we showed how the response of a moderately specialized predator to small rodent abundance changed with a possibly climate‐driven change in small rodent dynamics and community composition. Our results confirm previous findings that changes in small rodent dynamics will be detrimental for arctic predators (Ims et al, ; Schmidt et al, ), but at the same time, they suggest that some predators will be able to partially adapt to these changes by modified responses of demographic rates to resource abundance. In order to understand the consequences of climate‐driven ecosystem changes and predict future species distributions, a better understanding of trophic interactions and their plasticity is important.…”

“…Moreover, a similar positive selection of lemmings has been observed in northern Sweden, in a small rodent community composed of Norwegian lemmings, grey‐sided voles, and tundra voles ( Microtus oeconomus ). The key role lemmings play for arctic predators has also been demonstrated for other species such as arctic foxes or snowy owls in Fennoscandia (Ims et al, ). The preference of predators for lemmings may be related to their larger size providing more food per hunting effort, and possibly to the fact that they are easier to catch.…”

“…Changes from cyclic to noncyclic small rodent dynamics have been described as regime shifts, because they have profound influences on the functioning of the ecosystems where they occur (Ims et al, ). The disappearance of regular lemming peaks can have catastrophic consequences for specialist predators like snowy owls ( Bubo scandiaca ) in eastern Greenland (Schmidt et al, ) or arctic foxes ( Vulpes lagopus ) in northern Scandinavia (Ims et al, ), whereas more flexible generalists are less affected. Millon et al () investigated the functional response of demographic rates of tawny owls ( Strix aluco ) to fluctuating vole abundances before and after a dampening of vole cycles and documented a drastic reduction in breeding probability with changed prey dynamics.…”

Arctic greening and bird nest predation risk across tundra ecotones

“…Small rodents (voles and lemmings) had a distinct 4-year population cycle with strong interspecific and spatial synchrony across the study region 31,36,37 . In order to determine the phases of the rodent cycle during the 5-year study period we used data from the trapping program described in ref.…”

Foreword to Supplement 1: research on a polar species—the Arctic fox

“…Conservation of the Arctic fox can be challenging where humans strongly interfere with its habitat, such as in many parts of Fennoscandia. Ims et al (2017) show that in north-eastern Norway, irregular lemming peaks (the result of milder winters) and abundant red foxes (subsidized by carrion from increasingly plentiful ungulates) have caused the present critically small size of the Arctic fox population. They use this knowledge to discuss options for future research and management of the regional Arctic fox population.…”