Which of the following is the most likely cause for the change in coat color observed in the wild fox populations?

ARCTIC FOX (Alopex lagopus)

RANGE: Circumpolar Arctic regions of Europe, Asia, North America, Greenland and Iceland, and islands of the Arctic, North Atlantic and North Pacific oceans.

A TRUE ARCTIC DENIZEN. The Arctic fox inhabits two of the coldest places on the planet — the Arctic tundra and sea ice. Well adapted to its environment, the Arctic fox is shielded from sub-zero winter temperatures by its thick, white fur coat. To help it retain heat, the Arctic fox has a compact body shape with short legs and ears, and countercurrent heat exchange in the circulation of its paws to help maintain its body temperature while it walks on frozen ground. Foxes seek shelter in snow burrows during unusually cold weather, and can lower their metabolic rate during cold snaps and food shortages to retain heat. In summer, Arctic foxes become dark grey to brownish blue to blend into the tundra, and turn their attention to raising young. Fox pairs rear litters averaging six to seven pups in dens on the tundra, some of which have been used by foxes for several hundred years. Arctic foxes typically live three to six years in the wild but with luck can reach 10 years of age.

The Arctic fox specializes in eating tundra-dwelling rodents including lemmings and voles — so much so that fox population cycles often mirror those of their prey. When lemmings are plentiful, Arctic foxes tend to survive better and have large litters that lead to peaks in fox numbers. However, in years when lemmings are scarce, foxes are more vulnerable to starvation and resort to eating other foods from birds to fish to carrion. In lean years, the sea ice provides an important foraging ground offering food resources that can help foxes survive the winter. Foxes have been found to roam great distances over pack ice, often following polar bears to scavenge their seal kills. Some foxes are able to capture ringed seal pups in their snow dens on the sea ice as an extra food source.

POPULATIONS IN TROUBLE.  European Arctic fox populations in Sweden, Finland and Norway were decimated by hunting for their fur in the early 20th century and have failed to recover despite total protection since 1940. Numbering around only 150 foxes, European populations are threatened with extirpation. Although the Arctic fox in the rest of its range is still considered fairly abundant, Arctic foxes have been disappearing from the southern edge of the tundra around the globe. This northward retreat raises cause for concern over the fox’s future.  

HOW DOES CLIMATE CHANGE AFFECT THE ARCTIC FOX?

The Arctic fox faces a multitude of threats from climate change: its sea ice and tundra habitat are shrinking, its lemming prey are becoming less abundant in some areas, and it faces increased competition and displacement by the red fox which is moving northward as temperatures warm.

LOSS OF SEA ICE AND TUNDRA HABITAT.  Because sea-ice habitat provides important winter food resources for Arctic foxes, especially in low lemming years, the loss of sea-ice foraging grounds is likely to result in lower winter survival and reproductive success for Arctic foxes. [1, 2] Desperate foxes deprived of the sea ice may resort to searching for food in human settlements and industrial sites, which increases the potential for conflicts with humans and often ends in foxes being killed. As temperatures warm, shrubs and trees are also moving into the tundra, converting the Arctic fox’s lichen and moss-dominated habitat into shrublands and woodlands. [3] In the Alaskan tundra, dwarf birch, willow, and white spruce have increased markedly over the past 50 years.

LESS LEMMING PREY. Because Arctic foxes rely heavily on lemmings for food, climate change impacts on lemmings can have profound effects on foxes. During the winter, lemmings live in spaces under the snow that provide insulation from the cold, protection from predators, and access to plant foods. If snow conditions are good, lemmings prosper and can even get a head start in raising young. However, in Norway, scientists have found that rising temperatures and changing humidity in recent decades have created cycles of thawing and icing in winter that result in poor snow conditions for lemmings. [4] These poor snow conditions have dampened lemming population cycles, creating a new pattern where lemmings never reach peak numbers. Scientists believe that the absence of regularly occurring lemming peaks is likely responsible for the breeding failures and dramatic declines in Arctic foxes in Norway. [5] Future climate change is likely to dampen lemming population cycles across wider areas of the Arctic.

RED FOX COMPETITION. The Arctic fox has a fierce competitor [5] — the red fox — a dominant, larger-bodied fox that can kill or expel the Arctic fox in areas of overlap. Red foxes historically lived south of the Arctic fox’s tundra habitat. However, red foxes have been moving northward at the same time that Arctic foxes have been retreating from the southern edge of the tundra. [6] Climate change appears to be a leading factor driving the northward movement of the red fox. Warming is converting the tundra to shrublands, which are favored by the red fox. Warming-related reductions in lemming populations are also lowering lemming grazing pressure on the tundra, favoring the shrublands that encourage the northward invasion of red foxes. [7]

1. Roth, J. D. 2002. Temporal variability in arctic fox diet as reflected in stable-carbon isotopes: the importance of sea ice. Oecologia 133:70-77.

2. Pamperin, N. J., and E. H. Follmann. 2008. Sea ice use by arctic foxes in northern Alaska. Polar Biology 31:1421-1426.

3. Post, E., M. C. Forchhammer, M. S. Bret-Harte, T. V. Callaghan, T. R. Christense, B. Elberling, A. D. Fox, O. Gilg, D. S. Hik, T. T. Hoye, R. A. Ims, E. Jeppesen, D. R. Klein, J. Madsen, A. D. McGuire, S. Rysgaard, D. E. Schindler, I. Stirling, M. P. Tamstorf, N. J. C. Tyler, R. van der Wal, J. Welker, P. A. Wookey, N. M. Schmidt, and P. Aastrup. 2009. Ecological dynamics across the Arctic associated with recent climate change. Science 325:1355-1358.

4. Kausrud, K. L., A. Mysterud, H. Steen, J. O. Vik, E. Ostbye, B. Cazelles, E. Framstad, A. M. Eikeset, I. Mysterud, T. Solhoy, and N. C. Stenseth. 2008. Linking climate change to lemmings cycles. Nature 456:93-98.

5. Hendon, J.-A., B.-J. Bardsen, N. G. Yoccoz, and R. A. Ims. 2008. Impacts of differential prey dynamics on the potential recovery of endangered arctic fox populations. Journal of Applied Ecology 45:1086-1093.

6. Hersteinsson, P., and D. W. MacDonald. 1992. Interspecific competition and the geographical distribution of red and Arctic foxes Vulpes vulpes and Alopex lagopus. Oikos 64:505-515.

7. Killengreen, S. T., R. A. Ims, N. G. Yoccoz, K. A. Brathen, J.-A. Henden, and T. Schott. 2007. Structural characteristics of a low Arctic tundra ecosystem and the retreat of the Arctic fox. Biological Conservation 135:459-472.

What triggers the change in coat color of the Arctic fox?

Which of the following includes the most likely change in the coloration of the beetle population after pollution and a correct rationale for the change?

How are foxes affected by climate change?

How are Arctic foxes affected by humans?