by Hilary Bruegl
In the nineteenth century Arctic tundra of Finnmark, Norway, the Arctic fox population declined to near extinction and have been recovering minimally despite strict protection. Hamel et al. (2013) investigated potential factors involved in suppressing healthy recolonization of prior territories, including encroaching red fox populations and variation in prey availability. By baiting and periodically photographing the area, the authors found red foxes to be the most important influence on the Arctic fox population in northeast Norway. Not only are red foxes more comfortable in the warming temperatures of the tundra, but there has also been a significant reduction in fox hunting, allowing the red fox population to flourish. Rodent population fluctuations were first documented alongside fox populations as a limiting factor of population growth; however, they had fewer effects than either land cover changes or red fox infiltration.Hamel and colleagues used a camera-trap set to take photographs at ten-minute intervals. Frozen reindeer remains were used to bait the animals to the camera areas, which were located within various habitats and altitude levels. In the locations used as controls, no red foxes were removed. In an experiment to test a possible solution to low Arctic fox numbers, red foxes were removed from some camera-trap areas. These data were categorized into either presence or absence of either red or Arctic foxes, and then compared against habitat data including red fox culling, distance from road or coastal habitat, altitude, and prey abundance. Abundance of prey—specifically lemmings—was evaluated using data from a rodent monitoring program running in tandem with this experiment.
Arctic foxes were found only under very specific environmental conditions; the number Arctic foxes increased moderately with an increase in the number of lemmings and an increase in the distance of the camera trap from forest areas, but altitude was not a great determining factor of Arctic fox inhabitance. Distance from paved roads had almost two times the positive correlation with Arctic fox colonization than either lemming abundance, distance from forest, or altitude. The number of red foxes using an area, on the other hand, had a strong negative correlation with the number of Arctic foxes using an area. Arctic foxes were never found in an area in which three or more red foxes were sighted, and only recolonized an area from which red foxes were removed, but no Arctic foxes recolonized control areas in which no red foxes were culled or removed. Red foxes comprise the main mammalian competition for Arctic foxes; they hunt similar prey and can easily adapt to the warmer conditions that have begun to characterize Arctic fox habitat. Additionally, red foxes are larger on average than Arctic foxes, giving the species a distinct advantage and effectively deterring Arctic foxes from using areas occupied by red foxes but suitable in all other aspects.
The increase in Arctic fox sightings as distance from paved roads increases usually indicates a distance from human interference or habitat fragmentation as a result of physically sectioning off areas of migration with roads, but in this case, there is low human density in the study area. The roads in Finnmark, Norway are also generally located near the coast among forest habitats. Hamel et al. suggest that this strong correlation is a result of the combined factors of human interaction, habitat fragmentation, and dense forests.
There has been a gradual range expansion for red foxes as Arctic temperatures rise as a result of global warming. This northward trend allows for more red foxes to colonize and compete with Arctic foxes in their natural habitat. Red foxes, because they are larger and greater in number since the reduction of foxhunting, have a distinct advantage over the Arctic fox. Because of the red fox’s competitive advantage and range shifts, humans will have to actively intervene in culling efforts if the Arctic fox species is to survive.
Hamel, S., Killengreen, S. T., Henden, J. A., Yoccoz, N. G., Ims, R. A., 2013. Disentangling the importance of interspecific competition, food availability, and habitat in species occupancy: Recolonization of the endangered Fennoscandian Arctic fox. Biological Conservation 160, 114–120.