DYNAMICS OF THE ARCTIC FOX POPULATION IN SWEDEN

Arctic fox populations fluctuate widely with the abundance of prey, i. e. lemmings and voles (Arvicolinae). We have investigated the patterns and mechanisms of these fluctuations in arctic fox numbers through de n inventories during 20 years (1974-1993) in Sweden. Time series analy ses confirmed a four-year cyclicity in both arctic fox numbers and lit ter size. However, the different geographical regions were not in sync hrony. The fox population in the southern parts of the distribution ra nge has shown regular peaks during the whole period, whereas those in the northern and middle parts of Sweden have declined since 1982. In t he northernmost county, also litter sizes have decreased. These differ ences coincided with an absence of vole and lemming peaks in the north . Experimental feeding confirmed that food availability had a direct i mpact on breeding success and litter size, thereby limiting the popula tion. We conclude that the total number of arctic foxes in Sweden in 1 994 is as low as 40-80 animals.