Food limitation and social regulation in a red fox population

This study evaluates a conceptual model on functional and numerical response to short‐term fluctuating vole populations of a red fox ( Vulpes vulpes L.) population in south‐central Sweden. The model assumes that this particular population is located in between socially regulated stable populations to the south and direct food‐limited populations to the north. The model predicts: (1) food availability as the primary factor for limiting fox numbers, causing reduced rates of reproduction and survival during years of low vole densities, and (2) density‐dependent regulation during years of increasing and high vole densities resulting in increased group sizes within territories of fixed dimensions. During 1973–1980 data were obtained from 1216 fox scats, 874 fox carcasses, 63 tagged foxes, nine radio‐collared females and from yearly den counts in an area of 130 km 2 , Eight predictions of the model were tested. These concerned the occurrence of small rodents in fox diet, fluctuations in the density of foxes, variations in the number of fox litters, the effect on reproduction of providing supplemental food during January–May, the proportion of vixens bearing a litter different years, dispersal of young males relative to that of young females throughout the vole cycle, and variations in mortality rates of young males and females. All tests were in favour of the conceptual model, and contradictory to alternative models.