Spatial organization of reproductive Arctic foxes Alopex lagopus:: responses to changes in spatial and temporal availability of prey

1. Home range size, spatial organization and territoriality of reproductive Arctic foxes were studied during the summer. The influence of spatial distribution and availability of the main prey was investigated in order to evaluate whether the spatial organization of Arctic foxes was coherent with key predictions of the resource dispersion hypotheses (RDH). The RDH includes the spatial characteristics of resource abundance, while there is also growing attention to the importance of the temporal characteristics of resource abundance. Hence the role of temporal and spatio-temporal predictability of prey explaining carnivore spatial organization was also investigated in this study. 2. The study was conducted on Svalbard; a simple High-Arctic terrestrial ecosystem which allowed unique estimates of prey abundance. The main prey of the Arctic fox (Svalbard reindeer Rangifer tarandus platyrhynchus, seabirds Alcidae and Procellariidae and geese Anseridae) was surveyed systematically. These surveys revealed highly contrasting patterns in prey abundance within the terrestrial ecosystem. 3. Arctic fox summer home ranges varied in size (4-60 km(2)), as well as in overlap (17-76%). The diverse spatial organization covaried with spatial and temporal patterns in prey abundance. Small home ranges (10 +/- 5.6 km(2)) with large overlap (76 +/- 19.6%) were characteristic for coastal areas where prey was concentrated in small patches and predictable both in space and time. Medium home ranges (23 +/- 4.2 km(2)) and overlap (50 +/- 6.6%) occurred inland where prey was clumped in larger patches and less predictable. Large home ranges (52 +/- 8.4 km(2)) with little overlap (17 +/- 3.5%) occurred inland where prey was widely scattered and unpredictable. 4. Spatial dispersion and richness of prey resources explained most of the variation in Arctic fox spatial organization. The RDH framework could be used to explain the presence of relaxed territoriality found in this study. We suggest that the observed absence of more permanent social groups is due to the extremely severe winter conditions which force juvenile individuals to disperse from the natal area during the first winter. 5. Predictability of resources was an additional significant factor affecting both home-range size and overlap. Resource predictability captures the degree to which an animal can depend on its environment to offer suitable and secure living conditions over time. 6. This study emphasize the need to incorporate both spatial and temporal characteristics of resource distribution in order to fully understand the diversity of spatial arrangements among carnivores.