Effects of resource availability and interspecific interactions on Arctic and red foxes' winter use of ungulate carrion in the Fennoscandian low-Arctic tundra

Abstract

In the Arctic tundra, predators face recurrent periods of food scarcity and often turnto ungulate carcasses as an alternative food source. As important and localized re-source patches, carrion promotes co-occurrence of different individuals, and its useby predators is likely to be affected by interspecific competition. We studied howinterspecific competition and resource availability impact winter use of carrion byArctic and red foxes in low Arctic Fennoscandia. We predicted that the presence ofred foxes limits Arctic foxes' use of carrion, and that competition depends on theavailability of other resources. We monitored Arctic and red fox presence at supplied carrion using camera traps. From 2006 to 2021, between 16 and 20 cameraswere active for 2 months in late winter (288 camera-winters). Using a multi-speciesdynamic occupancy model at a week-to-week scale, we evaluated the use of carrionby foxes while accounting for the presence of competitors, rodent availability, andsupplemental feeding provided to Arctic foxes. Competition affected carrion use byincreasing both species' probability to leave occupied carcasses between consecu-tive weeks. This increase was similar for the two species, suggesting symmetricalavoidance. Increased rodent abundance was associated with a higher probability ofcolonizing carrion sites for both species. For Arctic foxes, however, this increase wasonly observed at carcasses unoccupied by red foxes, showing greater avoidance whenalternative preys are available. Supplementary feeding increased Arctic foxes' carrionuse, regardless of red fox presence. Contrary to expectations, we did not find strongsigns of asymmetric competition for carrion in winter, which suggests that interac-tions for resources at a short time scale are not necessarily aligned with interactionsat the scale of the population. In addition, we found that competition for carcassesdepends on the availability of other resources, suggesting that interactions betweenpredators depend on the ecological context.