Résumé
In the Arctic tundra, predators face recurrent periods of food scarcity
and often turn to ungulate carcasses as an alternative food source. As
important and localized resource patches, carrion promotes co-occurrence
of different individuals, and its use by predators is likely to be
affected by interspecific competition. We studied how interspecific
competition and resource availability impact winter use of carrion by
Arctic and red foxes in low Arctic Fennoscandia. We predicted that
presence of red foxes limits Arctic foxes’ use of carrion, and that
competition depends on the availability of other resources. We monitored
Arctic and red fox presence at supplied carrion using camera traps. From
2006 to 2021, between 16 and 20 cameras were active for two months in late
winter (288 camera-winters). Using a multi-species dynamic occupancy model
at a week-to-week scale, we evaluated use of carrion by foxes while
accounting for the presence of competitors, rodent availability and
supplemental feeding provided to Arctic foxes. Competition affected
carrion use by increasing both species’ probability to leave occupied
carcasses sites between consecutive weeks. This increase was similar for
the two species, suggesting symmetrical avoidance. Increased rodent
abundance was associated with a higher probability of colonizing carrion
sites for both species. For Arctic foxes, however, this increase was only
observed at carcasses unoccupied by red foxes, showing greater avoidance
when alternative preys are available. Supplementary feeding increased
Arctic foxes' carrion use, regardless of red fox presence. Contrary
to expectations, we did not find strong signs of asymmetric competition
for carrion in winter, which suggests that interactions for resources at a
short time scale are not necessarily aligned with interactions at the
scale of the population. In addition, we found that competition for
carcasses depends on the availability of other resources, suggesting that
interactions between predators depend on the ecological context.