Abstract
Several large carnivore populations are recovering former ranges, and it is important to understand interspecific interactions between overlapping species. In Scandinavia, recent research has reported that brown bear presence influences gray wolf habitat selection and kill rates. Here, we characterized the temporal use of a common prey resource by sympatric wolves and bears and described individual and seasonal variation in their direct and/or indirect interactions. Most bear–wolf interactions were indirect, via bear scavenging of wolf kills. Bears used >50% of wolf kills, whereas we did not record any wolf visit at bear kills. Adult and subadult bears visited wolf kills, but female bears with cubs of the year, the most vulnerable age class to conspecifics and other predators, did not. Wolf and bear kill rates peaked in early summer, when both targeted neonate moose calves, which coincided with a reduction in bear scavenging rate. Some bears were highly predatory and some did not kill any calf. Individual and age-class variation (in bear predation and scavenging patterns) and seasonality (in bear scavenging patterns and main prey availability of both wolves and bears) could mediate coexistence of these apex predators. Similar processes likely occur in other ecosystems with varying carnivore assemblages.
Highlights
During the last two centuries, large carnivores have suffered drastic population declines, range contractions, and habitat fragmentation [1]
The only direct interaction that we could confirm occurred in 2012 at a yearling moose carcass killed by wolves in late March
There was likely another direct interaction in late June 2014, but the incomplete success of wolf GPS locations that day prevented confirmation. Both bear and wolf locations overlapped on the remains of a neonate moose, which had presumably been killed by the bear, based on sign found at the spot
Summary
During the last two centuries, large carnivores have suffered drastic population declines, range contractions, and habitat fragmentation [1]. Individual and seasonal variation in predation and scavenging rates may help understand the patterns of wolf habitat selection and kill rates in relation to brown bear presence reported earlier. We characterized the temporal use of a common prey resource by sympatric wolves and bears in Sweden, describing individual and seasonal variation in wolf–bear interactions. The latter can be direct, if individual wolves and bears meet at the same time, or indirect, if they use the same place or resource, but not simultaneously, which can provide evidence of exploitation competition, e.g., via scavenging. Describing individual variation and seasonal trends in kill and scavenger rates of competing carnivores can reveal underlying mechanisms behind the observed effects of bears on wolf habitat selection and kill rates at higher spatial and temporal scales. Our study contributes empirical data to document the role of individual variation and seasonality as drivers of interspecific interactions between apex predators via predation rates and scavenging, which in turn can reflect on predator-prey interactions
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