Unraveling Omnivory and Community Interactions Between Primary Producers and an Apex Predator

The effects of climate and plant phenological changes on herbivorous species are widely recognized, yet less research has focused on predatory species, even though vegetative components can account for large proportions of their diet. The historical focus on predation through the lens of simple interactions between obligate carnivores and their prey oversimplifies many species' roles within ecological communities and minimizes other, equally important community functions. We used a long-term, individual-based dataset on an omnivorous species, the brown bear (Ursus arctos), to identify long-term diet patterns and factors contributing to annual variation in diet. We used carbon and nitrogen stable isotopes measured in hair and Bayesian mixing models to determine annual diet among three demographic classes and then used linear mixed models to relate diet to indices of food availability. Variation in both carbon and nitrogen values were explained by bilberry (Vaccinium myrtillus) productivity. Additionally, even as the moose population increased over time, there was no increase in the proportion of moose in the diet. The variation in the proportion of moose in the diet slightly decreased throughout the study, while the proportion of bilberry became increasingly more variable. Our results highlight that even though vegetative diet components are typically considered less important to predator ecology, brown bear diet in Sweden responded to changes in berry availability, regardless of prey availability. It will be crucial to put more emphasis on the vegetative parts of diets as we predict how species and ecological communities respond to climate change because predators serve many more functions within their community besides predation alone.