Spatial variation in grizzly bear ( Ursus arctos ) dietary niche across British Columbia

Dietary niche variation can be a key driver of spatial variation in animals’ behaviour, population dynamics, and sensitivity to threats. Grizzly bears ( Ursus arctos Linnaeus, 1758) are a wide-ranging omnivorous mammal with enormous dietary flexibility. We used the stable isotope composition in over 2500 hair samples to estimate the proportion of vegetation, terrestrial meat, anadromous salmon (genus Oncorhynchus Suckley, 1861), and nonanadromous kokanee salmon ( Oncorhynchus nerka Walbaum, 1792) in the diet of over 1800 grizzly bears from across British Columbia. We then created fine-scale maps of grizzly bear diet for the province by using parametric generalized additive mixed effects models with spatial random fields. We found that grizzly bear's dietary niche in B.C. can be broadly categorized into either reliance on salmon or reliance on plant foods. Terrestrial meat sources and kokanee provided important supplements in certain regions. Available salmon biomass was the most important parameter in modelling dietary niche, while climate continentality was most important for modelling terrestrial meat. These results provide crucial knowledge to bear ecology and management that can be used at fine scales to consider the local impacts on bears or at broad scales to manage populations across ecosystems.