Comparison of concurrent plains and wood bison diets at Elk Island National Park

Abstract

Understanding ecological niche is critical to the management and conservation of any species or population. For herbivores, dietary niche is critical for understanding habitat suitability, carrying capacity, and population and community viability. In closely related species with similar morphologies, dietary niches can diverge depending on environmental and seasonal factors. Elk Island National Park in Alberta, Canada, contains populations of both American bison (Bison bison) subspecies—plains bison (B. b. bison) and wood bison (B. b. athabascae)—in similar but separate habitats located at the historical confluence of the subspecies' distributions. Using generalized additive models and nutritional geometry, we compared the subspecies' dietary niches in terms of content and quality continuously for one year (Dec 2020 – Nov 2021). Both subspecies consumed primarily graminoids during winter, spring, and fall and incorporated a variety of forbs and woody plants during summer. Plains bison diets contained more upland grasses and digestible organic matter in their diet and less wetland graminoids (e.g., sedges) throughout the year. We also found differing dietary niches between the subspecies during the spring and summer months. Our unique, continuous analysis of annual diet content and quality can deliver insight into the similarities and differences between subspecies' dietary niches that should help improve management decisions, such as better matching between source populations and release areas for future translocations.