Department of Biological Sciences, University of Alberta Edmonton, Alberta, Canada
Background/Question/Methods
Nutrition dictates many animal-environment interactions by influencing body condition, foraging, and reproduction. Many studies have investigated the nutrient limitations of wildlife (e.g., protein vs. energy limitation) to inform population modelling, carrying capacities, and habitat management, but often the ultimate limiting nutrient cannot be isolated and identified. For example, despite extensive studies, the nutritional drivers of snowshoe hare (Lepus americanus) feeding choices and fitness costs of these choices remain unknown. Nutritional geometry, a nutritional ecology framework that measures animal responses to multiple nutrients simultaneously, provides a theoretical construct for how hares, and other wild herbivores, balance multiple nutrients to define their optimal diet. Here, under the nutritional geometry framework, we conducted single-choice feeding trials during February and March of 2022 in the Kluane region of the Yukon, Canada. We measured snowshoe hare feeding rates, weight change, and protein digestion in response to four formulated diets of differing protein:fibre ratios (0.088 [diet A]; 0.22 [diet B]; 0.36 [diet C]; 0.50 [diet D]).
Results/Conclusions
We conducted 4 3-day feeding trials, one per diet, on eight hares (n = 32). On average (± standard deviation), hares ate 89.84 ± 14.24 g/kg of diets and lost 0.45 ± 0.94% body mass per day of feeding trial across all diets. Hares had the lowest consumption rates on the diet with the second highest protein content (diet C; 74.73 ± 13.20 g/kg/day) and the highest consumption rates when on the diet with the lowest protein content (diet A; 105.71 ± 11.0 g/kg/day). Despite the low consumption rates of diet C, hares performed the best on this diet (-0.26 ± 0.90 % body mass/day). Despite the highest consumption rates, hares still lost the most weight on diet A (1.48 ± 0.78 % body mass/day), which had similar protein:fibre ratios to lower quality winter browse. We infer that snowshoe hares practice compensatory feeding on high-fibre foods, likely to achieve a minimum protein intake. However, the highest protein content of diet D, did not provide the greatest fitness benefit.
