Diet and Macronutrient Optimization in Wild Ursids: A Comparison of Grizzly Bears with Sympatric and Allopatric Black Bears

• Published in: PloS one Vol. 11; no. 5; p. e0153702
• Main Authors: Costello, Cecily M, Cain, Steven L, Pils, Shannon, Frattaroli, Leslie, Haroldson, Mark A, van Manen, Frank T
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 18.05.2016; Public Library of Science (PLoS)
• Subjects: Analysis; Animal behavior; Animal Nutritional Physiological Phenomena; Animals; Biology and Life Sciences; Body fat; Body mass; Body size; Buffalo; Carbohydrates; Carnivores; Demographic aspects; Diet; Ecology and Environmental Sciences; Ecosystems; Energy; Energy consumption; Energy intake; Feeding Behavior; Female; Food; Food and nutrition; Food availability; Food habits; Food intake; Food plants; Food selection; Geography; Geology; Grizzly bear; Grizzly bears; High protein diet; Insects; Lipids; Low protein diet; Male; Medicine and Health Sciences; Moose; National parks; Nutrient deficiency; Nutrition research; Optimization; Parks & recreation areas; Physiological aspects; Predictions; Proteins; Studies; Sympatric populations; Ursidae; Ursus americanus; Ursus arctos; Vertebrates; Wyoming; United States; Montana; Grand Teton; United States > US; Wyoming
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0153702

When fed ad libitum, ursids can maximize mass gain by selecting mixed diets wherein protein provides 17 ± 4% of digestible energy, relative to carbohydrates or lipids. In the wild, this ability is likely constrained by seasonal food availability, limits of intake rate as body size increases, and competition. By visiting locations of 37 individuals during 274 bear-days, we documented foods consumed by grizzly (Ursus arctos) and black bears (Ursus americanus) in Grand Teton National Park during 2004-2006. Based on published nutritional data, we estimated foods and macronutrients as percentages of daily energy intake. Using principal components and cluster analyses, we identified 14 daily diet types. Only 4 diets, accounting for 21% of days, provided protein levels within the optimal range. Nine diets (75% of days) led to over-consumption of protein, and 1 diet (3% of days) led to under-consumption. Highest protein levels were associated with animal matter (i.e., insects, vertebrates), which accounted for 46-47% of daily energy for both species. As predicted: 1) daily diets dominated by high-energy vertebrates were positively associated with grizzly bears and mean percent protein intake was positively associated with body mass; 2) diets dominated by low-protein fruits were positively associated with smaller-bodied black bears; and 3) mean protein was highest during spring, when high-energy plant foods were scarce, however it was also higher than optimal during summer and fall. Contrary to our prediction: 4) allopatric black bears did not exhibit food selection for high-energy foods similar to grizzly bears. Although optimal gain of body mass was typically constrained, bears usually opted for the energetically superior trade-off of consuming high-energy, high-protein foods. Given protein digestion efficiency similar to obligate carnivores, this choice likely supported mass gain, consistent with studies showing monthly increases in percent body fat among bears in this region.