Testing foraging optimization models in brown bears: Time for a paradigm shift in nutritional ecology?

• Published in: Ecology
• Main Authors: Mikkelsen, Ashlee J., Hobson, Keith A., Sergiel, Agnieszka, Hertel, Anne G., Selva, Nuria, Zedrosser, Andreas
• Other Authors: Robert Bosch Stiftung
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2023
• Subjects: Ecology, Evolution, Behavior and Systematics; Alces alces; Empetrum nigrum; Ursus arctos
• Online Access: http://dx.doi.org/10.1002/ecy.4228; https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.1002/ecy.4228

Abstract How organisms obtain energy to survive and reproduce is fundamental to ecology, yet researchers use theoretical concepts represented by simplified models to estimate diet and predict community interactions. Such simplistic models can sometimes limit our understanding of ecological principles. We used a polyphagous species with a wide distribution, the brown bear ( Ursus arctos ), to illustrate how disparate theoretical frameworks in ecology can affect conclusions regarding ecological communities. We used stable isotope measurements (δ 13 C, δ 15 N) from hairs of individually monitored bears in Sweden and Bayesian mixing models to estimate dietary proportions of ants, moose, and three berry species to compare with other brown bear populations. We also developed three hypotheses based on predominant foraging literature, and then compared predicted diets to field estimates. Our three models assumed (1) bears forage to optimize caloric efficiency (optimum foraging model), predicting bears predominately eat berries (~70% of diet) and opportunistically feed on moose ( Alces alces ) and ants ( Formica spp. and Camponotus spp; ~15% each); (2) bears maximize meat intake (maximizing fitness model), predicting a diet of 35%–50% moose, followed by ants (~30%), and berries (~15%); (3) bears forage to optimize macronutrient balance (macronutrient model), predicting a diet of ~22% (dry weight) or 17% metabolizable energy from proteins, with the rest made up of carbohydrates and lipids (~49% and 29% dry matter or 53% and 30% metabolizable energy, respectively). Bears primarily consumed bilberries ( Vaccinium myrtillus 50%–55%), followed by lingonberries ( V. vitis‐idaea 22%–30%), crowberries ( Empetrum nigrum 8%–15%), ants (5%–8%), and moose (3%–4%). Dry matter dietary protein was lower than predicted by the maximizing fitness model and the macronutrient balancing model, but protein made up a larger proportion of the metabolizable energy than predicted. While diets most closely resembled predictions from optimal ...