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

Area of Science:

• Ecology and evolutionary biology
• Animal behavior and foraging ecology
• Wildlife ecology and conservation

Background:

• Understanding how organisms obtain energy is crucial for ecology, but simplified theoretical models can limit ecological insights.
• Brown bears (Ursus arctos), as a widely distributed, polyphagous species, offer a valuable case study for examining ecological theories.
• Disparate theoretical frameworks can lead to differing conclusions about ecological communities and species interactions.

Purpose of the Study:

• To illustrate how different ecological foraging theories can influence conclusions about brown bear diets and ecological roles.
• To estimate the dietary proportions of key food items for brown bears in Sweden using stable isotope analysis.
• To compare empirical dietary data with predictions derived from three prominent foraging hypotheses.

Main Methods:

• Stable isotope measurements (δ13C, δ15N) were conducted on brown bear hair samples from individually monitored bears in Sweden.
• Bayesian mixing models were employed to estimate the proportional contribution of ants, moose, and berry species to the bears' diets.
• Three distinct foraging hypotheses (optimal foraging, maximizing fitness, macronutrient balance) were developed and their predictions compared to empirical data.

Main Results:

• Brown bear diets primarily consisted of bilberries (50%-55%), lingonberries (22%-30%), and crowberries (8%-15%), with smaller proportions of ants (5%-8%) and moose (3%-4%).
• Empirical dietary protein content was lower in dry matter than predicted by maximizing fitness and macronutrient balancing models.
• While diets most closely aligned with optimal foraging theory predictions, no single hypothesis fully explained the observed foraging patterns.

Conclusions:

• Simplified ecological models may not fully capture the complex foraging strategies of polyphagous species like brown bears.
• Optimal foraging theory provides a reasonable, but incomplete, framework for understanding brown bear dietary choices in this region.
• Broadening and refining ecological models based on diverse foraging theories is essential for novel discoveries about species' roles in ecosystems.