Figure 2

The non-linear relationship between dietary protein content and the energy required to maintain body mass (maintenance cost) for brown bears fed diets varying in dietary protein content (data points) in comparison to the dietary protein levels selected and consumed by wild and zoo polar bears. Low and high protein diets are associated with high maintenance energy costs. The dietary protein content selected by wild polar bears feeding on marine mammals as indicated by the solid vertical line, and the dietary protein content selected by zoo polar bears in feeding studies with ad libitum access to lean meat and lard as indicated by the dashed vertical line were within the range associated with minimization of maintenance energy costs. Brown bear diets ranged from 100% fruit (3% protein) to 100% salmon (61% protein) or 100% white-tailed deer^9,10,11,24. Reference²⁴ did not report meat protein content, so the protein content of white-tailed deer meat was determined from Ref.²⁵. Digestible dry matter was converted to kcal using dry matter digestibility of deer for brown bears from Ref.²⁶.