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How absolute biomass intake can alter nutrient profile interpretation in free-ranging species: The case of protein intake in brown bears

De Cuyper, Annelies1; Janssens, Geert1; Clauss, Marcus2

Published Apr 10, 2025 on Dryad. https://doi.org/10.5061/dryad.bnzs7h4nk

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Apr 10, 2025 version files 26.33 KB

Abstract

If an animal eats a large amount of a diet of a low content of a macronutrient, it can still ingest a considerable amount of that macronutrient. Various animals have been shown to balance nutrient content with intake in this way. We use the brown bear (Ursus arctos) as a model species, given their recent classification as ‘low protein omnivores’, to show how taking biomass intake into account can affect macronutrient intake interpretation. We 1) calculated absolute protein intake from published results of self-selection diet studies with bears in captivity and 2) modelled absolute protein intake of Swedish brown bears in autumn while binging on a berry diet of low protein concentrations. In feeding experiments in captivity, the self-selected macronutrient composition of brown bear diets are characterized by protein percentages (both on a dry matter and metabolizable energy basis) that appear low when compared to diets of carnivores. However, when taking into account absolute food intake and expressing this as daily protein intake per metabolic body mass (33-117 g/kg0.75/d), protein intake was considerably higher than established minimum requirements for domestic dogs and cats (2.6-3.8 g/kg0.75/d) – carnivores one would not consider ‘low protein specialists’. Our hypothetical berry model yielded a protein intake of 3.2-9.7 g/kg0.75/d, which is lower than the outcomes from the self-selection trials but still comparable to established requirements of domestic dogs and cats. Instead of perceiving bears as low-protein consumers, it might be more accurate to perceive them as temporary hyperphagia specialists for which low protein concentrations are necessary to avoid dramatically overshooting protein requirements. Including absolute food intake in diet determination offers important nuances in result interpretation. When coining labels to categorize animals, it may be advisable to not only consider nutrient concentrations but also absolute intake.