Implications of a high-energy and low-protein diet on the body composition, fitness, and competitive abilities of black (Ursus americanus) and grizzly (Ursus arctos) bears

Citation metadata

Author: B.N. McLellan
Date: June 2011
From: Canadian Journal of Zoology(Vol. 89, Issue 6)
Publisher: NRC Research Press
Document Type: Report
Length: 9,687 words

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Abstract :

Plants are not ideal foods for bears yet many populations are largely vegetarian. Implications of this diet on the body composition, fitness, and competiveness of black (Ursus americanus Pallas, 1780) and grizzly (Ursus arctos L., 1758) bears have had limited field investigation. The analysis of scats of grizzly and black bears from the Flathead valley, British Columbia, suggest seasonal dietary differences between species, but 85% of the summer diet of both species were fruits that are low in protein. Body composition measurements showed bears loose fat during spring, gained fat during summer, and grizzly bears were leaner than black bears. Individual black bears gained mass up to 2.7 times faster than theory predicted. Bears rapidly gained fat but lost lean tissues while feeding on fruit, suggesting that lean tissues were used to buffer seasonal protein shortages. Comparisons among populations of grizzly bears without access to salmon revealed the amount of meat in the diet was positively related with adult female mass but negatively related with bear density. Bears have the behavioural and phenotypic plasticity which enables populations that focus their foraging on plants to have small but fat females and live at higher densities than populations that focus more on obtaining terrestrial meat. Les plantes ne constituent pas les aliments ideals pour les ours, meme si plusieurs populations sont en grande partie vegetariennes. On a peu etudie en nature les consequences de ce regime alimentaire sur la composition corporelle, la fitness et la competitivite des ours noirs (Ursus americanus Pallas, 1780) et des grizzlis (Ursus arctos L., 1758). Les analyses des defecations de grizzlis et d'ours noirs de la vallee de la Flathead, Colombie-Britannique, indiquent des differences saisonnieres de regime entre les especes, mais 85 % du regime d'ete des deux especes consiste de fruits qui sont pauvres en proteines. Les mesures de composition corporelle montrent que les ours perdent de la graisse au printemps et reprennent de la graisse durant l'ete et que les grizzlis sont plus maigres que les ours noirs. Les ours noirs individuels reprennent de la graisse jusqu'a 2,7 fois plus rapidement que ne le predit la theorie. Les ours accumulent rapidement de la graisse, mais perdent des tissus maigres en se nourrissant de fruits, ce qui fait croire que les tissus maigres sont utilises pour contrer les carences saisonnieres en proteines. Des comparaisons faites entre des populations de grizzlis qui n'ont pas acces aux saumons montrent que la quantite de viande dans le regime est en relation positive avec la masse des femelles adultes, mais en relation negative avec la densite des ours. Les ours possedent une plasticite comportementale et phenotypique qui permet aux populations qui concentrent leur recherche de nourriture sur les plantes d'avoir des femelles petites mais grasses et de vivre jusqu des densites plus elevees que les populations qui cherchent plutot jusqu obtenir de la viande d'origine terrestre. [Traduit par la Redaction]

Source Citation

Source Citation
McLellan, B.N. "Implications of a high-energy and low-protein diet on the body composition, fitness, and competitive abilities of black (Ursus americanus) and grizzly (Ursus arctos) bears." Canadian Journal of Zoology, vol. 89, no. 6, June 2011, pp. 546+. Accessed 17 Oct. 2021.
  

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