Selecting the best stable isotope mixing model to estimate grizzly bear diets in the Greater Yellowstone Ecosystem

John B. Hopkins, Jake M. Ferguson, Daniel B. Tyers, Carolyn M. Kurle

Research output: Contribution to journalArticlepeer-review

14 Scopus citations

Abstract

Past research indicates that whitebark pine seeds are a critical food source for Threatened grizzly bears (Ursus arctos) in the Greater Yellowstone Ecosystem (GYE). In recent decades, whitebark pine forests have declined markedly due to pine beetle infestation, invasive blister rust, and landscape-level fires. To date, no study has reliably estimated the contribution of whitebark pine seeds to the diets of grizzlies through time. We used stable isotope ratios (expressed as C, N, and S values) measured in grizzly bear hair and their major food sources to estimate the diets of grizzlies sampled in Cooke City Basin, Montana. We found that stable isotope mixing models that included different combinations of stable isotope values for bears and their foods generated similar proportional dietary contributions. Estimates generated by our top model suggest that whitebark pine seeds (35-10%) and other plant foods (56-10%) were more important than meat (9-8%) to grizzly bears sampled in the study area. Stable isotope values measured in bear hair collected elsewhere in the GYE and North America support our conclusions about plant-based foraging. We recommend that researchers consider model selection when estimating the diets of animals using stable isotope mixing models. We also urge researchers to use the new statistical framework described here to estimate the dietary responses of grizzlies to declines in whitebark pine seeds and other important food sources through time in the GYE (e.g., cutthroat trout), as such information could be useful in predicting how the population will adapt to future environmental change.

Original languageEnglish
Article numbere0174903
JournalPLoS ONE
Volume12
Issue number5
DOIs
StatePublished - May 2017

Bibliographical note

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ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology (all)
  • Agricultural and Biological Sciences (all)
  • General

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