Body and diet composition of sympatric black and grizzly bears in the Greater Yellowstone Ecosystem

Journal of Wildlife Management
By: , and 

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Abstract

The Greater Yellowstone Ecosystem (GYE) has experienced changes in the distribution and availability of grizzly bear (Ursus arctos) food resources in recent decades. The decline of ungulates, fish, and whitebark pine seeds (Pinus albicaulis) has prompted questions regarding their ability to adapt. We examined body composition and diet of grizzly bears using bioelectrical impedance and stable isotopes to determine if 1) we can detect a change in diet quality associated with the decline in either ungulates or whitebark pine, and 2) the combined decline in ungulates, fish, and pine seeds resulted in a change in grizzly bear carrying capacity in the GYE. We contrasted body fat and mass in grizzly bears with a potential competitor, the American black bear (Ursus americanus), to address these questions. Grizzly bears assimilated more meat into their diet and were in better body condition than black bears throughout the study period, indicating the decline in ungulate resources did not affect grizzly bears more than black bears. We also found no difference in autumn fat levels in grizzly bears in years of good or poor pine seed production, and stable isotope analyses revealed this was primarily a function of switching to meat resources during poor seed-producing years. This dietary plasticity was consistent over the course of our study. We did not detect an overall downward trend in either body mass or the fraction of meat assimilated into the diet by grizzly bears over the past decade, but we did detect a downward trend in percent body fat in adult female grizzly bears after 2006. Whether this decline is an artifact of small sample size or due to the population reaching the ecological carrying capacity of the Yellowstone ecosystem warrants further investigation.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Body and diet composition of sympatric black and grizzly bears in the Greater Yellowstone Ecosystem
Series title Journal of Wildlife Management
DOI 10.1002/jwmg.633
Volume 78
Issue 1
Year Published 2013
Language English
Publisher John Wiley & Sons
Publisher location Hoboken, NJ
Contributing office(s) Northern Rocky Mountain Science Center
Description 11 p.
First page 68
Last page 78
Time Range Start 2000-01-01
Time Range End 2010-12-31
Country United States
State Idaho, Montana, Wyoming
Other Geospatial Grand Teton National Park, Yellowstone National Park
Online Only (Y/N) N
Additional Online Files (Y/N) N