Use of isotopic sulfur to determine whitebark pine consumption by Yellowstone bears: a reassessment

Wildlife Society Bulletin
U.S. Fish and Wildlife Service
By: , and 

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Abstract

Use of naturally occurring stable isotopes to estimate assimilated diet of bears is one of the single greatest breakthroughs in nutritional ecology during the past 20 years. Previous research in the Greater Yellowstone Ecosystem (GYE), USA, established a positive relationship between the stable isotope of sulfur (δ34S) and consumption of whitebark pine (Pinus albicaulis) seeds. That work combined a limited sample of hair, blood clots, and serum. Here we use a much larger sample to reassess those findings. We contrasted δ34S values in spring hair and serum with abundance of seeds of whitebark pine in samples collected from grizzly (Ursus arctos) and American black bears (U. americanus) in the GYE during 2000–2010. Although we found a positive relationship between δ34S values in spring hair and pine seed abundance for grizzly bears, the coefficients of determination were small (R2 ≤ 0.097); we failed to find a similar relationship with black bears. Values of δ34S in spring hair were larger in black bears and δ34S values in serum of grizzly bears were lowest in September and October, a time when we expect δ34S to peak if whitebark pine seeds were the sole source of high δ34S. The relationship between δ34S in bear tissue and the consumption of whitebark pine seeds, as originally reported, may not be as clean a method as proposed. Data we present here suggest other foods have high values of δ34S, and there is spatial heterogeneity affecting the δ34S values in whitebark pine, which must be addressed.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Use of isotopic sulfur to determine whitebark pine consumption by Yellowstone bears: a reassessment
Series title Wildlife Society Bulletin
Volume 38
Issue 3
Year Published 2014
Language English
Publisher The Wildlife Society
Publisher location Bethesda, MD
Contributing office(s) Northern Rocky Mountain Science Center
Description 7 p.
First page 664
Last page 670
Country United States
Other Geospatial Yellowstone National Park
Online Only (Y/N) N
Additional Online Files (Y/N) N