“Whitebark pine trees have declined due to an introduced fungal disease called blister rust, and, more recently, to increased infestation by the mountain pine beetle, which is exacerbated by climate change,” said study coauthor Carolyn Kurle, an assistant professor at UC San Diego’s Division of Biological Sciences. “Such declines further highlight the need to monitor diets of grizzlies as the environment continues to change.”
Once ubiquitous in western North America, whitebark pine trees have declined in recent decades and are now listed as endangered by the International Union for Conservation of Nature. Warming temperatures have led to shorter and milder winters, increasing beetle infestations and further threatening whitebark pine mortality.
Other potential food sources for grizzlies such as trout, deer and elk have also declined in the region.
Lead author Jack Hopkins, a former postdoctoral researcher in Kurle’s lab at UC San Diego and currently an assistant professor at Unity College, and his team measured stable isotopes found in bear hair and related their abundances to those found in their foods.
“Stable isotope analysis is a powerful ecological tool for reconstructing the diets of animals,” said Hopkins. “Instead of investigating the diets of animals based on what’s eliminated (feces), we estimate the importance of major food sources to animals based on what’s assimilated into their tissues. Using stable isotope analysis to conduct a retrospective diet analysis can shed light on how animals, such as Yellowstone grizzlies, have responded to changes in food availability on the landscape.”
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