Measuring the impact of a changing climate on threatened Yellowstone grizzly bears

May 11, 2017
Grizzly bears photographed with a remote camera at a hair-snaring station in Cooke City Basin, Montana. Credit: Remote camera, U.S. Forest Service

Climate change is altering the environment in Yellowstone National Park and its surrounding region and scientists at the University of California San Diego and Unity College are studying its impacts on the diets of threatened grizzly bears.

A study published May 11 in PLOS ONE focused on modeling the diets of in Cooke City Basin, Montana, part of an area designated as the Greater Yellowstone Ecosystem (GYE). Evidence from the team's research in the study area and a recent habitat-selection study by Montana State University indicates that grizzly bears continue to forage for whitebark pine seeds as a diet staple. Diet proportions derived from isotopic data, however, suggest that some bears could be responding to reductions in whitebark trees by consuming more plants and berries.

Once ubiquitous in western North America, the slow-growing 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 and ungulates have also declined in the region.

"Whitebark pine trees have declined due to an introduced fungal disease called blister rust, and, more recently, to increased infestation by the , 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."

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 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 to conduct a retrospective analyses can shed light on how animals, such as Yellowstone grizzlies, have responded to changes in food availability on the landscape."

Previous research has shown that whitebark pine seeds—often cashed in large middens by red squirrels—are raided by grizzlies in the fall, fueling reproduction and ensuring the survival of grizzlies in the region. A main reason threatened grizzly bears have remained protected for decades is because it has not been clear how declines in whitebark pine trees, and thus the seeds they provide bears, will impact population trends over the long term.

Because their inferences are limited to a small area in the region and a small number of bears, the researchers recommend a large-scale study and urge others to use their new modeling framework to investigate the diets of other species of concern.

"Such analyses could be used to monitor grizzly bear recovery efforts and inform other wildlife conservation and management programs worldwide," Hopkins added.

Explore further: Grizzly bears still need protecting, US court rules

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ForFreeMinds
1 / 5 (1) May 12, 2017
Interesting article considering there's evidence the grizzly population in Yellowstone is growing:
https://www.natio...-growing

Is all the grant money going to global warming/climate change based research? I'd respect this research a lot more if they didn't use the power of government to take money from people to fund it. Taking money from people for the benefit of politically favored scientists and politicians is an immoral endeavor.
zz5555
5 / 5 (1) May 12, 2017
Of course, adding hunting restrictions on grizzlies will tend to increase the population of, you know, grizzlies. And, since the article isn't about the current population trends of grizzlies, ForFreeMinds comment has as much relevancy as saying, "but the sun is yellow".

However, it doesn't take a genius to figure out that decreasing the availability of grizzlies' food will make it hard for the grizzly to continue to recover. But, then, no one's likely to confuse ForFreeMinds' political whining for genius - or even competence.
GlennGraham
not rated yet May 12, 2017
The old link that ForFreeMinds points to carefully avoids using population numbers. According to the Interagency Grizzly Bear Committee, there were 757 grizzly's in the Greater Yellowstone Ecosystem in 2014, 717 in 2015 and 690 in 2016. So - not growing. The government / US Fish and WildLife Service is pushing hard to delist the grizzly's under strong pressure from the states, the ranchers, and the extraction industries. News that climate change is negatively affecting the bear population is not welcome for those that want to delist them.

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