Yellowstone grizzly bears remain genetically isolated

By Kelsey Dayton
— September 2, 2014

In 2005 a grizzly bear from the Northern Continental Divide ecosystem was found dead southwest of Anaconda, Montana. Frank van Manen, team leader of the interagency grizzly bear study team, didn’t know the cause of death, but the sub-adult male was found about half way between the Northern Continental Divide Ecosystem — home of the Glacier National Park grizzlies — and the Greater Yellowstone Ecosystem. It was the closest attempt at the two populations mingling that biologists know of in recent history.

As wildlife managers consider removing Yellowstone grizzly bears from the endangered species list this year, the animals remain genetically isolated, a fact that worries some biologists while others say it isn’t an issue.

Genetic diversity helps animal populations thrive and also survive unforeseen challenges like disease or climate change, said Christine Wilcox, a biologist with the Natural Resources Defense Council. Linkage is one of the top concerns among conservations groups when it comes to survival of the Yellowstone grizzly, she said. The bear population might be healthy now, but the species could find itself in trouble in the future without more genetic diversity. Wilcox said that by the time a problem is detected, it will be too late to protect linkage areas, which could be lost to development, and it will be even harder for the populations to naturally connect.

Grizzlies used to occupy so much territory, including the space between the Northern Continental Divide and the Greater Yellowstone ecosystems, it was common for bear populations to mingle. Today the two populations are separated by about 150 miles. Bears have been known to travel 100 miles in a season, so they could potentially still meet, but it’s a dangerous journey.

“Right now it’s a gauntlet run,” Wilcox said. “Yes they can make it. But the chance of a conflict, which leads to mortality, is really high.”

That will likely only get worse when the bears are delisted and protections in the linkage zones disappear. Some separation between the populations is fine, but total isolation isn’t good for either population, Wilcox said.

The Yellowstone bear’s genetic diversity is considered “moderate,” van Manen said. There are populations, such as in coastal Alaska, that have much lower diversity than the Yellowstone bears, and those animals are still healthy and vigorous, he said.

There also hasn’t been a decline in genetic diversity in the Yellowstone population. The inner agency grizzly bear study team monitors the genetic diversity of the bear population using DNA collected each time biologists capture bears. That genetic information tells scientists the age of the animal, and also provides data on the overall genetic diversity of the population, van Manen said. The monitoring would show if an animal from another ecosystem traveled into the Yellowstone, which hasn’t yet happened, but van Manen said he isn’t worried.

“It’s always desirable to have genetic exchange among populations,” van Manen said. “That allows populations to have that genetic diversity that allows the population to adapt to new circumstances. However, if you ask me if it’s essential, or a big concern for the greater Yellowstone, my answer is ‘no.’ We don’t see anything in our data that shows that would create a concern.”

Genetic issues don’t manifest unless population numbers are really low. It’s rare for wildlife populations to cross that threshold where the animals start inbreeding and it causes survival issues, van Manen said. If the bears were delisted and there were signs of genetic diversity declining in the Yellowstone bears, there’s protocol built into the conservation strategy including transplanting bears from other populations if necessary.

Genetic changes can take a long time to detect and often by the time there are obvious changes, the population is in serious trouble, said Erin Edge, Rockies and Plains representative with Defenders of Wildlife.

“Long-term connectivity is really important for resiliency of the population and long-term genetic health,” she said.

It’s particularly important in the Yellowstone population which, with an estimated 741 bears, has less genetic diversity than the Northern Continental Divide bears, which has a population estimated at about 1,000 bears and also could be delisted soon.

How the bears might naturally meet is unknown.

“It’s still kind of a best guess as to where and how the bears will connect, and none of it will matter if they get into trouble along the way,” Wilcox said. “In the end the grizzly bears will tell us where and how they’ll move.”

As that happens it’s important to educate people about living in what is again becoming bear country, Edge said.

Bears in both populations are expanding their range beyond the core areas into places they haven’t habituated for decades. The best way to encourage genetic health of the populations is to allow the bears to mingle and that means bear mortalities need to be minimized in the linkage areas, Edge said. Much of the land between the two ecosystems is private land and people who own it aren’t used to seeing bears.

The important thing is working on preventing human-bear conflicts by educating people about securing their property and attractants, like garbage, bird feeders and pet food. People must also become familiar with resources and strategies such as electric fences to protect livestock and orchards, Edge said.

Delisting the bears removes protections that help ensure safety as the bears move into new areas, but connectivity is still possible in a delisting world, she said.

How delisting the Yellowstone bears from the endangered species list, expected to happen this year, will impact that expansion is unknown. “It’s hard to predict how the states will manage the bears,” said van Manen.

The further bears move away from the core area, the higher the mortality rates as they encounter more roads and unsuitable habitat. In Yellowstone the bears are expanding their range further south and east more so than moving northwest toward the Northern Continental Divide population. But van Manen said he believes that eventually some bears, likely from the larger Northern Continental Divide population, will move into new genetic territory.

“I wouldn’t be surprised if we see some genetic exchange within the next 10 years or so,” he said.

The study team and van Manen plan to present population and mortality numbers for the bears for the Greater Yellowstone Coordinating Committee of the Yellowstone Ecosystem Subcommittee at its next meeting of wildlife managers and agencies on October 28 in Bozeman, Montana. A decision on whether or not to delist grizzly bears is expected by the end of the year.

— “Peaks to Plains” is a blog focusing on Wyoming’s outdoors and communities. Kelsey Dayton is a freelancer and the editor of Outdoors Unlimited, the magazine of the Outdoor Writers Association of America. She has worked as a reporter for the Gillette News-Record, Jackson Hole News&Guide and the Casper Star Tribune. Contact Kelsey at kelsey.dayton@gmail.com. Follow her on twitter: @Kelsey_Dayton

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