Genetics Prove Greater Yellowstone Grizzly Population Is Growing

The grizzly bear population in the Greater Yellowstone Ecosystem, which includes Yellowstone and Grand Teton national parks, is growing and not suffering from a loss of genetic diversity, according to a report from the Interagency Grizzly Bear Study Team.

The analysis shows that the bear population in the ecosystem has continued to grow since the 1980s, as well.

Results indicate that the effective population size of Yellowstone grizzly bears, or the number of individuals that contribute offspring to the next generation, has increased 4-fold over a 25-year period. This provides evidence that Yellowstone grizzly bears are approaching the effective size necessary for long-term genetic viability, the study said.

“The increase in effective size of the Yellowstone grizzly bear population over the past several decades, with no significant change in genetic diversity, supports evidence of population growth based on traditional surveys,” said Pauline Kamath, USGS ecologist and lead author of the study. “This is a key genetic indicator of a population’s ability to respond to future environmental change.”

They found estimates of effective population size increased from approximately 100 bears in the 1980s to 450 in the 2000s. These numbers are smaller than estimates of total population size because not all animals in the population breed. Although an isolated population, grizzly bear genetic diversity remained stable and inbreeding was relatively low, 0.2 percent, over the time period.

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