Importance
Grizzly bears (Ursus arctos) are considered by many to be a symbol of the wilderness because they survive in remote, wild areas that have not been extensively developed by people. Grizzly bears once roamed throughout the west from the Arctic tundra in the north to arid Mexico in the south. Loss of habitat and extermination programs designed to protect cattle, sheep, and other livestock led to their demise throughout most of the United States by the early 20th century. Due to its remoteness and protections afforded by National Park status over much of the region, the Greater Yellowstone Area (GYA) became one of the last refuges for grizzly bears in the lower 48 states. In 1975, the U.S. Fish and Wildlife Service listed grizzly bears in the U.S. south of Canada as a Threatened Species, and designated a portion of the GYA as one of 6 recovery areas. Yellowstone and Grand Teton National Parks form the core of the GYA recovery area, providing a large area where grizzly bears and their habitat are well protected from human sources of mortality and development.
Status and Trends
The estimated GYA grizzly bear population increased from 136 bears occupying approximately 5 million acres in 1975 when they were listed as a Threatened Species, to 602 bears occupying approximately 14 million acres in 2010. During 2010 aerial and ground surveys, 51 different females with 101 cubs were recorded. Most GYA grizzly bears use habitat within the Recovery Zone, where priority is given to managing lands so as to maintain grizzly bear habitat and reduce human-caused bear mortalities. Grizzly bears have also reoccupied areas where they had been absent for decades and have now reoccupied areas outside of the Recovery Zone where they share land management priority with human uses.
Grizzly bears inside Yellowstone National Park are considered to be at ecological carrying capacity with cub production exceeding mortality on an annual basis, providing a source for emigration of subadults to areas outside of the park. Since 1997 (1997-2011), 398 grizzly cubs have been produced in Yellowstone Park, and only 15 bears have died from human causes (8 management removals & 7 road-kills).
In 1998, grizzly bears in the GYA met all of the recovery criteria required for delisting. In 2007 grizzly bears were removed from Threatened Species status. In September of 2009, a federal district judge overturned the delisting ruling and ordered grizzly bears placed back on the Threatened Species list. The judge ruled that: 1) the Conservation Strategy that guides management after delisting was unenforceable and non-binding on state and federal agencies, and 2) that the U.S. Fish and Wildlife Service (USFWS) did not adequately consider the impacts of the potential loss of whitebark pine nuts, a grizzly bear food source. The USFWS appealed the decision. In 2011, the Ninth Circuit Court of Appeals ruled in favor of the USFWS on the issue of the Conservation Strategy providing adequate regulatory mechanisms to conserve bears after delisting, but against the USFWS on the whitebark pine issue, resulting in the GYE grizzly bear population remaining on the Threatened Species list.
Discussion
Whitebark pine seeds are a preferred fall food for grizzly bears and have some influence on grizzly cub production, survival, and the number of grizzly bear-human conflicts. There is potential for a significant reduction of whitebark pine in the GYA due to the introduction of white pine blister rust an exotic organism, in combination with mortality caused by native mountain pine beetle and climate change which may facilitate more competition from other tree species and potentially increase wild fire intervals in whitebark pine habitat. Grizzly bears have evolved a life history including large home range sizes, highly flexible diet switching behavior, and an omnivore generalist diet designed to buffer them against the annual and seasonal vagaries of their foraging environment. Despite the current level of whitebark pine mortality, the GYE grizzly bear population continues to increase in numbers and expand in range. At present female grizzly bear survival remains above the level necessary to maintain population increase even in poor whitebark pine seed production years. Human factors more than environmental factors will determine how many grizzly bears persist into the future in the GYA. The best predictors of grizzly bear mortality on the landscape are human developments and the density of roads and homes, not the spatial distribution of whitebark pine trees
