Wednesday, July 31, 2013

Report: Wolves help Yellowstone grizzly bear survival

Reduction in elk numbers leaves more berry bushes


By EXPRESS STAFF

    A new study suggests that the return of wolves to Yellowstone National Park is beginning to bring back a key part of the diet of grizzly bears that has been missing for much of the past century—berries that help bears put on fat before going into hibernation.
    The report was published today by scientists from Oregon State University and Washington State University in the Journal of Animal Ecology. The researchers found that the level of berries consumed by Yellowstone grizzlies is significantly higher now that shrubs are starting to recover from overbrowsing by elk herds. The berry bushes also produce flowers of value to pollinators such as butterflies, insects and hummingbirds, as well as food for other mammals and birds.
    The report said berries may be sufficiently important to grizzly bear diet and health that they could be considered in deciding whether to change the “threatened” status of grizzly bears under the Endangered Species Act.
    “Studies like this also point to the need for an ecologically effective number of wolves,” said co-author Robert Beschta, an OSU professor emeritus. “As we learn more about the cascading effects they have on ecosystems, the issue may be more than having just enough individual wolves so they can survive as a species. In some situations, we may wish to consider the numbers necessary to help control overbrowsing, allow tree and shrub recovery, and restore ecosystem health.”
    The study found that the percentage of fruit in grizzly bear scat in recent years almost doubled during August.
    There is precedent for high levels of ungulate foraging causing problems for grizzly bears. Before going extinct in the American Southwest by the early 1900s, grizzly bear diets shifted toward livestock depredation, the report noted, because of lack of plant-based food caused by livestock overgrazing.
    Increases in berry production in Yellowstone may also provide a buffer against other ecosystem shifts, the researchers noted; whitebark pine nut production, a favored bear food, may be facing pressure from climate change. Grizzly bear survival declined during years of low nut production.
    Livestock grazing in grizzly bear habitat adjacent to the national park, and bison foraging in the park, likely also contribute to high foraging pressure on shrubs and forbs, the report said. In addition to eliminating wolf-livestock conflicts, retiring livestock allotments in the grizzly bear recovery zone adjacent to Yellowstone could benefit bears through increases in plant foods.




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