"This is direct evidence for the dramatic beneficial effect of conservation policies enacted through legislation such as the U.S. Endangered Species Act," say David Mattson of the USGS Colorado Plateau Field Station at Northern Arizona University in Flagstaff and Troy Merrill of LTB Consulting in Moscow, Idaho, in the August issue of Conservation Biology.
To help find the best way to protect grizzly bears, Mattson and Merrill determined factors that correlated with the species' survival since 1850. The researchers considered a variety of factors including the availability of foods such as salmon, bison and whitebark pine (which have large seeds that the bears eat); habitat type and size; the presence of livestock and agriculture; and the density of people.
Mattson and Merrill found three factors that strongly correlate with the survival of grizzly bears today: the presence of whitebark pines, large ranges and low human density. One thing these factors have in common is that they help keep grizzlies away from people, who have been the primary cause of the species' decline. For instance, the bears' survival in areas with whitebark pines is presumably due to the fact these trees only grow at high elevations and so are far away from most places where people live.
Grizzly bear populations have also been more likely to survive in contiguous ranges that are greater than 7,700-square miles. In 1970 the only populations with more than 200 grizzlies were in the Yellowstone and Northern Continental Divide recovery areas, and both of these areas exceed 7,700-square miles. While the Bitterroot and North Cascades recovery areas also approach this size, they have few if any grizzly bears. The other two recovery areas are smaller than 2,700-square miles.
Finally, grizzly bears have been more likely to survive in areas with few people. Before 1970, grizzly populations were far more likely to survive where the density of people was less than 1.3 per square mile. Today, however, grizzlies are persisting at much higher human densities (about 5 and 8 people per square mile for Yellowstone and the Northern Continental Divide recovery areas, respectively).
Mattson and Merrill attribute the grizzly bears' current survival at higher human densities to legal protections such as the 1973 ESA. "Our results show that changes in human attitudes and behavior have been critical to the survival of grizzly bears from 1970 to the present," say the researchers.
Most of the grizzly recovery areas are smaller or have higher human densities than optimum. "These results argue for continued stringent protection of grizzly bears in the Cabinet-Yaak, Selkirk and North Cascade ranges and high-priority restoration of bears in the Bitterroot Range," say the researchers.
The Yellowstone grizzly population is doing best and there have been proposals to remove its ESA protections. However, grizzlies there depend on whitebark pines, which are threatened by a non-native disease (white pine blister rust) that has largely eradicated them north and west of the Yellowstone ecosystem. "Such vulnerability…argues for the inadvisability of removing any legal protections for this [grizzly bear] population," say Mattson and Merrill.
FOR MORE INFORMATION:
USGS Forest and Rangeland Ecosystem Science Center
http://fresc.usgs.gov/fffacts/grizzly/GrizzlyBear.html
For PDFs of papers, contact Robin Meadows: robin@nasw.org
[NOTE: I will be on vacation 7/27-31]
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Journal
Conservation Biology