July 29, 2013
Reintroduction of Wolves To Yellowstone Aids Grizzly Bears
Brett Smith for redOrbit.com - Your Universe Online
Thanks to 'predator control' practices, wolves were eradicated from Yellowstone National Park in 1926. Their reintroduction in 1995 has shifted the balance of the regional ecosystem and provided an unexpected bonus for the park's grizzly bears.
According to a new study in Journal of Animal Ecology, the return of wolves to the park has reduced the elk population, subsequently allowing wild berries to flourish and nourish Yellowstone's bear population.
"Wild fruit is typically an important part of grizzly bear diet, especially in late summer when they are trying to gain weight as rapidly as possible before winter hibernation," said study co-author William Ripple, a forest ecosystem professor at Oregon State University. "Berries are one part of a diverse food source that aids bear survival and reproduction, and at certain times of the year can be more than half their diet in many places in North America."
Study researchers said the resurgence of the berries is still in the early stages, but the phenomenon could ultimately benefit birds and pollinating insects as well.
"Studies like this also point to the need for an ecologically effective number of wolves," said co-author Robert Beschta, Ripple's colleague at OSU. "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."
As the declining elk population allows for plant recovery in the park, and leads to improved health for the local grizzlies, the bears act as another control on the elk herds. While elk have been a key food for Yellowstone grizzly bears over the last 50 years, the higher percentage of berries in their diet, as indicated by scat samples, may help offset any loss ofÂ elk that may have disappeared via wolf predation in recent years.
Although more research is necessary to examine the developing relationships among bears, wolves, elk and plants in Yellowstone, there are historical precedents for the situation. By the early 1900s, grizzly bears had become all but extinct in the American southwest, but not before shifting their diets to livestock depredation due to the overgrazing of plant-based food. Black bears became extinct on Canada's Anticosti Island after introduced white-tailed deer ravaged the island's berry shrubs.
The study authors noted that Yellowstone's wild berries could also provide a buffer against the pressures of climate change on whitebark pine nuts, a bear favorite. Previous research has shown that the bears are severely impacted during years of low nut production.
In their report, the researchers also observed that the foraging activities of livestock adjacent to the park can impact the foraging activities of wild animals. The scientists recommended retiring livestock allotments near the park to reduce bear-livestock interactions and increase the regions overall food supply.
Officials are closely tracking the health of Yellowstone's wolf population. According to the National Park Service, 98 wolves in 10 packs were living in Yellowstone along with two loners in 2011.