Wolves Help Grizzly Bears Get Berries
Since the reintroduction of wolves into Yellowstone National Park, the percentage of berry waste in bear poo has nearly doubled. Continue reading →
The discovery shows just how tightly woven ecosystems are, and how the domino effect can both hurt and benefit members.
The situation began to unfold back in the early 1900s, when officials had the short-sighted idea of moving wolves out of Yellowstone. It was called "predator control." By the 1970's, scientists found no evidence of a wolf population in Yellowstone, a verdant place that had previously been home to wolves for ages.
In October 1991, Congress provided funds to the U.S. Fish & Wildlife Service to start wolf restoration efforts at Yellowstone. (A central Idaho restoration was also funded then.)
The new study, published in the Journal of Animal Ecology, examined how the re-introduction of wolves is affecting other wildlife in the park.
Lead author William Ripple, an Oregon State University professor in the Department of Forest Ecosystems and Society, and his team found that, during the period with few or no wolves, elk herds expanded and over-browsed berry bushes. This was bad news for grizzly bears.
"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," Ripple said in a press release. "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."
Now, however, with wolves hunting elk again, there are more berries. Yellowstone is berry central for bears, with numerous types that they love: serviceberry, chokecherry, buffaloberry, twinberry, huckleberry and others. Since the reintroduction of wolves, the percentage of berry waste in bear poo has nearly doubled.
"Studies like this also point to the need for an ecologically effective number of wolves," co-author Robert Beschta, an OSU professor emeritus, said. "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 over-browsing, allow tree and shrub recovery, and restore ecosystem health."
The new plethora of berries is additionally producing flowers of value to pollinators such as butterflies, insects and hummingbirds. Birds are eating the berries, as are other animals, both small and large.
Since berries help bears put on fat before going into hibernation, it's then predicted that grizzly bear populations will strengthen, adding a second avenue of control on elk and other wild ungulates, especially on newborns in the springtime.
Achieving the right balance is important, though. Elks are critical to the ecosystem as well, so if their populations drop too much, more problems will surface. Taking a cue from history, however, park officials should probably let nature handle such matters on its own.
(Image: Yellowstone National Park)