Add Wolves, Subtract Elk = More Berries for Bears!

First, a little natural history background information.

(1938 park poster, via Wikimedia)

Yellowstone was declared as the first National Park In March 1872, signed into law by President Ulysses S. Grant, an act that created one of today’s most-visited U.S. parks.  Although a national park, poaching decimated the ungulate populations (e.g., elk, bison) and carnivores.  In 1883, the Secretary of the Interior banned hunting of most animals in National Parks, excluding larger carnivores and omnivores.

Unregulated hunting of ungulates in Yellowstone was largely curtailed by 1886.  However, increased pressure from neighboring ranchers and citizens resulted in the Grey Wolf (Canis lupus) being extirpated from Yellowstone.  The last official killing within the park occurred in 1926.

(Gray Wolf, Fish and Wildlife Service)

Fast forward to 1967.  Within the first year of the Endanger Species Preservation Act, the Gray Wolf classified as endangered.  Around this time, the importance of wolves as a predator was becoming more apparent.  Cultural views soon followed the scientific findings that Gray Wolves, an apex predator, play a significant role in shaping the communities in which they live.

(Bull Elk By Mongo, via Wikimedia Commons.)

1995.  After decades of absence, and 20 years of planning, wildlife biologists introduced 14 wolves to Yellowstone National Park.  Wolves were observed to feed primarily on elk (Cervus elaphus).  The Yellowstone Nation Park Gray Wolf populations seemed stable following another addition of 17 wolves in 1996.

Now on to the “neat news”…

Ripple et al. just published an article in the Journal of Animal Ecology examining the hypothesized tropic cascade resulting from the absence, and then reintroduction of Gray Wolves in Yellowstone. 

In a nutshell: 

(Grizzly bear, via Wikimedia)

The presence of wolves has indirectly caused in increase abundance of berries in the diet affected the of Grizzly bears (Ursus arctos) in Yellowstone National park, which in the result of reduced herbivory of and competition for berries by wolf’s preferred food, elk.

Without wolves, park populations of elk were, on average, 12 elk square kilometer, and Elk populations declined following wolf reintroduction, to approximately one elk per square kilometer.  Lower Elk population densities have resulted in increased woody plant recruitment, particularly berry-producing shrubs.  Ripple et al. (2013) demonstrate that this shift in plant community composition (Ripple and Beschta, 2012) also resulted in a shift in Grizzly Bear feeding behavior – an increase in berry consumption. 

Figure 6 (Ripple and Beschta, 2004) illustrating creek plant community composition in 1996 (left),
and the same location in 2002 (right), following wolf population establishment.  (Image via Lycographos)

Original article and other works cited:

Ripple, William J., Beschta, Robert L., Fortin, Jennifer K., Robbins, Charles T. 2013. Trophic cascades from wolves to grizzly bears in Yellowstone. Journal of Animal Ecology. DOI 10.1111/1365-2656.12123.

William J. Ripple and Robert L. Beschta. 2012. Beschta. Trophic cascades in Yellowstone: The first 15 years after wolf reintroduction. Biological Conservation. 145(1):205-213. http://dx.doi.org/10.1016/j.biocon.2011.11.005.

William J. Ripple and Robert L. Beschta. 2004. Wolves and the Ecology of Fear: Can Predation Risk Structure Ecosystems? BioScience. 54(8):755-766. DOI: 10.1641/0006-3568(2004)054[0755:WATEOF]2.0.CO;2

Background information sources:  Gray Wolf Endangered Species Profile (FWS); Yellowstone National Park webpage and pages therein; Yellowstone Wolf Project (Nat'l Park Service. 1996. YCR-NR-97-4).