Wolves, Grizzlies, Elk and Berries - an unexpected set of dependencies

I just got through reading the Science Daily version [1] of a journal article, Trophic cascades from wolves to grizzly bears in Yellowstone.[2] The article describes how an unexpected relationship has been discovered between the populations of wolves, elk and grizzly bears through berries. Turns out without wolves around the elk suffered little predation - except for human hunting - and their expanding numbers fed on berries, reducing their availability to the grizzly bear. However, the grizzly really needed that late summer/early fall crop of berries to get them ready for winter, so fewer berries meant fewer grizzlies. Although grizzlies are omnivores and did take their share of elk, this was not enough to sustain their numbers. So with the re-introduction of wolves, the population of elk was naturally reduced, which led to more berries being available, which led to greater numbers of grizzlies surviving their winters. So, very simplistically, the relationship could be represented by a series of statements:

Wolves /\ => Elk \/

Elk \/ => Berries /\

Berries /\ => Grizzlies /\

Therefore,

Wolves /\ => Grizzlies /\

What is really interesting to me is that there has tended to be a certain hysteria that has taken over discussions in the US about re-introducing wolves into local wilderness over the last 40 years or so. The hysteria seems to be driven by anectdotal "evidence" of how wolves are responsible for widespread livestock losses, reductions of game animals such as elk, or deaths of humans and/or their pets. Although the wolf does indeed feed upon both wild prey and domesticated animals, the wolf seems to have been portrayed as an evil and vicious creature in fables and myths as a result of the view centered on our reliance on the sheep, cows and pigs we've raised for sustenance. Even so, the wolf needs to calculate any preference for domesticated livestock over wild prey against fear of humans. If there is a shortage of wild prey (often called "game animals" in the US), then the wolves' hunger will overcome that fear. In Eurasia where there is little wild prey available, wolves are much more likely to attack domesticated livestock than in the US where there are substantial numbers of animals for the wolves to feed on [3][4].


[1] Of bears and berries: Return of wolves aids grizzly bears in Yellowstone
[2] William J. Ripple, Robert L. Beschta, Jennifer K. Fortin, Charles T. Robbins. Trophic cascades from wolves to grizzly bears in Yellowstone. Journal of Animal Ecology, 2013; DOI: 10.1111/1365-2656.12123
[3] http://en.wikipedia.org/wiki/Gray_wolf#Relationships_with_humans
[4] Mech, L. David; Boitani, Luigi (2003). Wolves: Behaviour, Ecology and Conservation. University of Chicago Press. ISBN 0-226-51696-2.