by RALPH MAUGHAN
A new study by Dr. Bill Ripple and his colleagues, “Trophic cascades from wolves to grizzly bears in Yellowstone” in the Journal of Animal Ecology suggests a second way the return of wolves has helped the Yellowstone grizzly bears.
Grizzlies have thrived in Yellowstone Park in recent years despite the destruction of the cutthroat trout fishery, and the dearth of most of the thought-to-be vital whitebark pine stands with their nutritious nuts. The reason wolves helped the bears was them taking down more elk than the grizzlies ever could. Some the wolf-killed elk were promptly stolen from the wolves by the bears. Now a second positive effect of wolves for bears is being explored by a scientific team from Oregon State and Washington State Universities.
The reduction of elk numbers by wolves and the creation of a “landscape of fear” for the remaining elk has kept the remaining elk moving. In their wake berries have begun to proliferate. Everyone knows bears love berries, but they are not very abundant in most of Yellowstone Park. One of the major reasons is browsing by deer, but even more by elk and by trampling from the bison herds. Wolves, of course, target elk primarily, but the less numerous deer too, and bison are harassed and sometimes killed by wolves.
The researchers found that the proportion of berries in grizzly bear scat in August (berry month) has almost doubled over the years since wolves were returned.
Outside the Park, where the super-abundant non-native grazing animal lives, Bos primigenius (cow), berries are reduced by their grazing and trampling. The report suggest retiring cattle allotments in the grizzly bear recovery zone next to Yellowstone. This will increase berry production.
Thinking about the suggestions of the study, I note that cattle and elk compete almost directly for forage. Estimates are 90% overlap between the food preferences to the two animals. So, cleaning out the cattle on the area’s public lands would also benefit elk — more grass and forbs.
This study’s preliminary conclusions are important because the grizzly bear is slated for delisting from the threatened species list in the Greater Yellowstone recovery area. The boundaries of what will be the “Primary Grizzly Bear Conservation” area are thought by many to be too small to support the recovery grizzly population — not enough food. The bears need to be allowed to range more widely to secure what they need to eat. However, if the land inside the primary grizzly bear conservation area was more productive of bear food, its relatively small size would be more adequate.