The return of wolves to Yellowstone National Park in Wyoming, may be leading to an improvement in the diet of grizzly bears, a study suggests, published in the Journal of Animal Ecology.
When wolves were eradicated from Yellowstone in the early 20th Century, the elk population boomed, devastating berry-shrubs relied upon by bears. A team from Oregon and Washington links the reintroduction of predatory wolves with a decline in over-browsing by elk.
There is a consequent recovery in the availability of late-summer berries, the favoured pre-hibernation food of the grizzly bear. The study indicates that the number of berries measured in bear droppings has doubled as elk numbers have decreased, following the wolves’ return in the 1990s. The complex interactions of the Yellowstone ecosystem were revealed in data measured before and after the reintroduction of wolves.
David Mattson, a US Geological Survey (USGS) wildlife biologist, commented previously on Yellowstone: “It’s a complex system and grizzly bears are a kind of consummate connector of all of the species in that system.”
The study shows that berry shrubs have increased since elk populations declined, and as shrubs recover from over-browsing the fruit consumption of bears has increased.
William Ripple, lead author, commented: “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”.
“Elk browsing reducing berry production is well known in Europe as well,” said Atle Mysterud, an ecologist from the University of Oslo.
“The study shows that new patches of berries have formed after the wolves were reintroduced. It is clear that berry production is very important for bears.”
“This is an interesting paper and it is important that we understand the consequences of wolf recovery”, Dr Middleton added.
The latest results demonstrate that acknowledging the many inter-relationships between species and environments in these systems is key to understanding that complexity.