When wolves were eradicated from Yellowstone in the early 20th Century, the elk population boomed, devastating berry-shrubs relied upon by bears.
Details are published in the Journal of Animal Ecology.
A team from Oregon and Washington links the reintroduction of predatory wolves with a fall 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.