Did wolves really 'change the rivers' of Yellowstone? The truth is more complicated.
When wolves returned to Yellowstone in 1995, elk numbers fell, willows recovered in places and beaver colonies multiplied. It became a famous story of a predator healing an ecosystem. Ecologists agree the wolves mattered, but say the park is far too complex for such a simple tale.
Yellowstone, created in 1872, offered wolves no protection. Government predator-control programmes killed them across the West, and the last wolves in the park, two pups, were killed by rangers in 1926. Without them, elk multiplied. Scientists visiting in 1929 and 1933 described the range as in deplorable condition, with aspen, cottonwood and willow heavily browsed. Rangers trapped and culled elk for decades, until hunters' complaints ended the culls in the late 1960s. Coyotes boomed too.
Attitudes shifted as ecologists such as Adolph Murie and Aldo Leopold argued for predators, and the Endangered Species Act of 1973 opened a legal path to reintroduction. In January 1995, 14 wolves captured in Alberta, Canada, were brought to the Lamar Valley and released that March; 17 more followed in 1996. Farm groups objected, arguing among other things that the Canadian wolves were the 'wrong' subspecies, a claim the park rejects.
The effects have been real. Each wolf kills about 22 elk a year, well above the 12 predicted, and the northern elk herd fell from about 16,800 to 8,300 between 1995 and 2004, though bears, human hunting, hard winters and drought also played a part. Wolves halved coyote numbers within two years, which appears to have helped foxes. Beaver colonies rose from one in 2001 to nine by 2011 as willows recovered along some streams, and ravens, eagles and bears feed on wolf kills.
But the popular idea that wolves 'saved' the park oversimplifies. Yellowstone is an open system with several top predators, including grizzlies, cougars and human hunters, and much of the northern range has not returned to its old 'beaver–willow' state. Without beaver dams, streams cut deeper and the water table dropped, leaving poor conditions for willows; one experiment found willows recovered only when elk were fenced out and artificial dams added. A 21-year analysis even concluded that the much-cited 'landscape of fear', elk avoiding wolves, played little role in local changes. The wolves started a cascade; they did not turn back the clock.
Source: Wikipedia — History of wolves in Yellowstone · Text summarised from Wikipedia (CC BY-SA 4.0)
