Scientists debunk myth that Yellowstone wolves changed entire ecosystem, flow of rivers

Michael Kuhne

For centuries, the wolf has inspired long-standing myths and legends across the world. In recent years, viral videos online have spun new tales about the wolf, attributing immense ecological changes to the canine, including a cascade of effects powerful enough to alter the flow of rivers in Yellowstone National Park. 

While wolves are crucial predators in the Yellowstone food web, the story of a wolf-driven "trophic cascade" promoted in a popular online video is far from the complex reality of the park's ecosystem.

According to the video, which has nearly 40 million views, the re-introduction of wolves to the park helped reduce the elk population, in turn allowing the heavily browsed willows to grow taller.

As the willows grew, they provided the beaver with a source of food, which resulted in more dams and changed the flow of the park's rivers. 

"It's a really romantic story," Utah State University ecologist Dan McNulty said. "It's a story about a world that doesn't really exist."

The gray wolf was once a prominent predator across the North American continent and was found in the Yellowstone area when the park was established in 1872. By the mid-1900s, wolves in the park, and across the country, were nearly eliminated from the contiguous United States by humans.

In the early 1970s, no evidence of the animal could be found in Yellowstone, save an occasional report of a lone wolf roaming the countryside, according to the National Park Service.

Colorado State University's Natural Resource Ecology Laboratory professor Tom Hobbs said there is no dispute among scientists that removing the wolf from Yellowstone had vast ecological impacts on the park, but there is a "disagreement on what happens when you put it back."
"It's a lovely story, and I would love this to be true, but it isn't," Hobbs said. "[The video] is demonstratively false."

Hobbs, who uses the video to open many of his seminars, has written several research papers regarding Yellowstone's willows. His research indicates that wolves have had very little impact on willow growth since their 1995 reintroduction. 

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