The wild wolf is often shown in the media as a fierce, scary killer, so when a You Tube video appeared early this year casting the predator as more of a savior, lots of folks were delighted. Instead of being portrayed as the big, bad beast that kills livestock, competes with hunters for prey, and makes kids worry about Little Red Riding Hood, the wolf in Yellowstone National Park was being heralded as the Prince Charming of the Trophic Cascade, a Canid American Hero that had come to save the park.
“How Wolves Change Rivers,” a You Tube video on the subject, narrated in the plummy British voice of writer George Monbiot, has repeatedly turned up in the media and on the BBC, TED Blog, KARMA TUBE, GrrlScientist, and the list goes perpetually on.
It tells a charming story that (one) explains a bit of science most of us can understand and tend to like, (two) is badly needed cheerful news instead of war updates, and (three) would be nice if it were completely true. About once a week I get an email from someone who knows I’m involved with the International Wolf Center saying, “Wow, have you seen this. It blew me away.”
It’s a happy story that won’t die, but at least in part, should.
Last week the International Wolf Center presented an evening program in which three wolf biologists debunked big chunks of the story. The Center’s Wolf Curator Lori Schmidt, Founder Dave Mech and Research Wildlife Biologist Shannon Barber-Meyer laid out the most recent findings on wolves’ real, less dramatic role in Yellowstone.
In a recent article in International Wolf magazine, Mech, who has studied wolves for 55 years, explained that, “’Trophic’ refers to food; a trophic cascade is a set of reactions down through a food pyramid starting with an animal like the wolf at the top, elk in the middle and plants at the base. A Yellowstone trophic cascade, then, involves the changes in plants caused by changes in the elk population caused by actions of wolves.”
The media had picked up the trophic cascade story, reporting that since wolves were extirpated in Yellowstone, the growing elk population browsed on and nearly decimated the willows and other growth along riverbanks. The loss of vegetation, including aspen, the story goes, had left birds with reduced habitat and beavers with little to eat. Lacking beaver dams, the river cut more deeply and narrowed away from the roots of remaining willows.
And then the positive ending to that version of the story: After wolves were reintroduced in Yellowstone in 1995 and 1996, elk and coyote populations decreased. Elk were killed in large numbers or were frightened away from the rivers by wolves. Fewer elk meant healthier vegetation, which allowed the return of songbirds and beavers. As beavers changed the river habitat, the trophic cascade resulted in more insects, fish, otters and amphibians. Wolves killed coyotes, which compete with them for food. And since wolves reduced the coyote population, smaller prey like mice, ground squirrels and rabbits rebounded, as did smaller predators like foxes.
The question, according to Schmidt, Mech and Barber-Meyer, is whether the recently restored wolves actually wrought any cascading effects. Research that began surfacing in 2010 questioned whether just one species had that much impact.
For example, while the number of coyote packs in part of Yellowstone were reduced after wolf introduction, they have returned to pre-wolf numbers, although the packs may be smaller, one study said.
A slide in the presentation titled, “But...What about the Beaver, Wally?” quoted a scientific publication revealing, “the rapid re-occupation of the Northern Range with persistent beaver colonies, especially along Slough Creek, occurred because Tyers of the Gallatin National Forest released 129 beavers in drainages north of the park.”
In addition to wolves, other contributors to the decline in Yellowstone’s Northern Range elk herd could have their pictures on wanted posters: coyotes, cougars, black bear, grizzlies and human hunters, when elk migrate out of the park.
Further, it’s true that the height and number of willow and aspen trees have increased some, but researchers point to a new weather pattern that occurred at the same time wolves were returned to Yellowstone. Temperatures rose, and the growing season increased by about 27 days, Mech said.
Research that fueled the original media frenzy on trophic cascades can’t stand up to new evidence. Some researchers, the media and the public have jumped to conclusions that are not borne out today. It’s true that the return of the wolf correlated with changes in the ecosystems of Yellowstone, but correlation is not necessarily the same as causation.
Top carnivores like the wolf do play a role in changes in complex systems like the one in Yellowstone, but much new research has shown that they have less effect than once thought. The story of the wolf as savior of a beautiful ecosystem was a compelling one, but honestly, the wolf was only one player. It’s still a charmer to many, but its casting as the Prince Charming of the Yellowstone Trophic Cascade is, at best, uncertain.