Yes, Wolves Change Rivers. And So Much More.

So yes: wolves do change rivers. But it is unlikely that they are the only force changing them. Instead, they are part of a complex web of ecological goodness, making the habitat healthier for all.

The changes at Yellowstone aren’t just an elegant recipe for ecological balance

Christianity Today / Behemoth | Issue 31

It wasn’t a surprise when the Yellowstone Wolf Project received a mortality signal from the radio collar of 925M, the alpha male of the Lamar Canyon pack. And it wasn’t happy news.

But then again, it wasn’t exactly bad news.

“It was a very impressive thing,” longtime wolf researcher Rick McIntyre told tourists several weeks later. “He died a hero. He sacrificed his life and saved his entire family.”

925M, known to local and internet fans as “Big Gray,” had apparently been training his pups near Slough Creek when the family encountered the Prospect Peak pack. Rather than run away from the dozen or so rivals, 925M ran straight toward them, then past them, drawing them away from his pack.

“He was a big, strong guy. He was a fast guy. But he couldn’t outrun 12 wolves,” McIntyre said.

But the long-term good news behind 925M’s death was not that it had been seemingly heroic. It’s that he died from a wolf attack, rather than a hunter’s gun.

Yellowstone National Park, the first National Park in the world, is home to a myriad of species as well as to pristine Rocky Mountain wilderness. The park straddles Wyoming, Idaho, and Montana and became the first National Park for good reason: its natural beauty draws over three million visitors annually, from every corner of the globe.

The hot springs and geysers of Yellowstone were among the first places that researchers discovered single-celled microorganisms known as Archaea; they flourish in its hot, sulfuric pools. The park not only harbors extremophiles, it is a home for many iconic American species, from bald eagles to buffalo. The alpine landscape is dotted with broadleaf aspen trees, which anchor the rivers and keep soil from eroding into them. While the animals are not as plentiful as they were in the 1800s, massive herds of elk and buffalo famously roam and graze.

A century ago, wolves were not charismatic attractions for visitors to the park. They were a threat to the park’s attractions. “Gray wolves are increasing and have become a decided menace to the herds of elk, deer, mountain sheep, and antelope,” warns the 1915 superintendent’s annual report. “Several were killed in the park last winter, and an effort will be made the coming winter to capture or kill them.”

The efforts were wildly successful. An October 1926 photo shows two pups sitting atop a bison carcass, ears flat against their heads, as trappers close in. They would be the last known lupine residents of the park until 1995.

The eradication was disastrous. Combined with habitat loss for other top predators and increased grazing lands, the removal of wolves caused the elk population in the area to skyrocket. More elk roaming meant more elk eating, which hurt tree health throughout the park. Willows were hit especially hard, and their disappearance meant few building materials for the park’s beavers. The near disappearance of beavers, along with the soil erosion caused by fewer adult trees, significantly hurt streams, rivers, and floodplains.

You may have already heard all this, and that reintroducing wolves in 1995 started setting everything right again. The brief video How Wolves Change Rivers has more than 20 million YouTube views. George Monbiot, who narrated that video, described the process again in a popular TED Talk. It was a National Geographic cover story in 2010. There have been BBC documentaries, New York Times articles, and features in nearly every popular science journal.

And indeed it’s truly good news. The wolves altered elk behavior and moved them out of fertile valleys and into more sheltered areas, which allowed the willow and aspen trees along the rivers to grow taller. Fewer elk (and more skittish ones among the remaining population) increased the number of berries, which has been good for bears. It has meant more food for rabbits and mice, which has meant more hawks and eagles. More beavers have been able to eat the healthier trees, and their dams provide habitats for many animals. The dams and the trees’ deeper roots have made Yellowstone’s rivers healthier and swifter.

Ecologists call this kind of large-scale change a trophic cascade. Scientists appreciate it because it may be able to predict the impact of a single species on the health of the whole. But nothing about Yellowstone’s wolves is simple, politically or scientifically.

Two decades later, bringing wolves to the park remains as controversial as ever with local ranchers and hunters. And while researchers agree that wolves have significantly changed Yellowstone, there’s debate on how much other factors are at work too. Wolves aren’t the only thing that’s changed the park since 1995. Droughts have affected the rivers, trees, and animal life. Yellowstone has become more popular, leading to more development in the area. Bears seem to have developed more of a taste for elk. And while top-down trophic cascades are more intuitive (add a predator at the top, and you affect their prey, which affects their food, which affects their food…), ecologists are taking a closer look at “bottom-up” trophic cascades and how plants shape ecosystems. Some recent efforts are examining herbivores and trophic cascades that move from the center out. To summarize a room full of journal articles: Each player has a unique and important role in the health of its ecosystem. So yes, when an apex predator like the wolf is taken away, the whole ecosystem suffers. But the same was true two hundred years ago when beavers were decimated by trapping. Losing any one species hurts the whole. To update Paul’s “many parts, yet one body” metaphor in 1 Corinthians 12, the bison cannot say to the beaver, “I have no need of you.”

Occasionally in science, there are clear causal pathways. We know, for example, what wolves hunt and we can calculate how many elk are in the park. While some scientific questions are cut and dry, most are nuanced. In ecology, there are thousands of species in a given habitat, all exerting force on each other. Additionally, outside forces play a role, be they habitat destruction, highway placement, or pollution. So yes: wolves do change rivers. But it is unlikely that they are the only force changing them. Instead, they are part of a complex web of ecological goodness, making the habitat healthier for all.

The more we learn about science, the more complicated things become and the more difficult it is to draw neat conclusions. But would we have it any other way? We can only see so much from one vantage point. When we view the ecology of Yellowstone looking only for the effect of wolves, we get a majestic picture, but it is incomplete. This does not in any way discount the importance of wolves; without them the ecosystem gets sicker. But when we begin and end our analysis with them, we fail to appreciate the larger tale happening.

I love the simple, elegant story that wolves change rivers. But in the larger, more complex tale, I am reminded of the wildness of our planet. In biology, things tend to defy simple explanation. We humans sit, scratching our heads in amused befuddlement at the glory around us, while all the time God is in his heaven, knowing all that goes on in our world.

Joanna Daigle is a graduate student studying biochemistry at the University of Saskatchewan. Her previous article for The Behemoth, “Big Eaters,” examined macrophages. Ted Olsen is editor of The Behemoth.