Beavers are what biologists like Thomas Gable, who is based at the University of Minnesota, call ecosystem engineers. That’s because the hefty, flat-tailed rodents have a penchant for felling trees and damming streams, creating beaver ponds that dramatically alter the local habitat and, in aggregate, the entire ecosystem.
Within Voyageurs, this concept is especially true. Ponds and wetlands created by beavers are a huge part of the landscape, covering roughly 13 percent of the park’s land in 2019, according to new research published this week in the journal Science Advances.
So when a wolf kills a beaver, especially one that isn’t part of a colony, the effect on the surrounding environment ripples out. Without the furry engineer around to repair the structure of the dam, it swiftly breaks down and the pond dissipates, reports Christina Larson for the Associated Press (AP).
After first observing the phenomenon in 2015, the researchers decided to investigate the impacts of wolves preying on beavers by tracking 32 wolves via satellite collars from 2015 to 2019. The researchers kept an eye on what the wolves were up to, noting when one of the canines spent a bit more time lingering at a given location—a sign that it likely made a kill. By hiking into these locations, Gable and his colleagues were able to discern what the wolves had eaten, according to Science.
Beavers were definitely on the menu, but falling victim to the wolves didn’t appear to be depressing the beavers’ overall population in Voyageurs. However, Gable and his co-authors did notice a pattern: the wolves were mostly eating what the researchers call dispersing beavers—individuals that have left their colonies and struck out on their own to conquer new territory.
After four years of field research, Gable and his collaborators found that when a wolf kills one of these dispersing beavers it takes more than a year for another beaver to reoccupy the site. In this way, the wolves’ taste for beaver influences the locations of the rodents’ dams and the resulting ponds, since the abandoned dams quickly fall apart.
“Looking at it over time, you start to see how interconnected wolves are to wetland creation,” Gable tells Science.
During the study, wolf kills disrupted 88 beaver ponds, enough to sequester an estimated 51 million gallons of water across the Greater Voyager Ecosystem, roughly 700 square miles of forest that includes the national park, reports Jonna Lorenz for United Press International.
“Beavers are so central to the way these boreal forests look that anything that affects beaver distribution is going to have a cascading effect,” Rolf Peterson, an ecologist at Michigan Technological University who was not involved in the new study, tells AP.
The role of predators in shaping the ecosystems they inhabit has been an active and much-debated area of research in the realm of ecology. Past research concerning the reintroduction of wolves to Yellowstone National Park suggested that the predators’ impact on elk distribution within the park reduced the intensity of grazing along streams, and stabilized eroding banks as a consequence. But, as Goldfarb writes in Science, these conclusions have been hotly debated and subsequent research has painted a more complex picture of how interactions between wildlife can transform ecosystems.
But this latest work in Voyageurs National Park appears to at least present a more straightforward mechanism for the wolves’ influence on the ecosystem.
In a statement, Joseph Bump, study co-author and a biologist at the University of Minnesota, says their new research “hints at the possibility that wolves might have a longer-term impact on wetland creation and generate habitat patchiness that supports many other species across the landscape, but we need to study this mechanism further.”