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Beavers have influence. By cutting down trees and damming streams, these rodents are changing the world around them, raising water levels and creating habitats for diverse plants, insects, fish and other animals. They are among the most famous ecosystem engineers in the world, a designation for species that have a huge impact on their environment. Wolves are also powerful. They are apex predators and their ability to hunt is reflected in the food chain. They have a direct effect on prey, which in turn can affect vegetation, other animals, and even how streams flow. What exactly happens when an apex predator meets an ecosystem engineer and eats him, asks The New York Times (NYT).
This question is also the basis of a study published in the journal Proceedings of the Royal Society B, which investigated how wolves affect beaver activity and thus forest composition in Voyageurs National Park in northern Minnesota.
When left to their own devices, the beavers of Voyageurs National Park are busy. Adults spend the night in the forest cutting down trees, which they then transport back to their colonies to feed and use in construction and repair. It is on these mining trails stretching from their homes that the greatest danger lurks.
The study found that wolves attack beavers that venture further from their homes, limiting the extent to which these rodents can cut down trees and reshape the landscape. Previous research has already shown that wolves also prevent the creation of wetlands by hunting beavers.
As these toothy engineers carry out their projects, the wolves are “in a sense giving them permission to do so,” said Thomas Gable, author of both studies.
In the spring and summer, wolves lurk in ambush on these trails and catch many feeding beavers. In 2018, Gable noticed that wolves seemed to be hunting more beavers on more distant routes, suggesting they could be limiting beavers and their activity, he said.
Based on that hunch, Gable and his colleagues spent several years going to places where GPS-tagged wolves had spent 20 minutes or more and conducting forensic searches looking for beaver pieces. They came up with data detailing hundreds of kills, attempted ambushes, and trail lengths where they took place. When they compared this data, they found that wolves were actually hunting beavers on roads that were further away from beaver homes.
According to Emily Fairfax, an ecohydrologist at the University of Minnesota who was not involved in the study, the work provides a “solid, solid” basis for the intuitive idea that beavers stay near water for safety reasons.
To say definitively that wolves, or even beavers, are shaping a certain amount of forest would require taking into account a wider range of actors because there are “all kinds of other influences” on forest dynamics, said Clive Jones, senior research fellow emeritus at the Cary Institute for Ecosystem Studies in Millbrook, New York. He was not involved in this study, but in the 1990s he introduced the concept of ecosystem engineers with his collaborators. He said the Voyageurs National Park article raised interesting possibilities and hoped it would “catalyze many more studies.”
“Beavers are amazing drivers of change. And wolves play another important role,” added Gable.