Wolves killing beavers changes wetlands environment, University of Minnesota study says

Humans are not the only apex predator to dramatically change its environment, University of Minnesota researchers claim in a recently published study.

Wolves observed in UMN's Voyageurs Wolf Project and Voyageurs National Park affected ecosystems by killing the beavers instrumental in creating those ecosystems, according to the Nov. 13 Science Advances research article.

The study offers an example in nature in which two species do not act symbiotically, the researchers suggest.

"If beavers are the natural ecosystem 'engineers,' creating wetlands across the circumpolar boreal ecosystem, then wolves can be thought of as a factor that directly influences such engineering by altering site-specific beaver construction that, in turn, influences the spatial and temporal distribution of wetlands," the study said.

Thomas D. Gable, who studies animal behavior, conservation and biodiversity, and population ecology at UMN, led the Voyageurs Wolf Project.

Other UMN researchers in the study included Sean M. Johnson-Bice, Austin T. Homkes, Steve K. Windels and Joseph K. Bump.

Gray wolves have long been recognized as "a premier example of how predators can transform ecosystems through trophic cascades," the study abstract said. "However, whether wolves change ecosystems as drastically as previously suggested has been increasingly questioned."

The study demonstrates how wolves killing beavers will "alter wetland creation and recolonization," the abstract said.

"By studying beaver pond creation and recolonization patterns coupled with wolf predation on beavers, we determined that 84% of newly created and recolonized beaver ponds remained occupied until the fall, whereas 0% of newly created and recolonized ponds remained active after a wolf killed the dispersing beaver that colonized that pond," the abstract said. "By affecting where and when beavers engineer ecosystems, wolves alter all of the ecological processes (e.g., water storage, nutrient cycling, and forest succession) that occur due to beaver-created impoundments. Our study demonstrates how predators have an outsized effect on ecosystems when they kill ecosystem engineers."

The study began in 2015 after a wolf was documented killing a beaver in a newly created pond, according to a research brief.

“Within days of the wolf killing the beaver, the dam failed because there was no beaver left to maintain it," Homkes, a Voyageurs Wolf Project field biologist, said in the brief. "The wolf appeared to have prevented the beaver from turning this forested area into a pond. This initial observation was fascinating and we realized we needed to figure out how wolves were connected to wetland creation in the Greater Voyageurs Ecosystem."

The pond not been recolonized by another beaver since this event, according to the brief.

After approximately five years of intensive fieldwork, researchers estimated that observed wolves "altered" roughly 88 beaver-created ponds each year and storage of more than 51 million gallons of water during that period in the Greater Voyageurs Ecosystem, the research brief said.

"How large predators impact ecosystems has been a matter of interest among scientists and the public for decades," Gable said.  "Because wolves are the apex predators in northern Minnesota and beavers are ecosystem engineers, we knew there was potential for wolves to affect ecosystems by killing beavers."