Wolves affect wetland ecosystems by killing beavers leaving their colonies to create new ponds.

 

Beavers are some of the world's most prolific ecosystem engineers, creating, maintaining and radically altering wetlands almost everywhere they live. But what, if anything, might control this engineering by beavers and influence the formation of North America's wetlands?

In a paper to be published Friday in the journal Science Advances, researchers with the University of Minnesota's Voyageurs Wolf Project and Voyageurs National Park observed and demonstrated that wolves affect wetland ecosystems by killing beavers leaving their colonies to create new ponds.

Beavers are important ecosystem engineers that create wetlands around the world, storing water and creating habitat for numerous other species. This study documents that wolves alter wetland creation when they kill beavers that have left home and created their own dams and ponds.

Juvenile beavers disperse alone and often create new ponds or fix up and recolonize existing, old ponds. By studying pond creation and recolonization patterns along with wolf predation on beavers, project biologists and co-authors Tom Gable and Austin Homkes found that 84% of newly-created and recolonized beaver ponds remained occupied by beavers for more than one year. But when a wolf kills the beaver that settles in a pond, no such ponds remain active.

This relationship between wolves and dispersing beavers shows how wolves are intimately connected to wetland creation across the boreal ecosystem and all the ecological processes that come from wetlands.

"How large predators impact ecosystems has been a matter of interest among scientists and the public for decades," said Gable, project lead of the Voyageurs Wolf Project. "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."

Researchers found that wolves can have this impact on wetlands without necessarily changing the abundance or behavior of beavers. This newly supported link between wolf predation, dispersing beavers and wetlands may have long-lasting impacts for boreal landscapes and habitat for other species. The Voyageurs Wolf Project is investigating the long-term effects of this relationship.

"In 2015, we documented a wolf killing a dispersing beaver in a newly-created pond," said Homkes, a field biologist with the Voyageurs Wolf Project. "Within days of the wolf killing the beaver, the dam failed because there was no beaver left to maintain it. 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."

After five years of intensive fieldwork, Gable, Homkes and colleagues have estimated that wolves altered the establishment of about 88 ponds per year and the storage of over 51 million gallons of water annually in the Greater Voyageurs Ecosystem. The pond observed in 2015 still has not been colonized by another beaver, said Gable, who visited the site in mid-September 2020.

"Our work 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," said Joseph Bump, co-author and associate professor in the University's Department of Fisheries, Wildlife, and Conservation Biology.

Wolves and large predators are usually thought to have outsized ecological effects primarily by reducing the abundance of their prey or by altering the behavior of their prey through fear of predation, both of which allow predators to indirectly impact lower parts of the food chain such as vegetation, songbirds and other wildlife. Some research has even claimed wolves impact river ecosystems through trophic cascades, but this has been met with substantial skepticism and remains hotly debated among scientists.

"The fact that we have convincingly shown wolves can impact wetlands without necessarily changing the abundance or behavior of beavers is a really exciting finding," said co-author Sean Johnson-Bice, a project collaborator from the University of Manitoba.

"The Greater Voyageurs Ecosystem sits within a flat landscape that is dominated by water and trees, creating the perfect conditions that currently support some of the highest beaver densities in North America," said Voyageurs National Park wildlife researcher and co-author Steve Windels.

"Though we don't have evidence that wolves are limiting the size of the beaver population in Voyageurs, understanding the nuanced and complex ways that predators and prey affect one another and their environment is critical to fulfilling the National Park Service's mission to protect and preserve our resources for future generations."

This study identified a novel and unique way by which predators influence ecological processes, which ultimately enriches our understanding of the diverse roles predators play in ecosystems.

"There are a number of good reasons to maintain and restore healthy predator populations and this study should be helpful for understanding the full role and therefore value of predators, especially when they eat ecosystem engineers," Bump said.

What does the fox say to a puma?

VIRGINIA TECH

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IMAGE: PUMAS ARE THE TOP PREDATORS IN THE STUDY RESEARCH AREA IN THE CHILEAN ANDES. CAMERA TRAP PHOTO BY CHRISTIAN OSORIO. view more 

CREDIT: CHRISTIAN OSORIO

In the high plains of the central Chilean Andes, an ecosystem consisting of only a few animal species is providing researchers with new insights into how predators coexist in the wild.

"The puma and the culpeo fox are the only top predators on the landscape in the Chilean Andes," said Professor Marcella Kelly, of the College of Natural Resources and Environment. "And there isn't a wide range of prey species, in part because the guanacos [closely related to llamas] aren't typically found in these areas anymore due to over-hunting. With such a simplified ecosystem, we thought we could really nail down how two rival predators interact."

Kelly worked with Christian Osorio, a doctoral student in the Department of Fish and Wildlife Conservation, and researchers from the Pontifical Catholic University of Chile to chart the locations of and potential interactions between pumas and foxes in central Chile. They focused on three axes of interaction: spatial (where the animals are on the landscape), temporal (the timing of specific activities on a given landscape), and dietary (what each species is eating).

To understand the interplay between pumas and foxes, researchers deployed 50 camera stations across two sites in central Chile, one in the Rio Los Cipreses National Reserve and another on private land where cattle and horses are raised. They also collected scat samples at both locations to analyze the diets of pumas and foxes.

The team's findings, published in the journal Diversity, showed that while pumas and foxes overlapped significantly where they lived and what time they were active, there was little overlap in what they were eating, with the puma diet consisting primarily of a large hare species introduced from Europe, while the culpeo foxes favored smaller rabbits, rodents, and seeds. The two predator species can successfully share a landscape and hunt for food over the same nighttime hours because they are, in essence, ordering from different menus.

"It is likely that foxes have realized that when they try to hunt hares, they might run into trouble with pumas," Osorio explained. "If they are hunting smaller mammals, the pumas don't care, but if the foxes start targeting larger prey, the pumas will react."

How predator species interact is a crucial question for ecologists trying to understand the dynamics that inform ecosystem balances. And while the puma has been designated a species of least concern, the animal's populations are declining and continue to be monitored by conservationists.

"Least concern does not mean no concern," Osorio noted. "We have laws in Chile that protect the species, but the data we have to make a conservation designation are very scattered. As we accumulate more consistent and reliable data, the puma may be reclassified as vulnerable or even endangered."

The hares that comprise approximately 70 percent of the biomass in the puma's diet are a nonnative species, introduced to the area by European settlers. With guanacos absent from the landscape, the puma has had to adapt its diet to survive.

With some land managers and conservationists campaigning for the removal of the introduced hare species as a way to restore the area's native ecosystem, Kelly and Osorio note that it is important to understand that pumas would be significantly impacted by a reduction in their primary food source.

A further concern, which the two are currently researching, is the interplay between wildlife and humans. The national reserve increasingly sees visitors eager to witness big cats and foxes in their natural environment, while the sheep and cattle industries are increasingly using remote terrain for livestock cultivation.

"Pumas do occasionally kill livestock, which is a challenge we're looking into right now," said Kelly, an affiliate of Virginia Tech's Fralin Life Sciences Institute. "The government would like to preserve the puma, but there are competing challenges of what kind of threat they pose to livestock and what kind of threat cattle or sheep farming poses to them."

Understanding how two predatory species can come to coexist has the potential to provide conservationists and ecologists with better ideas for how humans and wild animals can share a landscape.

Controversial delisting of the US gray wolf

 

IMAGE: A GRAY WOLF; THE SPECIES WAS RECENTLY DELISTED AS RECOVERED UNDER THE ENDANGERED SPECIES ACT. view more 

CREDIT: MICHAEL LAROSA ON UNSPLASH

On 29 October 2020, the US Fish and Wildlife Service (USFWS) announced the "successful recovery" of the US gray wolf population, with US Secretary of the Interior Secretary David Bernhardt stating that the species had "exceeded all conservation goals for recovery." These claims have been rebutted by numerous experts, who argue that the delisting decision is premature. Writing in BioScience, independent ecologist Carlos Carroll and colleagues argue that the declarations of recovery should be based on a more ambitious definition of recovery than one requiring the existence of a single secure population. Instead, they propose a framework for the "conservation of adaptive potential," which builds on existing agency practice to enhance the effectiveness of the Act. The authors argue that such an approach is particularly crucial in light of climate change and other ongoing threats to species. On this episode of BioScience Talks, Dr. Carroll is joined by coauthors Adrian Treves, Bridgett vonHoldt, and Dan Rohlf to discuss the recent USFWS action as well as prospects for gray wolf conservation.