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Apex predators can help restore ecosystems, but not immediately 

The reintroduction of apex predators into ecosystems does not result in the immediate or quick restoration of those ecosystems to their original states, according to a study from Colorado State University (CSU).

The research challenges the previously held belief that the reintroduction of wolves to Yellowstone National Park fully restored the ecosystem degraded by their absence.

Absence of apex predators

The study was conducted by scientists at CSU’s Warner College of Natural Resources, focusing on the effects of three apex predators: wolves, cougars, and grizzly bears in Yellowstone. These carnivores, positioned at the top of the food chain and not preyed upon by other animals, had populations that were depleted over time. 

The return of wolves to the park in 1995 was concurrent with the natural recovery of cougar and grizzly populations. Their absence for nearly a century had significantly altered the park’s landscape and food web, transforming regions rich in willow and aspen along small streams into grasslands due to intense elk browsing. 

Alternative ecological state 

According to the researchers, the widespread changes stabilized into an alternative ecological state that resisted returning to previous conditions once the carnivores were restored.

Conducted over more than two decades, this experiment in Yellowstone is the longest of its kind. The results of the research support the theory that degradation of ecosystems may not be reversed when harmful stressors are mitigated. 

Lasting changes

“When you disturb ecosystems by changing the makeup of a food web, it can lead to lasting changes that are not quickly fixed,” said study lead author Professor Tom Hobbs. 

“We can’t rule out the possibility that the ecosystem will be restored over the next 40 years as a result of the return of apex predators. All we can be sure of is what’s observable now – the ecosystem has not responded dramatically to the restored food web.” 

Healthier ecosystems 

While it is not a quick and easy solution, said Professor Hobbs, the restoration of apex predators produces healthier ecosystems in the long run. 

“The conservation message is don’t lose them in the first place. Keep the food web intact, because there’s not a quick fix for losing top predators from ecosystems.” 

Excessive elk grazing

The researchers also explored the implications of these findings for Colorado, where Colorado Parks and Wildlife has begun reintroducing wolves following voter approval in 2020. 

Hobbs noted the differences between Colorado’s management of elk populations through hunting and Yellowstone’s policy, which led to excessive grazing and browsing by elk.

“Unlike Yellowstone, Colorado’s landscapes have not experienced widespread excessive grazing or browsing from elk,” said Hobbs. “The state has done a good job of managing elk populations using hunting.” 

Broader implications 

The researchers said there are many good reasons to restore wolves – just don’t expect them to cause immediate ecosystem improvements. 

“Our work supports the fact that wolves are important components of ecosystems,” said study co-author David Cooper, a research scientist emeritus in the Department of Forest and Rangeland Stewardship. 

“They will have some ecosystem benefits by reducing some large herbivore populations. Over the next hundred years, they’ll have a greater role in regulating some of the ecological processes that we’ve been studying.” 

Study significance 

“This research contributes greatly to our understanding of Yellowstone by teasing out the degree to which complex links in a food web affect ecosystems under native species recovery,” said Yellowstone National Park Senior Wildlife Biologist Daniel Stahler.

“Importantly, it is among few published studies to date on the Yellowstone ecosystem that highlight that not just wolves, but multiple predator species together have contributed to changes in elk abundance. This point has ramifications for how we evaluate how complex ecosystems respond to carnivore presence and absence.”

“This long-term research conducted by the CSU team also highlights the value of national parks in helping us understand ecological processes, in order to better protect ecosystems. We should not only cherish our national parks because they protect, preserve and allow people to enjoy nature, but because they provide a place where well-designed science can elevate our understanding of its complexity.” 

The study is published in the journal Ecological Monographs

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