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  • Writer's pictureNotes From The Frontier

Yellowstone's Keystone Wolves

Updated: Feb 20, 2020

A century ago, gray wolves were completely exterminated from Yellowstone National Park. (In fact, the wolf had been exterminated from nearly all of the mainland United States.) With the loss of the apex predator in Yellowstone, an ecosystem collapse was triggered. Biologists call this a “trophic cascade.” That cascade affected species of animals and plants from the largest to the smallest not only in Yellowstone, but the rest of the continent.

At the time, the world did not understand the natural symbiosis and complex hierarchy Nature had devised over millions of years. Human beings primal fear of apex predators reigned and there was a concerted effort to clear the land of all large and dangerous predators—especially wolves, bears, and cougars—for human settlement of the land. Little was understood or considered about the crucial role these predators played in the ecosystem. 

This year marks the 50th anniversary when the first scientist identified the concept of “keystone species.” Zoologist Robert Paine discovered in 1969 that certain species are especially crucial to the stability of the environment. In the beginning, scientists believed that keystone species were only apex predators. Since then the concept has been greatly expanded. But the basic concept has remained a core principle of environmental science. In a nutshell, when keystone species disappear, lower species take over the environment.

Paine first discovered this concept by researching starfish in tidal pools off the coast of Washington. When he removed the starfish, their prey decimated the ecosystem, stripping it of all vegetation and other life. Likewise, when wolves were gone from Yellowstone and other areas, elk and deer became vastly overpopulated. When sea otters were hunted to near extinction for their fur, sea urchins destroyed the underwater kelp forests and many other species. Hunting and habitat loss have driven the jaguar to near extinction in North, South and Central America, which has caused their herbivorous prey—deer, tapirs, and capybaras—as well as monkeys, to nearly decimate forest foliage. In much of mainland United States the loss of apex predators had caused out-of-control deer and coyote populations. 

The relationship that wolves have to the environment is far more complex than simply hunting and eating elk and deer. In 1995, the Endangered Species Act was enacted and the DNR and conservationists reintroduced the wolf to Yellowstone.

The impact was dramatic far beyond the obvious. Elk populations had exploded with the loss of their primary predator. That resulted in severe and concentrated overgrazing, especially of willows and aspen that beavers relied on for food, dam building and habitat. Beaver dams had created marshy ecosystems for aspen and willow and many other plant and animal species. When the beaver disappeared, many other species were decimated as well, especially cutthroat trout and other fish, amphibians, such as salamanders and frogs, reptiles such as turtles and snakes, songbirds, small mammals, and insects. Marshes turned into streams, which eroded the land. And concentrated grazing and watering of elk herds and deer further degraded the stream banks. With the loss of the wolf, coyotes also became the apex predator and over-populated, thereby diminishing the pronghorn antelope, red fox and other smaller mammals. With the reintroduction of the wolf, those species returned. Wolf kills also provided food for many other apex predators, such as grizzlies, cougars, and eagles.

One of the governing concepts of keystone species is what ecologists call “the landscape of fear.” Predators, understandably, instill fear in prey. This fear dictates how prey behave. Wide open areas with long lines of sight give prey a head start in fleeing attacking predators. So grazing animals tend to graze in these broad, open areas and also disseminate their nutrient-rich manure across these large areas. They avoid thick foliage and marshy areas where predators may lurk. But with those predators gone, all vegetation is “open season” and habitats that normally existed with large predators disappear. This pattern has been observed across the globe by scientists. 

When Yellowstone was declared the nation’s first national park in 1872, there were no protections for wolves at the time and it was an era of mass killing to near extinction of many apex species. By 1926, as a result of mass hunting, as well as state and federal predator control efforts, wolves were extirpated (locally extinct) in Yellowstone. In 1973, the federal Endangered Species Act began protecting wolves. In 1995, and 1996, 31 wolves were introduced back into Yellowstone Park.

The park introduction was part of a larger effort to bring back wolves in the Northern Rocky Mountain region. Under federal protection and with an over-abundance of elk, wolves thrived in the park. By 2002, the U.S. Fish and Wildlife Service met the prescribed goal of establishing 30 breeding pairs of wolves in Yellowstone. 

According to the Yellowstone Park website, this year there were about 60 wolves in Yellowstone park (as of Sept. 19, 2019) distributed in about eight different packs. The population fluctuates from year to year. In 2018, there were about 80 wolves in nine packs, and in 2017, 97 wolves in 11 packs. Although wolves are protected within the boundaries of Yellowstone, six were illegally killed by humans in 2018. Others were killed by litter loss (the pups starve if the parent/s are killed), some were killed by a virus or parvo, some were driven out by competing packs. And others are legally killed by hunters when they range outside the boundaries of Yellowstone, where controlled hunts are legal in Montana, Idaho, and Wyoming, adjacent to National Park land.

The reintroduction of wolves as an apex predator and keystone species has brought dramatic benefits to the national park ecosystem. According to the Yellowstone Park website, only ONE beaver colony was in the park when wolves were introduced in 1995. Now there are nine colonies.


“The reintroduction of wolves continues to astonish biologists with a ripple of direct and indirect consequences throughout the ecosystem,” according to Yellowstone’s site. “Ecosystems are incredibly complex. In Yellowstone, biologists have the rare, almost unique, opportunity to document what happens when an ecosystem becomes whole again, what happens when a key species is added back into the ecosystem equation. Wolves triggered a still-unfolding cascade effect among animals and plants – one that will take decades of research to understand.”

Ed Bangs, the wolf recovery coordinator for the U.S. Fish and Wildlife Service in Yellowstone, said he was genuinely surprised by the extensive web of life that is linked to wolves. "Beetles, wolverine, lynx and more," he said. "It turns out that the Indian legends of ravens following wolves are true. Wolves mean food.” 

Two excellent documentaries about Yellowstone’s wolves and other keystone species are:

• The 2019 film, “The Serengeti Rules,” Episode 38 of the PBS’s NATURE series. The award-winning documentary can be viewed on YouTube at: | #NaturePBS OR ,

your local PBS (Public Broadcasting Service), on Amazon Prime or go to: .

• The award-winning 2007 film, “In the Valley of Wolves,” PBS NATURE series, , chronicles the struggles of the Druid wolf pack in Yellowstone National Park. 

PHOTOS: (1) The gray wolf is an apex predator in Yellowstone National Park, as well as a “keystone species,” crucial to maintaining the entire ecosystem of the park. In recent decades, scientists have discovered that “keystone species” are lynchpins in the complex biological relationships in various ecosystems all over the globe. (2) Wolves were re-introduced to Yellowstone in 1995. In the last 25 years, they have thrived and helped Yellowstone’s ecosystems rebound, reducing elk herds, enabling willow and aspen groves to return, and reintroduced beaver, songbird and other species populations. (3) According the Yellowstone Park website, there are about 60 wolves in Yellowstone park (as of Sept. 19, 2019) distributed in about eight different packs. The population fluctuates. In 2018, there were about 80 wolves in nine packs, and in 2017, 97 wolves in 11 packs. Wolves are protected in Yellowstone but six were illegally killed by humans in 2018. Others were killed by litter loss (the pups starve if the parent/s are killed), some were killed by a virus or parvo. Some were driven out by competing packs. (4) A bull Elk in a stand-off with a pack of wolves. Some elk can fight off wolves. Wolves usually scope out the weakest in the herd. (5) Elk are often caught in rivers when they try to escape pursuing wolves. (6, 7 & 8 ) The return of wolves as a “keystone species” at Yellowstone has had dramatic effects on Yellowstone’s ecosystems and beaver, cutthroat trout, eagles and many other species have returned to the park, primarily because wolves have reduced overpopulation of elk herds that decimated the land.


Posted October 12, 2019

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Deborah Hufford

Author, Notes from the Frontier

Deborah Hufford is an award-winning author and magazine editor with a passion for history. Her popular blog with 100,000+ readers has led to an upcoming novel! Growing up as an Iowa farmgirl, rodeo queen and voracious reader, her love of land, lore and literature fired her writing muse. With a Bachelor's in English and Master's in Journalism from the University of Iowa, she taught students of Iowa's Writer's Workshop, then at Northwestern University, Marquette and Mount Mary. Her extensive publishing career began at Better Homes & Gardens, includes credits in New York Times Magazine, New York Times, Connoisseur, many other titles, and serving as publisher of The Writer's Handbook


Deeply devoted to social justice, especially for veterans, women, and Native Americans, she has served on boards and donated her fundraising skills to Chief Joseph Foundation, Missing & Murdered Indigenous Women (MMIW), Homeless Veterans Initiative, Humane Society, and other nonprofits.  


Deborah's soon-to-be released historical novel, BLOOD TO RUBIES weaves indigenous and pioneer history, strong women and clashing worlds into a sweeping saga praised by NYT bestselling authors as "crushing," "rhapsodic," "gritty," and "sensuous." Purchase BLOOD TO RUBIES online beginning June 9. Connect with Deborah on, Facebook, and Instagram.

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