Gray wolves were reintroduced into Yellowstone National Park in 1995, resulting in a trophic cascade through the entire ecosystem. After the wolves were driven extinct in the region nearly 100 years ago, scientists began to fully understand their role in the food web as a keystone species.
TRANSCRIPT: In 1995, something really exciting happened in the nation’s first national park, Yellowstone. 41 wild wolves are reintroduced here by scientists. After 100 years of being hunted, wolves could once again call this place home.
The wolves thrived, but something else very surprising happened. Their return had a spectacular effect on the landscape, an effect that spread wider than anyone thought possible. So how did this all happen?
In the past, wolves were seen as a risk to people and livestock, and they were exterminated from the Yellowstone area in the 1920s. The elk’s main predator was gone, and their population more than doubled. Elk are both grazers and browsers, so they eat grass, shrubs, and trees. They overgraze the entire park, upsetting the natural balance of the ecosystem.
Mammals like mice and rabbits could not use the plants to hide from predators, and their populations fell dramatically. Grizzly bears suffered as the elk munch away their berry supply, which they badly need to build up fat before hibernating. Pollinators like bees and hummingbirds had fewer flowers to feed on, songbirds less trees to nest in.
Perhaps the elk’s most devastating impact was how they affected the park’s riverbanks. When the wolf was around, elk were vulnerable when they moved down towards rivers to drink. They would never spend too long by the water, where they could be ambushed. But with the apex predators gone, they gorged themselves faster than the shrubs could grow and gathered in great herds on the lush river banks. The massive elk’s hooves eroded the riverbanks, so the rivers and streams clouded with soil.
The fish inherited murky homes, and without trees and clean water, beavers couldn’t build their dams to live in. Without the protection of the dams, fish, amphibians and otters suffered even more, and all because of the missing wolf.
Now, with as many as 100 gray wolves in Yellowstone National Park, their reintroduction is having an effect that even surprised scientists. Wolves have contributed to bringing elk numbers down from 17,000 in 1995 to just 4,000 today. Since only the healthiest of elk survived, the population is much more robust.
All of these elk kills mean more carcasses for scavengers like coyotes, eagles, and ravens. Grizzly bear numbers have increased, too. The grizzlies benefit from the wolves’ elk kills, and less elk also means more berries, and just the elk’s fear of wolves gives the riverbank trees, like aspen and willow, a chance to regenerate. They can grow to five times their original size in just six years.
The songbirds are returning, too, and the bigger trees along the rivers means greater root structures, which means stronger riverbanks and less erosion. Clean water and big trees, beaver paradise. The return of the beaver dams creates new habitats for fish, amphibians, reptiles, and even otters.
This shows just some of the trickle-down effects of the wolves’ reintroduction, known to scientists as a trophic cascade. The trophic cascade doesn’t stop there, though. The wolves are even helping us. In 2005, over 100,000 visitors went to Yellowstone National Park just to see the wolves, pumping $30 million into the local economy, money for jobs and livelihoods.
Factor in that wolves contribute to the health and diversity of all Yellowstone’s wildlife, and its impact is staggering. The wolf’s benefits also cascade down to the 106,000 residents of Billings, Montana. Their drinking water, Yellowstone River, is now cleaner. Who would’ve thought that just bringing back some wolves could produce such far-reaching benefits for nature and for people? From the tips of taller trees down to its cleaner rivers, these wild wolves have rebalanced and restored our nation’s very first national park.
Wow, just wow.
