7 Keystone Species — and Why they Matter for Our Planet

Wolves have long played a dual role in the human imagination ­— untamable wild spirits on the one hand and dangerous, shape-shifting predators on the other. We hunted wolves to the point of extinction to save our livestock and protect ourselves. Or so we believed.

Our efforts to control them brought repercussions. The loss of wolves in the natural order affected other species, as well as the environment, in ways we could never have imagined.

We soon discovered that wolves are a keystone species — animals or plants that are essential to the optimal function or structure of their ecosystem. Their impact is felt from the top down or the bottom up.

“Keystone species have low functional redundancy,” explains biologist Raquel Filgueiras of the conservancy group Rewilding Europe. “This means that when populations of these species decline or disappear, there are very few or no other species that can fulfill their role. Ecosystems then degrade, and sometimes completely collapse.”

Wolves are one of many keystone species that humans have viewed as pests or, even worse, enemies to control or remove.

Running Without the Wolves

When Yellowstone National Park was established in 1872, wolves were already in decline nationwide as a result of ­human westward expansion. The legislation that created the park provided no protection for wolves or other large predators. By 1926, government control programs sealed the fate of gray wolves in the park’s ecosystem, and by the early 1970s, wolves had been nearly eliminated from the lower 48 states.

In Yellowstone, the absence of wolves set off a cascade of events. Elk populations expanded, and because they didn’t have to constantly be on the move to avoid wolf packs, their grazing habits changed. Settling in one place for a longer time, the elk foraged on cottonwood, aspen, and willow trees, devastating these forests.

This in turn degraded valleys and meadows, which became dry and bare, decimating the birds, insects, and mammals, such as beavers, that relied on them.

After Congress passed the Endangered Species Act of 1973, wolf populations made a comeback. They were reintroduced to Yellowstone in 1995.

The wolf packs have since kept the elk circulating through the landscape. “Elk have proven to be pretty adaptable. When wolves are around, they’re more vigilant and do less foraging,” explains Montana State University ecology professor Scott Creel, PhD.

The change in elk behavior allowed meadows, valleys, and forests to regenerate. And small mammals could find food and shelter again, which attracted raptors back to the area.

Building Beavers

The wolves’ return also aided beavers. North America’s largest rodents are essential ecosystem engineers, and they now had a plentiful supply of leaves, roots, and bark to eat, and wood for building dams.

Beaver dams can be a nuisance for humans: They may divert waterways where we don’t want them and cause flooding; the trees beavers cut down can destroy our sense of the picturesque.

But beaver dams play a grander role in the ecosystem that we may not comprehend. They slow water flow in streams, which can help reduce erosion and provide water during drought. The flowage behind these dams creates wetlands, which can absorb seasonal flooding. And the wetlands filter water, replenishing aquifers and producing cleaner water for all.

Other mammals, fish, amphibians, insects, and birds depend on the beaver’s dam-building. Some 85 percent of North American wild-animal species rely on wetlands — including many threatened and endangered species.

The beavers’ work is also becoming recognized as key to fighting wildfires. Not only do their dams retain water in the land-scape, but channels dug by beavers -appear to act like irrigation canals, keeping vegetation too wet to burn even during droughts. These wetlands become a beaver-generated safe space for frogs, salamanders, birds, and other animals to wait out a fire.

Since colonial times, however, we humans have drained vast swaths of wetlands for our own uses. Beavers are industriously working to right this wrong — when we let them.