You may have heard that one thing in an ecosystem can affect every other thing in that ecosystem. In Yellowstone we are watching the ripple effect caused by the return of the gray wolf. Wolves were exterminated by the 1930s and absent from the park for decades until reintroduced in 1995.

Now that wolves are back, researchers are discovering how they affect other species in the park. Though the coyote population increased during the wolves’ absence, wolves are now reducing the number of coyotes in areas of the park where they compete for prey. Pronghorns could benefit since coyotes prey heavily on pronghorn fawns. Fewer coyotes could lead to an increase in fox because those two animals compete for smaller prey species like rodents.  

Since elk are the most common prey of wolves in Yellowstone, their numbers are coming down from an all-time high reached while wolves were gone. Because wolves kill the weakest animals, they make elk herds healthier by removing the old, young and infirm. Elk may change their movements, distribution, and foraging behavior now that wolves are back.

Changes in elk browsing patterns could lead to increased growth in aspen and willow communities, which could affect other animals and birds like the yellow warbler and willow flycatcher. There is already an increase in beaver colonies in the Northern Range of the park where the wolf population density is highest.

When wolves kill prey to eat, many scavengers take part in the feast. Grizzly bears, coyotes, ravens, magpies, eagles and numerous insects all eat from wolf-killed carcasses. Grizzly bears repeatedly steal carcasses from some wolf packs in the park. With bears getting food from wolves, will they have more cubs or shorten their hibernation? Will they find less winter-killed carcasses to eat when they emerge from their winter dens since wolves have already taken the weakest prey animals over the winter?  Will bears learn to follow wolf packs and let wolves do the hunting for them?

The effect wolves have on so many plants and animals is teaching us more about them and their role in the complex web of this ecosystem. There’s still much to learn. Though wolves are only one piece to the vibrant puzzle that is Yellowstone, it’s exciting to witness the comeback of a threatened species as wolves reclaim their place here.

Video © 2008 Yellowstone Park Foundation