Gray Wolves in Yellowstone National Park

Historically, the habitat of gray wolves (Canus lupus) in the US ranged across the entirety of the northern US, stretching down through the Southwest to Texas

Historical Range

William J. Ripple, Robert L. Beschta, 

Trophic cascades in Yellowstone: The first 15 years after wolf reintroduction

As of 2009, there are three well-studied populations of grey wolf:  Norther Rocky Mountain population, Western Great Lakes population, and Mexican population.

Current Range
William J. Ripple, Robert L. Beschta

What caused such a drastic reduction in the range of the gray wolf?
Since colonists first came to North America, gray wolves have been viewed as threats to livestock and, at times, to humans.  In the late 1800s to the early 1900s, bounties were placed on gray wolves, particularly in the Western United States (Boyd, 2006).  By the early 1900s, much of the range of the gray wolf had been drastically reduced.  Popular feelings and beliefs about wolves, and the roles they play in the environment, began to change mid-century.  In 1973, the U.S. government passed the Endangered Species Act.  The gray wolf was on the list.

Starting in 1995, the gray wolf was reintroduced to Yellowstone National Park, from populations in Canada, after having been absent from the area for approximately 70 years.  This introduction provided scientists with an opportunity to study trophic cascades and their impacts on the environment.

Gray wolves have now been present in the Yellowstone National Park for the past 15 years.  In a study done by Ripple et al, increasing wolf populations in the park have led to a significant decrease in the number of elk.  This change is healthy.  It has allowed for an increase in both bison and beaver populations, species whose dwindling numbers indicated a possible addition to the ever increasing at risk list.  Because of the decrease in the elk population, browsal percentage dropped.  Aspen, Cottonwood, and Willow tree stands saw a significant increase in rate of regeneration.


Since the reintroduction of the gray wolf into Yellowstone National Park in the 1970's, the wolf - elk - plant community cascade is in the process of being restored.  Results are not immediate and progress is slow, but hopeful.