Gray wolves in Yellowstone National Park.
Gray wolves in Yellowstone National Park. Credit: Jeremy Weber

Last week, in honor of the birthday of one of the greats of conservation history, Aldo Leopold, I found myself drawn into his correspondence with Ovid Butler, editor here at American Forests (then known as the American Forestry Association) throughout much of the mid-20th century. The two wrote many letters back and forth about the needs and future of wildlife management, but one topic caught my eye. In the 40s, large predators were in decline. Sound familiar? I’d like to share two quotes I recently came across:

“The reason for over-abundance is basically the removal of native predators and the fact that game laws and guns are too crude an instrument for the control of deer without the help of native predators.”

“Large carnivores are necessary for the maintenance of biodiversity and ecosystem function. Human actions cannot fully replace the role of large carnivores.”

Awfully similar, aren’t they? Yet, the first is from a letter Leopold wrote to Butler 74 years ago. The second is from a study published just this month in Science.

We’ve made many strides over the past several decades in protecting large predators. Species like the gray wolf and the grizzly bear have made inspiring comebacks thanks largely to their protection under the Endangered Species Act in 1967 and 1975, respectively. But, the study makes clear that our work is not done. Analyzing 31 large carnivores, the researchers found that 75 percent are in decline. The reasons include habitat loss, human persecution and loss of prey.

These majestic animals have gained many an admirer for their beauty, but the reasons to protect large predatory species like wolves go far beyond their charm. When ecosystems lose their top dogs, it has cascading effects. In North America, the loss of wolves and cougars leads to increased populations of browsers like deer. Over-browsing affects all the smaller animals that depend on those plants. It can even affect the course of a stream when riparian plant life declines, leading to erosion of the stream bed.

In fact, the benefits of these large carnivores range from carbon sequestration and biodiversity to disease control and riparian restoration.

As Leopold wisely saw 74 years ago, human hunting can only go so far in mimicking the role of these predators. Our understanding of the ways these species affect their ecosystems is improving, but we still have a lot to learn. As research ecologist Rolf Peterson tells NPR, “We’re dealing with the most complicated systems in the universe, and we hardly even know what the moving parts are.”