Why Toads Need Cougars

Biologists link loss of toads in national park to decline of mountain lions

• Hannah Schardt
• Feb 01, 2007

One cat can make such a difference. A new study finds that the ecosystem of a heavily touristed portion of Utah's Zion National Park has been dramatically altered by the disappearance of native cougars. William Ripple and Robert Beschta of Oregon State University found that after cougars fled the tourist influx in the 1940s, the deer population grew rapidly, destroying cottonwood seedlings and much of the other plant life in Zion Canyon. In what is known as a "trophic cascade," wildlife from butterflies to toads declined along with the cougar.

The study, published in Biological Conservation, compared the plant and animal life in the canyon with that of a neighboring area of the park, North Creek, which is not frequented by humans. "Walking into North Creek was a delight—there was such a diversity of species," Beschta says. "In Zion Canyon, you don't have that feeling at all."