"This is a terrific contribution to a growing body of evidence that [cascades] occur in major terrestrial systems," says Paine, who coined the term "trophic cascade" in 1980. Recent studies of shrinking numbers of wolves in Yellowstone National Park have shown similar effects on plant-life.
Restoring at least part of the cougar population could, over time, rebalance Zion's ecosystem. One way to boost the number of predators might be to limit vehicle access to the park, speculates Ripple. When the park implemented a bus system that reduced car traffic in 2000, he says, cougar sightings increased.