Scientists continue to investigate the role of predatory carnivores as an indispensable element in the "green world hypothesis." The basic idea is that predators "protect" plants by controlling the population of herbivores like deer or elk, and by creating a climate of fear, which prevents these herd animals from staying in any one place too long (see "The Ecology of Fear," Currents, March/April 2006). In a recently published study supported by the National Science Foundation, researchers were afforded a rare experimental opportunity when a man-made Venezuelan reservoir created in 1986 resulted in hundreds of islands, some inhabited by predators, others predator-free.
Fourteen study sites were monitored, and nine were islands populated exclusively by herbivores. The remaining sites were on the mainland or on islands with predators. In 1997, the predator-free islands had a small sapling density 37 percent that of large land masses; by 2002, that ratio had dropped further, to 25 percent.
"The take-home message is clear: the presence of a viable carnivore guild is fundamental to maintaining biodiversity," concludes the study, which was led by Duke University environmental professor John Terborgh.