Terborgh and his team monitored the vegetation at 14 sites of differing size. Nine of the sites were on predator-free islands, while the others were on the mainland or on islands with a complete or nearly complete suite of predators.
They found that, by 1997, small sapling densities on small islands were only 37 percent of those of large land masses and by 2002 this had fallen to just 25 percent. Most of the vertebrates present in regional dry forest ecosystem had disappeared from small islands, including fruit eaters and predators of vertebrates, leaving a hyperabundance of generalist herbivores such as iguanas, howler monkeys and leaf-cutter ants.
"Mere numbers do not do justice to the bizarre condition of herbivore-impacted islets," the authors wrote. "The understory is almost free of foliage, so that a person standing in the interior sees light streaming in from the edge around the entire perimeter. There is almost no leaf litter, and the ground is bright red from the subsoil brought to the surface by leaf-cutter ants.
"Dead twigs, branches and vine stems from canopy dieback litter the ground, and in places lie in heaps. But in striking contrast with this scenario of destruction, the medium islands presented a relatively normal appearance."
Besides proving that the green world hypothesis is correct, Terborgh's team's results have important implications for the debate raging in many countries over reintroduction of top predators such as wolves. "The take-home message is clear: the presence of a viable carnivore guild is fundamental to maintaining biodiversity," the authors wrote.
Information collected for the Journal of Ecology report is a five-year update of results published by Terborgh and 10 other scientists in the Nov. 30, 2001, issue of the journal Science.
"The Science article reported on the first plant census we did, involving 15,000 plants,