Their findings confirm the answer to one of ecology's oldest and thorniest questions: why is the world green? It also seems to put to rest a competing theory that plants protect themselves from herbivores through physical and chemical defenses.
The researchers drew their conclusions from study of a Venezuelan valley flooded 20 years ago by a hydroelectric project.
The research, reported in the March 2006 issue of the British Ecological Society's Journal of Ecology, was supported by the National Science Foundation. The paper was co-authored by Terborgh, Kenneth Feeley and Bradley Balukjian from Harvard University, Miles Silman from Wake Forest University, and Percy Nuñez of Universidad Nacional "San Antonio de Abad" de Cusco in Peru.
Their results support the so-called "green world hypothesis," first proposed in 1960 by United States scientists Nelson Hairston, Frederick Smith and Lawrence Slobodkin. Despite being almost 50 years old, the green world hypothesis has been almost impossible to test until now.
"Since the landmark paper by Hairston et al, ecologists have been debating whether herbivores are limited by plant defenses or by predators," wrote the authors. "The matter is trivially simple in principle, but in practice the challenge of experimentally creating predator-free environments in which herbivores can increase without constraint has proven almost insurmountable."
However, the researchers realized that the hypothesis could be tested on a vast hydroelectric project.
Within Venezuela's Caroni Valley, an area of 4,300 square kilometres was flooded in 1986 to create a lake (Lago Guri) containing hundreds of island