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Science 30 November 2001:
Vol. 294. no. 5548, pp. 1923 - 1926
DOI: 10.1126/science.1064397
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Reports

Ecological Meltdown in Predator-Free Forest Fragments

John Terborgh,1* Lawrence Lopez,2 Percy Nuñez,3 Madhu Rao,45 Ghazala Shahabuddin,6 Gabriela Orihuela,7 Mailen Riveros,8 Rafael Ascanio,9 Greg H. Adler,11 Thomas D. Lambert,10 Luis Balbas12

The manner in which terrestrial ecosystems are regulated is controversial. The "top-down" school holds that predators limit herbivores and thereby prevent them from overexploiting vegetation. "Bottom-up" proponents stress the role of plant chemical defenses in limiting plant depredation by herbivores. A set of predator-free islands created by a hydroelectric impoundment in Venezuela allows a test of these competing world views. Limited area restricts the fauna of small (0.25 to 0.9 hectare) islands to predators of invertebrates (birds, lizards, anurans, and spiders), seed predators (rodents), and herbivores (howler monkeys, iguanas, and leaf-cutter ants). Predators of vertebrates are absent, and densities of rodents, howler monkeys, iguanas, and leaf-cutter ants are 10 to 100 times greater than on the nearby mainland, suggesting that predators normally limit their populations. The densities of seedlings and saplings of canopy trees are severely reduced on herbivore-affected islands, providing evidence of a trophic cascade unleashed in the absence of top-down regulation.

1 Center for Tropical Conservation, Duke University, Box 90381, Durham, NC 27708, USA.
2 Department of Biological Sciences, Florida International University, Miami, FL 33199, USA.
3 Herbario Vargas, Universidad Nacional "San Antonio de Abad" de Cusco, Cusco, Peru.
4 Wildlife Conservation Society, 2300 South Boulevard, Bronx, New York, NY 10464, USA.
5 Conservation Biology Group, Department of Zoology, Downing Street, Cambridge University, Cambridge CB2 3EJ, UK.
6 Chintan Environmental Research and Action Group, 238 Siddhartha Enclave, New Delhi 110014, India.
7 Universidad Ricardo Palma, Facultad de Ciencias Biológicas, Jose Gonzales 684, Lima 18, Peru.
8 Fundación Museo de Ciencias/Centro Adolfo Ernst, Apartado Postal 5883, Caracas 1010, Venezuela.
9 Universidad Complutense de Madrid, Departamento de Ecología, Facultad de Ciencias Biológicas, Ciudad Universitaria, 28040 Madrid, Spain.
10 Faculty of Forestry, University of Toronto, Ontario M5S 3B2, Canada.
11 Department of Biology and Microbiology, University of Wisconsin Oshkosh, 800 Algoma Boulevard, Oshkosh, WI 54901-8640, USA.
12 EDELCA, Apartado 28, Puerto Ordaz, Estado Bolívar, Venezuela.
*   To whom correspondence should be addressed: E-mail: manu{at}duke.edu

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