Ecological Meltdown in Predator-Free Forest Fragments

• Published in: Science (American Association for the Advancement of Science) 2001-11, Vol.294 (5548), p.1923-1926
• Main Authors: Terborgh, John, Lopez, Lawrence, Nuñez, Percy, Rao, Madhu, Shahabuddin, Ghazala, Orihuela, Gabriela, Riveros, Mailen, Ascanio, Rafael, Adler, Greg H., Lambert, Thomas D., Balbas, Luis
• Format: Article
• Language: English
• Subjects: Analysis; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Ants; Ants - physiology; Anura - physiology; Araneae; Biological and medical sciences; Biotic communities; Birds - physiology; Ecological research; Ecosystem; Ecosystems; Female; Flowers & plants; Food Chain; Forests; Formicidae; Fresh Water; Fundamental and applied biological sciences. Psychology; Geography; Haplorhini - physiology; Herbivores; Holistic Approach; Iguanas; Iguanas - physiology; Insect colonies; Insect flight; Lizards - physiology; Models, Biological; Monkeys; Plants; Population Density; Power Plants; Predators; Principals; Reproduction; Rodentia - physiology; Spiders - physiology; Spiracles; Statistics; Stems; Swine - physiology; Synecology; Terrestrial ecosystems; Trees; Trees - physiology; Venezuela; World Views
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1064397

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.