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Updated: Jul 7, 2026
10:20
Linking Predation Risk, Herbivore Physiological Stress and Microbial Decomposition of Plant Litter
Published on: March 12, 2013
Ecological meltdown in predator-free forest fragments
1Center for Tropical Conservation, Duke University, Box 90381, Durham, NC 27708, USA. manu@duke.edu
Science (New York, N.Y.)
|December 1, 2001
Summary
Predators control herbivore populations, preventing overgrazing. On predator-free islands, increased herbivore densities led to reduced tree seedling survival, demonstrating top-down ecosystem regulation.
Area of Science:
- Ecology
- Ecosystem Regulation
- Trophic Cascades
Background:
- Controversy exists regarding terrestrial ecosystem regulation: top-down (predator control) vs. bottom-up (plant defenses).
- Predator-free islands created by hydroelectric impoundment in Venezuela offer a unique natural experiment.
Purpose of the Study:
- To test competing theories of ecosystem regulation (top-down vs. bottom-up).
- To investigate the impact of predator absence on herbivore populations and vegetation.
Main Methods:
- Studied small islands (0.25-0.9 hectare) with limited fauna, lacking vertebrate predators.
- Compared densities of rodents, howler monkeys, iguanas, and leaf-cutter ants on islands versus the mainland.
- Assessed densities of canopy tree seedlings and saplings on herbivore-affected islands.
Main Results:
- Herbivore densities (rodents, monkeys, iguanas, ants) were 10-100 times higher on islands than the mainland.
- Seedling and sapling densities of canopy trees were significantly reduced on islands.
- Absence of vertebrate predators led to increased herbivore populations and subsequent vegetation reduction.
Conclusions:
- Findings support the top-down regulation theory in terrestrial ecosystems.
- Predator absence can unleash trophic cascades, severely impacting plant communities.
- Ecosystem structure is significantly influenced by the presence and activity of predators.
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