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Functional responses: a question of alternative prey and predator density
Britta Tschanz1, Louis-Felix Bersier, Sven Bacher
1Zoological Institute, Community Ecology, University of Bern, Baltzerstr. 6, CH-3012 Bern, Switzerland.
Ecology
|June 1, 2007
Summary
Alternative prey, mealworms (Tenebrio molitor), reduced predation on shield beetle larvae (Cassida rubiginosa) by decreasing the effective number of paper wasp predators. This highlights indirect ecological interactions and food web complexity.
Area of Science:
- Ecology
- Predator-Prey Dynamics
- Food Web Complexity
Background:
- Indirect species interactions significantly influence ecosystem dynamics and food web structures.
- Understanding these indirect effects is crucial for predicting ecosystem behavior.
- Previous research has highlighted the complexity introduced by indirect interactions in ecological systems.
Purpose of the Study:
- To experimentally investigate indirect interactions between two prey species sharing a common predator.
- To determine if alternative prey (mealworms) affects predation rates on a focal prey (shield beetle larvae).
- To elucidate the mechanisms through which alternative prey influences predator-prey dynamics, specifically predator interference and effective predator numbers.
Main Methods:
- A natural field experiment was conducted introducing varying densities of mealworms (Tenebrio molitor) into a paper wasp (Polistes dominulus)-shield beetle larvae (Cassida rubiginosa) system.
- The study assessed the impact of mealworms on predator interference and the effective number of predators foraging on shield beetles.
- Predation rates and prey preference were quantified to understand the functional response of paper wasps.
Main Results:
- The presence of mealworms significantly reduced the effective number of paper wasp predators.
- Predator interference among paper wasps was not significantly affected by the presence of mealworms.
- Paper wasps consistently preferred mealworms over shield beetle larvae, leading to asymmetrical indirect interactions between the prey species.
Conclusions:
- Alternative prey can indirectly influence the population dynamics of other prey species by altering predator foraging behavior.
- The study demonstrates an asymmetrical indirect interaction where increased mealworm density relaxed predation on shield beetles.
- Incorporating alternative prey dynamics is essential for accurately assessing the impact of generalist predators in ecological studies.
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