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Invading parasitoids suffer no Allee effect: a manipulative field experiment
Xavier Fauvergue1, Jean-Claude Malausa, Ludovic Giuge
1Institut National de la Recherche Agronomique (INRA), 400 Route des Chappes, 06903 Sophia Antipolis Cedex, France. xavier.fauvergue@sophia.inra.fr
Ecology
|October 9, 2007
Summary
Biological invasions can fail due to the Allee effect, where small populations struggle to establish. This study on parasitoid wasps found no Allee effect, suggesting their traits may prevent invasion failure.
Area of Science:
- Ecology
- Invasion Biology
- Population Dynamics
Background:
- The Allee effect, a decline in population growth at low densities, is a frequent explanation for the failure of biological invasions.
- Biological control introductions offer a unique experimental system to test for Allee effects due to manipulable initial population sizes.
Purpose of the Study:
- To experimentally test for the occurrence of Allee effects in a parasitoid wasp introduced for biological control.
- To investigate the impact of initial population size on the establishment and population dynamics of the invasive parasitoid.
Main Methods:
- Manipulated the initial population size of 45 parasitoid wasp populations.
- Monitored parasitoid and host population dynamics over three years.
- Assessed establishment probability, net reproductive rate, sex ratio, and host population depression.
Main Results:
- Establishment probability after three years was independent of initial population size.
- Net reproductive rate was highest at low parasitoid density and high host density.
- Low parasitoid densities did not impede mate-finding, and host population depression was not dependent on introduced parasitoid numbers.
Conclusions:
- The study found no evidence of Allee effects in the introduced parasitoid wasp.
- Negative density dependence was observed, with higher reproductive rates at lower densities.
- Behavioral and life-history traits of parasitoids may confer resistance to Allee effects, aiding biological control success.
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