Metapopulation dynamics in an aphid‐parasitoid system

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Abstract
Metapopulation theory makes a number of predictions concerning the effects of dispersal on the persistence of predator‐prey or host‐parasitoid systems. While the stabilising effects of dispersal have been shown in a number of laboratory studies, evidence from field studies remains scarce due to a lack of suitable model systems. I describe a host‐parasitoid system that shows a classical metapopulation structure with frequent extinctions and colonisations consisting of the aphidiid Lysiphlebus hirticornis and the aphid Metopeurum fuscoviride. Both the parasitoid and the aphid are specialists on their respective hosts. I followed the dynamics of host and parasitoid on individually marked tansy (Tanacetum vulgare) plants, the host of M. fuscoviride. Dynamics of host and parasitoid populations were characterized by frequent extinctions and colonisations. Mean longevity of aphid colonies was only 3.1 weeks. Parasitism by L. hirticornis was a main cause of extinction for the aphid as rates of parasitism often reached 100%, in particular towards the end of the field season. Patchiness in this system occurs at two spatial scales. Aphid colonies form on single tansy ramets = shoots but movements of aphid individuals among ramets within a particular tansy genet are frequent. Because aphids can persist on a genet for a large numer of generations, it is argued that local populations form on genets rather than ramets. The number of host and parasitoid extinctions described in this study exceeds the number of extinctions usually observed in field studies of host‐parasitoid metapopulations. It is suggested that aphid‐parasitoid systems such as the one studied in this paper may be good models to test the predictions of metapopulation theory.

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