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Species composition, coexistence and mortality factors in a carrion-exploiting community composed of necrophagous Diptera and their parasitoids (Hymenoptera)

Ulrich W.

Polish Journal of Ecology

1999

Vol. 47, no 1

49-72

In a beech forest on limestone, the community of carrion (dead Arion ater slugs) exploiting Diptera and their parasitoids (Hymenoptera) was studied. The carcass sustained 17 species of Diptera and 12 of Hymenoptera. With the exception of Kleidotoma psiloides (Eucoilidae), all of the parasitoid species bred were polyphagous and attacked all of the fly species present. The populations of the fly and wasp species were highly aggregated. The degree of aggregation depended in an inversely manner on the density. The dispersion of the parasitoids was independent from the number of hosts. Diptera, which lay their eggs in a late stage of decay, showed a negative correlation between aggregation and the weight of the slugs. There was no interspecific competition detectable between the fly species. The parasitoids did compete markedly only at high levels of parasitism. The parasitoids showed only a weak (negative) density dependent reaction to the numeber of hosts present. The degree of density dependence was more pronounced in the more infrequent species. The total parasitoid numbers increased in a linear manner with increasing host densities, and therefore the overall parasitism rate was roughly constant for different host numbers. Large predators and necrophages (Silphidae, Carabide, Arion ater) had a high impact on the mortality of the flies and wasps. in experimental boxes that allowed free access to these species, they totally prevented the development of phorid flies and their parasitoids.