Effects of Resource Density on Mycophagous Fly Dispersal and Community Structure

Abstract

I censused adult flies visiting 1-m2 plots containing high or low densities of a natural host-mushroom analog (Agaricus bisporus). I also conducted a mark-recapture experiment with visiting drosophilids. More individuals and species were captured in high density plots than low density plots, and species used high density plots more frequently. Also, mycophagous drosophilids localized activity in rich resource areas and dispersed more readily from poor resource areas. These patterns are consistent with the 'trapping effect' predicted for dense resource patches in the resource concentration hypothesis. I also collected mushrooms from plots and censused flies that emerged. In contrast to the resource concentration hypothesis, there was no evidence of the establishment of a dominance hierarchy in response to increased resource density. Single mushrooms in the high density plots produced more diverse, species-rich communities, with less dominance and greater resource overlap, than single mushrooms in low density plots. Persistent patches of mushrooms may accumulate species, but the ephemerality of individual resource units may preclude the establishment of large populations and maintain communities in a high diversity state.