NESTED SUBSET STRUCTURE OF LARVAL MYCOPHAGOUS FLY ASSEMBLAGES - NESTEDNESS IN A NON-ISLAND SYSTEM

Nested subset structure has been studied in archipelagoes and fragment ed habitats, and has been attributed to differential colonization and extinction rates among species and nested environmental tolerances. In this experiment, we tested for nestedness in assemblages of mycophago us fly larvae. Twenty mushrooms in each of three size classes (4.8-6.0 g, 10-15 g, 21-32 g) were placed on moist potting soil in experimenta l cups. The cups were placed in oak and pine forests in Greenville, S. C., USA for 5 days, where they were available to ovipositing flies. Up on collection, the mushrooms were incubated in the laboratory for 3 we eks and all emerging flies were sorted by species, counted, and weighe d. A random placement analysis was conducted to determine whether the species richness pattern was a sampling artifact of the species abunda nce distributions. The actual species richness pattern did not conform to the random placement model; most mushrooms contained significantly fewer species than predicted by random sampling. The communities were strongly nested as measured by two different indices, and the nestedn ess pattern was related to mushroom size. Small mushrooms usually prod uced no flies or a single species, Dohrniphora sp. (Phoridae). Medium and large mushrooms typically produced more species-rich communities t hat usually contained the phorid and Drosophila putrida, D. tripunctat a, and Leucophenga varia. This core guild was nested within a more div erse assemblage that included D. falleni, Mycodrosophila dimidiata, a muscid, and two Leptocera sp. (Sphaeroceridae). These patterns are ten tatively explained in the context of nested desiccation tolerances, me diated by differences in mushroom size.