Habitat configuration affects spatial pattern of β diversity of insect communities breeding in oyster mushrooms

Theory predicts that spatial structure can mediate interactions that affect species diversity in a patchy environment. A rarely considered effect of spatial structure on biodiversity is the interplay of spatial habitat arrangement with species interactions at multiple spatial scales. We investigated how spatial habitat arrangement and predation mediate the assembly of the larval communities of fungivorous insects breeding in the oyster mushroom, Pleurotus ostreatus (Jacq. ex Fr.) P.Kumm in a North American woodland. In a two-way factorial design, we varied the spatial arrangement of mushroom clumps ('clustered', 'patchy', and 'uniform'; 3 levels) crossed with predator exclusion (access allowed or not; 2 levels) to study their joint effects on patterns of alpha, beta and gamma diversity of the fungivorous insect communities. Partitioning diversity into these three components suggested that neither spatial nor predation treatments significantly affected alpha, beta and gamma diversity. We found that an intermediate inter-clump distance (i.e., the 'patchy' treatment) increased spatial autocorrelation in insect community composition within experimental blocks, particularly in the mushrooms to which predators had access. The spatial structuring in b diversity indicates that the arrangement of mushroom clumps can structure beta diversity of fungivorous larval communities through direct effects on the species themselves (e.g., increased aggregation and habitat choice of ovipositing females of fungivorous insects), as well as effects mediated through the presence and behavior of predators (e.g., spatially structured selective foraging by predators acting as a filter on which species were in the clumps). The naturally patchy nature of mushroom fruiting may transform the spatial pattern of beta diversity by altering the behavior of ovipositing females, or by weakening the negative effect of larval competition.