Community structure and interaction breadth in beetle-macrofungus associations

Background/Question/Methods

Arthropods play important roles in the life history of many macrofungi, including ectomycorrhizal and saprotrophic species that influence plant community ecology and ecosystem function. Fungivorous insects, which feed on fungal hyphae and spores, may affect fungal fitness through spore dispersal or damage to reproductive and vegetative structures. Despite their ecological importance and capacity to serve as microcosms for understanding processes of community assembly, little is known about what shapes the composition of insect communities feeding on macrofungi. To investigate factors contributing to specialization and generalization (collectively, interaction breadth) in insect-fungal associations, we repeatedly surveyed fungal fruiting bodies (sporocarps) for adult beetles across four forest plots in two summers in the central Appalachian Mountains. Using association data from fungus-feeding beetle species, we tested the hypotheses that interaction breadth in fungivorous insects and their host fungi varies as a function of sporocarp toughness, age, and persistence, as well as over time within seasons.

Results/Conclusions

Over 68,400 adult beetles (~240 species, 28 families) were collected and identified from 1,207 beetle-hosting sporocarps (~120 species). Analyses reveal a beetle community strongly dominated by Staphylinidae, with particular abundance and diversity in the subtribe Gyrophaenina (Staphylinidae: Aleocharinae). Generalism in both beetles and fungi decreased with sporocarp toughness and increased with sporocarp age. Connectance (a measure of whole-network generalization) varied with the age structure of sporocarps in a community. Forager and host interaction breadth also varied with sporocarp persistence, and fungal interaction breadth varied strongly within seasons. This work offers new insight into the conditions shaping patterns of interaction breadth in insects and their food organisms, and represents one of the largest data sets on insect-sporocarp associations to date. We present the first investigation of interaction network structure in response to the age structure of a partner community, test novel hypotheses on the role of partner characteristics in structuring interaction breadth, and expand our understanding of within-season variation in network-wide patterns of interaction breadth.