Community Structure and Interaction Breadth in Beetle-Macrofungus Associations

Abstract

A major goal of ecology is to understand the factors that shape interactions among species. In this study, I explored the little-known associations between beetles and macrofungal fruiting bodies to characterize patterns of beetle-fungus association and to investigate sources of variation in the structure of these trophic interactions. First, I characterized the composition and diversity of beetle-sporocarp associations at two sites in the Appalachian Mountains and foothills, and evaluated the extent to which beetle community structure varied with fungal species, sporocarp age, and sporocarp dry mass. My results showed that beetle abundance and diversity differed among fungal species and were positively associated with sporocarp age and dry mass. I also found evidence of a nested structure in beetle-sporocarp interactions, wherein specialists on both sides of the association interact preferentially with more generalized species. Next, I performed a field study of beetle-sporocarp associations over two summers to evaluate the factors related to interaction breadth in trophic associations. I found evidence that interaction breadth varies with the palatability of the food organism (as indicated by sporocarp toughness and sporocarp age) and showed that beetle interaction breadth was negatively correlated with sporocarp persistence. I found strong intraseasonal variation in interaction breadth, but no evidence that this variation was structured by precipitation or differences in beetle community composition. In my third chapter, I conducted a field experiment to investigate (1) the importance of an individual food organism's physical properties in determining its relative importance in the beetle-sporocarp interaction network and (2) whether the structure of the beetle-sporocarp interaction network cycles predictably with the time of day. My results show that size and density of individual food organisms may be important factors in determining their relative importance in an interaction network, and offer the first evidence of diurnal cycling in the structure of interaction networks.