Microhabitat associations of three species of Dryopoidea (Coleoptera) in an Ozark stream: a comparison of substrate, and simple and complex hydraulic characters

Microhabitat associations of adults and larvae of Stenelmis lateralis Sanderson, Optioservus sandersoni Collier (Coleoptera: Elmidae) and larvae of Psephenus herricki (DeKay) (Coleoptera: Psephenidae) were examined within riffles of an Ozark stream in Missouri. The invertebrate fauna was sampled from 150 quadrats, and each quadrat was characterized by a suite of substrate, simple hydraulic, and complex hydraulic variables. Larvae were assigned to size classes for analyses. MANOVAs were performed to determine if differences existed between sites of presence and absence for each of the three species separately. Subsequently, ANOVAs and Bonferroni sequential adjustments were performed to determine differences in each habitat variable that are related to presence or absence of each group. Multiple regression was performed to determine which habitat variables were important determinants of density for each taxon. Finally, discriminant function analyses were performed to determine the degree of overlap in microhabitat associations of each group. A clear distinction was seen between sites of occurrence and absence for P. herricki, and for larvae of each elmid species (MANOVAs). For P. herricki, current velocity and the complex hydraulic characteristics of Reynolds number and boundary Reynolds number were important in determining beetle presence. In contrast, substrate characteristics were major determinants of presence for larvae of O. sandersoni and S. lateralis. In general, the density of each of the three species was related to a different subset of abiotic variables. For each species, the most definitive microhabitat associations were seen in the early instars. Microhabitat associations for larvae of each elmid species were size class-specific. Inclusion of complex hydraulic characteristics along with substrate and simple hydraulic characteristics provided greater resolution of microhabitat associations.