Filters and templates: stonefly (Plecoptera) richness in Ouachita Mountains streams, U.S.A

1. We collected adult stoneflies periodically over a 1-year period at 38 sites in two headwater catchments in the Ouachita Mountains, Arkansas, U.S.A. The 43 species collected were a subset of the Ozark-Ouachita fauna and the much larger fauna of the eastern U.S.A. We estimated 78–91% species coverage in the two catchments using jackknife extrapolation of species richness from our survey. 2. Many streams, especially small ones, lacked surface water for months, but others, both small and large, flowed permanently. 3. Using published regional presence–absence and coarse ecological data in a discriminant function analysis (DFA), we identified stream size (negative) and regional frequency of occurrence (positive) as predictors of presence in these headwater catchments. For the combined catchments, the extrapolated richness (51 spp.) was similar to an estimate (48 spp.) based on predicted absences from DFA and the Ouachita provincial total of known stonefly species (57 spp.). 4. Local species richness (1–27 spp. per site) was correlated strongly with stream size (catchment area) but was independent of stream drying. Generic richness was correlated negatively with stream drying and positively, but less strongly, with stream size. 5. Regionally endemic stoneflies dominated in drying streams, and widely distributed species dominated in more permanent streams. The composition of stonefly assemblages was associated with regional factors (species pools, regional abundance, evolution of tolerant endemic species, regional climate) and local factors (drying, stream size).