Species-environment relationships among filter-feeding caddisflies (Trichoptera: Hydropsychidae) in Rocky Mountain streams

Species-environment relationships were determined for filter-feeding macroinvertebrates from 55 Rocky Mountain stream sites to establish species distribution patterns. Species abundance and 20 environment variables were measured at each site with species-environment relationships determined using canonical correspondence analysis and stepwise multiple regression. Results suggest that the distribution of several taxa was strongly related to upstream-downstream environmental gradients. Arctopsyche grandis abundance increased with stream size (width and depth) and decreased with increasing turbulence (Reynolds number). Brachycentrus abundance also increased with stream size (depth). Hydropsyche abundance increased with increasing baseflow. Parapsyche elsis abundance demonstrated negative correlation with depth, Froude number, and conductivity. Taxa followed previously reported patterns, partitioning habitat according to stream size. Arctopsyche grandis, Brachycentrus, and Hydropsyche were found in larger (3rd- to 6th-order) streams, while Parapsyche elsis was observed in small headwater (1st- and 2nd-order) streams. Other filter-feeding taxa such as Simulium, Pisidium, and ostracods exhibited little or no apparent habitat partitioning among stream sites.