SPECIES-ENVIRONMENT RELATIONSHIPS AMONG FILTER-FEEDING CADDISFLIES (TRICHOPTERA, HYDROPSYCHIDAE) IN ROCKY-MOUNTAIN STREAMS

Species-environment relationships were determined for filter-feeding m acroinvertebrates from 55 Rocky Mountain stream sites to establish spe cies distribution patterns. Species abundance and 20 environmental var iables were measured at each site with species-environment relationshi ps determined using canonical correspondence analysis and stepwise mul tiple regression. Results suggest that the distribution of several tax a was strongly related to upstream-downstream environmental gradients. Arctopsyche grandis abundance increased with stream size (width and d epth) and decreased with increasing turbulence (Reynolds number). Brac hycentrus abundance also increased with stream size (depth). Hydropsyc he abundance increased with increasing baseflow. Parapsyche elsis abun dance demonstrated negative correlation with depth, Froude number, and conductivity. Taxa followed previously reported patterns, partitionin g habitat according to stream size. Arctopsyche grandis, Brachycentrus , and Hydropsyche were found in larger (3rd- to Gth-order) streams, wh ile Parapsyche elsis was observed in small headwater (1st- and 2nd-ord er) streams. Other filter-feeding taxa such as Simulium, Pisidium, and ostracods exhibited little or no apparent habitat partitioning among stream sites.