Scales of macroinvertebrate distribution in relation to the hierarchical organization of river systems

The multiscale distribution of macroinvertebrate assemblages may correspond to the hierarchical arrangement of river systems because geomorphological processes manifest characteristic environmental conditions at different scales. Macroinvertebrates were sampled according to a nested hierarchical design incorporating 4 geomorphologically derived scales: catchment, zone, reach, and riffle. Analysis of Similarity, mean similarity dendrograms, and nested analysis of variance were used to determine the scale(s) at which macroinvertebrate assemblages differed. Macroinvertebrate assemblages were similar among riffles within a reach, but were dissimilar at the zone and catchment scales. There also was a regional-scale pattern of macroinvertebrate distribution that was larger than the geomorphologically derived catchment scale. Subsequent partitioning of macroinvertebrate data into regions revealed a relationship between macroinvertebrate distribution and the catchment and zone scales of river system organization. Consideration of the hierarchical organization of river systems from a purely physical perspective may fail to encompass scales relevant to the biota, indicating that biological information should be included as a primary hierarchical component in multiscale stream studies.