Macroinvertebrates of a beaver-altered boreal stream of Alberta, Canada, with special reference to the fauna on the dams

There were different macroinvertebrate assemblages on the face of and in beaver dams compared with beaver ponds and main stream sites. The beaver dam featured a large proportion of simuliid larvae compared with the main stream sites of this stream and with areas of other studies of beaver-altered streams. The fauna of the dams was typical of fast-flowing habitats, whereas animals of the main stream sites (including the beaver ponds) were more characteristic of slow-flowing or lentic habitats. Cluster analysis separated the dam and main stream sites for each sampling date and year of our study based on the composition of the macroinvertebrates. Although the invertebrate assemblages of the dams differed from those of the main stream sites, both habitats included similar functional feeding groups, except for a shredder found only at the dams. There are similarities between the beaver dam fauna and the faunas of debris dams, woody snags, and lake outlets. Beaver dams are important in supporting large populations of simuliids and generally in maintaining a lotic fauna in slow-moving, low-gradient boreal streams.