Biodiversity of Minnesota caddisflies (Insecta: Trichoptera)

Over 300,000 caddisfly specimens were examined based on 317 light trap samples collected during 1999–2001, and from museum records. Two hundred-eighty-four caddisfly species were determined to occur in Minnesota, representing 20 families and 74 genera. The relative occurrence in different regions, habitat types, and levels of upstream disturbance is documented for each species.; Detrended Correspondence Analysis and a UPGMA dendogram of caddisfly relative abundance data from 58 Minnesota watersheds delineated five regions of caddisfly biodiversity. Caddisfly species richness and diversity were significantly highest in the Lake Superior and Northern regions, lowest in the Northwestern and Southern regions, and intermediate in the Southeastern region. These determined regions had nearly double the classification strength of a priori ecological regions or watersheds in partitioning the natural variation of the caddisfly fauna. Classification strength also decreased with increasing spatial scale and decreasing taxonomic resolution.; Canonical Correspondence Analysis found that temperature, percentage of disturbed habitat, and stream gradient were related to caddisfly species composition, although the correlation between temperature and disturbed habitat made determination of the relative importance of those variables difficult. Caddisfly species richness correlated negatively with percentage of disturbed upstream habitat for small and medium-sized streams in the Northern, Northwestern, and Southern regions.; Change in the composition of trophic feeding groups based on habitat type generally followed a pattern predicted by the river continuum concept in the Lake Superior, Northern, and Southeastern regions, whereas fine particle filtering collectors dominated all sizes of lakes and streams in the Northwestern and Southern regions. Binomial regression analysis determined three fine particle filtering collectors as indicators of habitat disturbance—particularly that of lakes and small streams—independent of other environmental variables.; Although the absence of historical data makes it difficult to separate the relative importance of natural and anthropogenic factors, loss of caddisfly biodiversity and homogenization of feeding ecology has probably occurred in at least the Northwestern and Southern regions due to human disturbance. With baseline data now in place, potential future changes can be evaluated with greater confidence.