Community structure of caddisflies along a temperate springbrook

In an in-depth analysis of zonation patterns we examined the seasonal distr ibution of caddisfly larvae from 22 sites along the 420m length of an Appal achian springbrook. We used a Wilcoxin signed rank test to determine whethe r each species was clumped at a particular location or randomly distributed along the length of the brook. This approach permitted objective character ization of observed distribution patterns. Of the 27 species of caddisfly l arvae collected during this study, 2 had upstream distributions (Apatania b lacki and Lepidostoma frosti) and 4 had downstream distributions (Diplectro na modesta, Dolophilodes distinctus, Hydropsyche ventura and Paranyctiophyl ax nephophilus) in at least 1 season. With the exception of Parapsyche apic alis, most filtering-collector species were clustered downstream. In 2 out of 4 seasons, trichopteran species richness peaked at an intermediate dista nce along the springbrook. Evenness of the trichopteran community increased downstream in September, December, and June, when Apatania blacki dominate d the trichopteran community at the upstream sites. Spring restricted speci es (Apatania blacki and Lepidostoma frosti) ranged farther downstream in Se ptember and December than in March or June. The upper distributions of down stream species fluctuated from season to season, but the changes were not c onsistent among species. The results illustrate that zonation patterns in s pringbrooks are not fixed but have a strong seasonal component.