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Abstract

The foraging ecology of six trichopteran scrapers with similar life cycles was examined. Gut contents from the later stages were analyzed and compared during 1986 and 1987 along the lower 2 km of the stream. The percent areas of 9 gut content components were quantified using image analysis. Seasonal variability in periphyton composition was reflected in the larval gut contents. Diatom maxima in spring and autumn, and a cyanobacteria maximum in the summer, were especially condspicuous. A multifactorial ANOVA showed significant differences (p <0,001) between the utilizationintensities of several food components by the species considered, even though their microhabitats and food resources distinctly overlapped. The comparison of mean values (± 95% CL) showed increased percent areas of diatoms in Drusus annulatus, Tinodes rostocki and Micrasema longulum, increased percent areas of cyanobacteria in Apatania fimbriata and D. annulatus, and decreased percent areas of algae, but increased percent areas of detritus, in Agapetus fuscipes and Silo pallipes. Guts of A. fimbriata and D. annulatus contained algae in similar proportion to the local periphyton. T. rostocki and M. longulum contained higher proportions of diatoms. A cluster analysis revealed three species groupings. A. fuscipes and S. pallipes showed the most distinct trophic niche overlap, followed by A. fimbriata and D. annulatus. At a lower similarity level T. rostocki and M. longulum were combined within one group. The results of food choice experiments offering different food qualities on membrane-filters correlated with the data from the gut analyzes. D. annulatus and M. longulum larvae mostly frequented filters with periphyton, and had the highest algal proportions in their guts. Filters with detritus were frequented mostly by A. fuscipes and S. palipes, and their guts contained the highest proportions of detritus. Different foraging strategies seemed to be apparent among the six species, reducing the competition for high quality food resources. The full paper will be published elsewhere.