Longitudinal and seasonal changes in functional organization of macroinvertebrate communities in four Oregon streams

Relative numerical dominance and densities of invertebrate functional feeding groupsare compared with longitudinal and seasonal changes in food resources in a Cascade Range streamsystem in Oregon. We also compare our data with hypothetical predictions of the River Continuummodel.
We found that both relative abundances and densities of functional groups fit qualitative charac-terization of stream reaches and the River Continuum model: Shredders dominated upper shadedreaches; scrapers were most important in intermediate-sized sections; collectors increased in impor-tance progressively downstream: predators were nearly constant in relative a7undan,:e at all sections:other functional groups were either rare or only locally abundant. Seasonal shifts also occurred butwere not as dramatic as longitudinal differences.
Correlation analyses between quantitative measures of food sources and functional group abun-dance were usually significant. Lack of significance for some correlations is likely due to inaccuratecharacterization of food availability, but small sample size and improper classification of species'feeding behavior also may be important. In addition, invertebrate densities and food standing cropare static parameters and only approximately reflect the dynamics of consumer production and foodavailability.
Key words: community organization: distribution: functional feeding groups: ma•roinverte-brutes: River Continuum: streams: trophic ecology.