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83 -" and Sedell (1981), transported benthic organic matter, periphyton and functional group composition were examined by Bruns et a1. (1983). and an interbiome comparison of stream ecosystem dynamics were made hy Minshall et al. (1983). In general, these and other studies support the predictions of the River Continuum Concept. The relative importance of each functional group to community organization was determined by examining dominance ratios (dens::y of functional group/total invertebrate density) for each group collected in four streams (orders 1, 3, 5, 7) in the western Cascade Range of Oregon (Hawkins and Sedell 1981). Shredders dominated 1010' order streams and gradually decreased in importance downstream. Collectors were relatively unimportant in upstream reaches but dominated higher order sites. Scrapers gradually increased in importance reaching lOaximum dominance in the fifth order reach and then declined in the seventh order reach. Predatc,rs exhibited rather constant dominance values between sites. Other functional groups were minor components at most sites. Similar results from Idaho, Michigan, Oregon, and Pennsylvania were obtained in an interbiome comparison of strE!am ecosystem dynamics (Minshall et a1. 1983). Four stations on streams ranging from headwaters (first and second order) to medium size streams (fifth to seventh order) wer<! examined using comparable methods. As predicted by the River Continuum Concept, shredders generally were most abundant in the headwaters and rapidly declined downstream. Collectors showed a general tendency to increase in relative abundance with distance downstream but varied with site and season. Scrapers (grazers) showed a tendency to be mo'st abundant in the lower open canopy reaches during autumn (winter in Idaho) and in the upper reaches during summer, but did not strongly follow the expected pattern. The proportion of predators in the community generally was less than that of either collectors or scrapers (grazers) and rarely exceeded 30 percent of the total community abundance. The longitudinal distribution of predators was variable with no consistent pattern among sites or seasons (Minshall et al. 19~3). Examination of macroinvertebrate functional feeding groups, periphyton, and transported and benthic organic matter by polar ordination techniques after collecting samples from the Middle Fork of the Salmon River, Idaho indicated that functional group composition changed in a curvilinear fashion along the gradient (Bruns et a1. 1'983). This represents a distinct difference from the linear pattern associated with combined organic matter compositional changes along the stream continuum. The largest portion of ecological change (about 90%) occurred within the headwater and small stream portion of the gradient and only slight. change, occurred beyond the third order. Proceeding downstrea:m, the composition vf functional groups progressively became less similar to that at a headwater site and more similar to that at a large stream site. Thus, corununity structure at a particular site was a function of its position along the environmental gradient.