Effects of canopy, substrate composition, and gradient on the structure of macroinvertebrate communities in Cascade Range streams of Oregon

The relative importance of surrounding riparian vegetation and substrate compositionon invertebrate community structure was investigated in six streams in Oregon, USA. We found thatcanopy type was more important than substrate character in influencing total abundance and guildstructure. Streams without shading had higher abundances of invertebrates than did shaded streams.Most guilds were influenced by qualitative differences in food availability rather than quantity of foodor substrate composition. Open streams had higher abundances in the collector—gatherer, filter feeder,herbivore shredder and piercer, and predator guilds. Contrary to expectations, shredders were nomore abundant in shaded streams than in streams lacking a riparian canopy. Scraper density wasinversely related to standing crop of aufwuchs, but biomass was positively correlated with quantityof aufwuchs. Examination of dominance-diversity curves showed that both canopy and substrateinfluenced ranked abundances of taxa, but neither canopy nor substrate strongly influenced numberof taxa. Differences in community structure were not always revealed by analysis of community-levelproperties, although differences in both the absolute and relative abundances of individual taxa wereobserved.
Key words: community structure; functional groups; guilds; land use practices; macroinverte-brates; Oregon; riparian canopy; streams; substrate.