THE CONSTANCY OF INVERTEBRATE ASSEMBLAGES IN SOFT-WATER STREAMS - IMPLICATIONS FOR THE PREDICTION AND DETECTION OF ENVIRONMENTAL-CHANGE

Invertebrates were sampled annually for 5 yr in the riffles and margins of 18 upland streams. Constancy (persistence) of the invertebrate faunas and their relationships to environmental variables were examined by comparing stream ordination, classification, indicator species and methods from multiple discriminant analysis in different years. Analyses relied principally on the presence or absence of taxa. Classification and ordination of unmanipulated streams were highly consistent in different years. In general, discriminant models derived in one year were successful in predicting faunal groups in other years. Three streams limed to counter acidity did not show any clear changes in persistence as a result, and exhibited only a small proportion of the faunal change expected from the discriminant models. In terms of relative abundance, persistence was lower in marginal samples than in riffles. There were also variations across streams in persistence from year to year, and some evidence of long-term change in the invertebrate faunas. Decreasing persistence in riffles was most strongly related to increasing amounts of vegetation in the stream margins. -from Authors