The Constancy of Invertebrate Assemblages in Soft-Water Streams: Implications for the Prediction and Detection of Environmental Change

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Abstract
Invertebrates were sampled annually for 5 years in the riffles and margins of eighteen upland streams. Constancy (persistence) of the invertebrate faunas and their relationships to environmental variables were examined by comparing stream ordination, classification, indicator species and models from multiple discriminant analysis in different years. These analyses relied principally on the presence or absence of taxa. Constancy incorporating information on relative abundances was assessed by Spearman rank correlation. 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. We discuss the relevance of these observations to the prediction and detection of environmental change. We also speculate on the factors affecting persistence of invertebrate faunas in different stream habitats.

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