Identifying Pollution Related Changes in Chironomid Communities as a Function of Taxonomic Rank

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Abstract
This study compares specific- and generic-level analyses of chironomid presence/absence data along a heavy-metal gradient. Eighteen binary similarity coefficients were calculated for five sampling stations from a small Ohio stream that receives an effluent containing zinc, copper, and chromium from a metal-plating industry. In general, the specific- and generic-level values were highly correlated and showed similar patterns across the 10 station comparisons. The basis for this correlation was then investigated by an assessment of both the amount (average number of species per genus) and the pattern (species to genus ratio trend) of information loss along the pollution gradient. Trends in the species to genus ratio along the gradient are viewed as indicative of the similarity of congenerics in their response to the gradient. The lack of a significant trend in the species to genus ratio in our data indicates that the agreement between specific- and generic-level analyses was due to the ability of a robust species distribution pattern to withstand a limited amount of random information loss, rather than any inherent similarity among congenerics reflected in their species to genus ratio trends. Analyses based on only a few species (e.g. abundant or indicator species) cannot afford as much information loss and must rely more heavily on similarity of congeneric species.