Distribution of puimonate snails in the New River of Virginia and North Carolina, U.S.A.: interaction between alkalinity and stream drainage area

SUMMARY. The distribution and abundance of five species of pulmonate snails over 87 sites in the New River seem to be related to two variables, alkalinity and drainage area of the stream. The snails were generally found in the more alkaline streams regardless of stream drainage area and in the larger streams regardless of alkalinity. Considering only the 26 sites where at least one species of the five pulmonates occurred, rank snail abundance is significantly correlated with rank alkalinity, rank drainage area, and the alkalinity/area interaction. But the correlations between abundance and both alkalinity and drainage area drop to low levels when interaction is partialled out, while the correlation between abundance and interaction remains high upon partialling out alkalinity or area. This suggests that the apparent correlation between puimonate abundance and alkalinity is secondary and that neither alkalinity nor water chemistry variables correlated with it directly limit the distribution and abundance of pulmonates in the New River. Both alkalinity and stream drainage area may influence the abundance of pulmonate food.