Production Rate, Population Density, and Drift of a Stream Invertebrate

Abstract

Production rates of the stream mayfly, Baetis vagans McDunnough (Ephemeroptera: Baetidae), were estimated by two different methods, compared, and related to population density and drift rate. In the year of study, this mayfly had two summer generations and one winter generation. The two production rate methods yielded estimates of 9.1 and 12.6 g/m 2 year as the sum of the three generations, although both estimates were minimal. Production rates for the summer generations were higher than for the winter generation, although winter production was still at a significant level. The summer generations drifted in large quantities, up to about 22 g/day, but the winter generation appeared to drift little, if any, until near the end of the generation in early spring. The relation between annual production rate and mean population density, or turnover ratio, was 9.7, or 3.2 times the number of generations.