Interacting environmental gradients, trade-offs and reversals in the abundance-environment relationships of stream insects: When flow is unimportant

Abstract

Flow is often presumed to determine the distribution of stream invertebrates across stream beds. When temperatures are high, however, dissolved oxygen (DO) and its interactions with other environmental gradients may be more important. Field surveys were carried out in summer at two sites in a sand-bed stream in south-east Australia. Using quantile regression, we quantified the abundanceenvironment relationships of a caenid mayfly and an ecnomid caddisfly, and determined whether DO, fine detritus or velocity was the dominant limiting variable, and to gain insight into the causal mechanisms. Local densities of caenids were driven by food resources (detritus) at a site with a short DO gradient...