A capture-rate model of net-spinning caddisfly communities.

Empirical research suggests that net-spinning caddisflies require two basic resources, suspended particulate foods, and the currents which deliver them. I present a theoretical model of caddisfly communities based on quantitative differences in the capture rate produced by different catchnet designs. It assumes that catchnet architecture reflects a tradeoff between water filtration rate (flux through the net) and capture efficiency (the proportion of suspended items retained), and that the marginal resource concentration required by species with different catchnet morphologies should reflect the product of these parameters. The model hypothesizes a) that downstream changes in the physical morphology of the stream channel cause a shift in the relative importance of population limitations imposed by food and current-substrate availability, b) that the interaction of these physical changes with the filtering biota results in a seston resource gradient, and c) that the distribution of each taxon along this resource gradient reflects a marginal resource requirement determined by the functional morphology of its catchnet.