Interactions between Larval Size, Microdistribution and Substrate in the Stoneflies of an Iron-Rich Stream

Two species of stoneflies, Nemurella picteti Klapalek and Leuctra nigra Olivier, were abundant in a species-poor, iron-rich stream. N. picteti has a one year life cycle. At least some L. nigra larvae take two years to develop. Larvae of both species exhibited contagious dispersion patterns throughout the year. In general, larvae were over-represented in accumulations of allochthonous plant litter on which they feed. However, the younger larvae of L. nigra were relatively more common on stony substrate. Changes in distribution and abundance of the larvae through their development were related to their food supply and to intense predation pressure in the stream.