Predicting the Colonization Cycle of Aquatic Invertebrates

The components of the colonization cycle for aquatic invertebrates (drift, upstream movement within the stream, and female flight direction) were quantified for a small Pennsylvania stream. Diel periodicities were evident for both aquatic and terrestrial drift. A regression predicted a linear relation between the proportion of benthos in the drift and the degree of upstream female flight. Accordingly, insects commonly occurring in the drift (Chironomidae, Baetis spp., Ephemerella invaria) showed significant upstream flight of females, whereas those rarely found in the drift (Glossosoma intermedium and G. nigrior, Psychodidae, Hydroptila spp. and Ochrotrichia wojcickyi, Sialis spp.) did not show significant upstream flight of females. Organisms without a winged adult stage (Gammarus minus, Turbellaria) showed a greater degree of upstream movement in the stream. Upstream movement in the stream compensated for only 2.6% of the total aquatic drift in July.