Influences on the drift patterns of aquatic invertebrates.

Abstract

The purpose of our study was to determine whether invertebrates in the Maple River respond to predators by altering their drift activity. Two sites were chosen based on the density of predators at each site. One site has a high predator population of trout, while the second site has a low predator population of trout. We expected that invertebrates at the site with predators would exhibit nocturnal drift periodicity because they would be attempting to avoid predation. This strong pattern of nocturnal drift was not expected in the second branch where the waters are trout free. We also expected to see a greater number of large invertebrates drifting at night, as previous studies have shown. ... While our research added support to results of previous studies, we also uncovered many discrepancies that should be explored further. The drift patterns that we found in the Maple River did not correspond exactly to previous results and our total drift densities were much lower than those collected in other studies. This could be due in large part to the unseasonably cold spring we have experienced. Perhaps research done later in the summer would reveal results more similar to those of previous studies.