The relation of drift to benthos density and food level in an artificial stream1

The relationship between drift rates, benthos density, and food level for select taxa of stream invertebrates was studied in an artificial stream system to determine if drift is independent of or dependent on population density, and if food level affects drift rates. Two taxa were introduced in a range of densities at a single level of periphyton food, and the drift from each density was measured. Four taxa were introduced in a range of densities at low and high food levels, and the drift from each density at each food level was measured. The drift of all taxa, examined by simple linear regression analysis, at each food level was judged a density independent response to increasing population density. The drift of three taxa at a given density was significantly greater at the lower food level: it is suggested that increased activity in searching for food at the lower food level resulted in increased drift.