Direct observations of the mechanisms of interference between Daphnia and Keratella cochlearis1

Direct observation was used to describe and quantify four types of interaction between Daphnia (D. pulex, D. rosea, D. galeata mendotae, D. ambigua, and D. magna) and the rotifer, Keratella cochlearis f. tecta. The types of encounter differed primarily in duration, in the appendage movements elicited in Daphnia, and in the damage to Keratella. Egg‐carrying rotifers were just as susceptible to damage by Daphnia as nonovigerous rotifers. The frequency of interactions lethal to Keratella increased with increasing body size of Daphnia and decreased at algal concentrations above the incipient limiting concentration. By combining direct observations of the proportions of Keratella killed with measurements of Keratella‐based clearance rates by Daphnia, the actual pumping rate of Daphnia could be estimated.