Prey selection by Asplanchna girodi (Rotifera): the importance of prey defence mechanisms

1. Predator (laboratory-grown Asplanchna girodi and prey (several field-collected non-carnivorous rotifer species) interactions were studied in the laboratory as a function of both predator and prey densities. The clearance rates of A, girodi decreased with increasing prey density. Predator density had no effect on the feeding of A. girodi. 2. Asplanchna girodi selectively fed on Keratella cochlearis. Its clearance rates for K. cochlearis were much higher than those for Polyarthra and Brachionus. Short-spined forms (spine length less than 25 μm) showed a significantly higher susceptibility to predation than either the non-spined or the long-spined forms. 3. Large Asplanchna individuals fed selectively on reproductive females of K. cochlearis, thereby reducing the fecundity of their prey.