The predatory behavior of Mesocyclops edax: Predator preferences, prey defenses, and starvation-induced changes1

The predatory behavior of field-collected Mesocyclops edax on four different kinds of prey was compared under similar and different predator starvation regimes. Unstarved Mesocyclaps did not consume either the ciliate Rhabdostyla or the cladoceran Bosmina. Increasing starvation in the predator increased the probability of ingestion after encounter for both of these prey. The rotifer Asplanchna and the nauplii of the copepod Diaptomus were consumed by starved and unstarved Mesocyclops. The probability of ingestion after encounter increased with increasing predator starvation for Asplanchna, but not for nauplii. Both behavioral and morphological characteristics of the prey were important in regulating the predator’s ability to capture and ingest the prey and in determining the time and energy which the predator had to invest to receive its nutritional rewards. Although much emphasis has been placed on the importance of invertebrate predation in structuring zooplankton communities, hunger-the driving force behind predation-has not been adequately considered. Starvation will increase predation rates in various aquatic invertebrate predators including rotifers (Gilbert in press) and copepods (Brand1 and Fernando 1974,1975a,b; Jamieson in press). However, little is known about how starvation influences predation rates and the selectivity of zooplankton predators for different types of prey. The experiments reported here show that starvation in the predatory copepod Mesocyclops edax Forbes will induce complex behavioral changes that lead to a shift in prey preferences. I thank J. J. Gilbert, W. C. Kerfoot, J. Jacobs, and two referees for helpful suggestions.