Chaoborus Predation, Prey Vulnerability, and their Effect in Zooplankton Communities

Abstract

We investigated the effect of Chaohorus predation on a variety of zooplankton prey through the development, testing, and application of a model of prey vulnerability that predicts prey selection. This model, which is based on the swimming speed of the prey and the strike efficiency of the predator, predicts that Ceriodaphnia is 3–4 times more vulnerable to Chaoborus predation than is either Daphnia or Diaptomus. In laboratory feeding experiments, Ceriodaphnia was greatly preferred by Chaoborus over Daphnia and Diaptomus; both the order and magnitude of prey selection were accurately predicted by the prey vulnerability model. This especially large impact of Chaoborus predation on Ceriodaphnia, predicted by the model, was reflected in the community dynamics of a small pond. The seasonal peak of fourth-instar Chaoborus in this pond coincided with a sharp decline in Ceriodaphnia densities, and the subsequent decline of the predator was immediately followed by a rapid increase of this prey. A field experiment, in which Chaoborus densities were manipulated in experimental enclosures in the pond, also demonstrated the substantial impact of this predator on Ceriodaphnia. Enclosures with added Chaoborus (~1.0 larvae/L) contained 15 times fewer Ceriodaphnia and 10 times fewer Diaptomus than enclosures that lacked the predator.