An Analysis of the Components of Chaoborus Predation on Zooplankton and the Calculation of Relative Prey Vulnerabilities

Publisher Website
Google Scholar
Abstract
We formulated a model for Chaoborus predation on zooplankton and analyzed its various components for fourth—instar Chaoborus americanus and three prey species (Daphnia pulex, Bosmina longirostris, and Diaptomus pallidus). This model is based upon the encounter rates between predator and prey, the probability of a first strike by Chaoborus, and the probability of ingestion given a first strike. This latter probability is a function of the strike efficiency, contact efficiency, and second—strike probability of the predator with each prey. The strike volume of Chaoborus was variable in both size and shape for the different prey species. In each case, however, it could be closely approximated by a cylinder. This strike volume was largest for Daphnia and smallest for Bosmina. The strike efficiency of Chaoborus (probability that a strike will result in a contact) was not significantly different for the three prey types, indicating that the different evasion behaviors of the prey do not influence this parameter. The contact efficiency (probability that a contact will result in a capture) on Daphnia was significantly lower than for the other ability that a contact will result in a capture) on Daphnia was significantly lower than for the other prey; this is a function of the differing sizes and shapes of the prey. Second—strike probability (probability that if a prey is initially missed by a Chaoborus strike, it will remain in the strike volume and be attacked again) was significantly different for each of the three prey species tested, with Bosmina > Daphnia > Diaptomus. This is mainly the result of the different evasion behaviors of the prey. Our model predicts that Chaoborus is equally efficient at capturing each prey once a first strike occurs. Differential vulnerabilities of these prey to Chaoborus predation are therefore the result of differing encounter rates, which are influenced by both the swimming speeds of the prey and the strike volume of the predator.