Concomitant Predation and Infection Processes: An Experimental Study

Abstract

SUMMARY (1) The functional response of the fish predator Brachydanio rerio HamiltonBuchanan to changes in the density of two prey species, Daphnia magna L. and the cercarial stage of the ectoparasitic digenean Transversotrema patialense (Soparkar), is shown to be of the type II form where the instantaneous predation rate is unaffected by changes in prey density. (2) A model is developed to describe this functional response, based on the concept of predator satiation. The number of prey items required to create satiation is shown to be dependent on the experimental procedures used to elicit the functional response. (3) The fish predator, Brachydanio rerio, acts in the dual role of predator/host for the cercarial stage of Transversotrema patialense. The concomitant predation and infection processes created by this ecological association are shown to be characterised by constant instantaneous predation and infection rates which appear to be unaffected by changes in prey/parasite density. (4) The infection process is unaffected by density dependent constraints over a wide range of exposure densities and the number of parasites attached per host is shown to be directly proportional to cercarial numbers. (5) Stochastic elements are shown to be important determinants in the dynamics of the infection process and overdispersion in the frequency distribution of the number of parasites attached per host is thought to be generated by heterogeneity between fish and heterogeneity in time created by changes in infective stage density. (6) The relevance of concomitant predation and infection processes to the dynamics of digenean life cycles is discussed.