A Competition Submodel for Parasites and Predators

Abstract A generalized competition model for predators or parasites was developed from data obtained from a specific parasite–host system. It was structured in three parts. The first simulates the effects of exploitation, where the number of attacks and their distribution among prey or hosts determine how many prey or hosts survive. Since the negative binomial distribution described these distributions consistently, the exploitation submodel was developed from it. The second portion of the competition model concerned interference between searching predators and parasites. Although interference is a universal phenomenon, we were able to show that its effects become important only at predator densities much higher than those that occur in nature. Thus the interference component can be essentially ignored. The third and final component concerned the outcome of competition between parasite progeny within their host. It was developed from Fujii’s competition model which allows for the simulation of both scramble and contest types of competition.These three submodels of competition were combined and coupled with a previously published model of the effects of prey density on attack. In this way the full consequences of different prey and predator densities could be simulated using a model whose constituent parts had been carefully tested for descriptive adequacy. The simulations showed the way individual predator attack, per cent predation, and progeny production were affected by different degrees of contagion in the distribution of attacks, by scramble vs. contest competition, and by the degree to which parasites could avoid hosts already attacked.