A Unified Model of the Functional Response of Predators and Parasitoids

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Abstract
The classicial disc model for the type II functional response is modified to describe the parasitoids that are able to discriminate between healthy and parasitized hosts: different handling times are assumed for each type of host (Th and Tp). The model is integrated in time to account for the decrease of healthy hosts and increase of parasitized hosts. Rogers'' (1972b) random predator equation and random parasite equation (which is only valid for non-discriminating parasitoids) appear as the special cases Tp = O and Tp = Th. Thus, the new model unifies the treatment of predators and parasitoids. The influence of the parameters on the searching efficiency (and on other quantities) is studied. Increasing the parasitoid density may either increase or decrease the searching efficiency. The model also applies to imperfectly discriminating parasitoids. It can easily be extended to type III or dome-shaped functional responses.