Models of Interference and Their Consequences for the Spatial Distribution of Ideal and Free Predators

Abstract

1. In order to predict the spatial distribution of 'ideal' and 'free' predators, one needs to know how food intake rate of an individual predator is related to characteristics of the population of the prey as well as the predators themselves. 2. Surprisingly, a systematic theoretical investigation of models for the basic case, where both prey and predators are best characterized by their 'standing stock' density, is lacking. In these models intake rate is supposed to decrease with increasing predator density as a result of interference among predators, instead of immediate consumption of the prey. 3. This paper compares the various ways applied so far of incorporating interference in Holling's functional response model. It is shown that the different models of interference result in qualitatively different predictions for 'ideal' and 'free' predators on: (i) the form of the aggregative response; (ii) the trajectory of the aggregative response as prey is depleted; and (iii) the change in the aggregative response following an influx of predators. This sheds doubt on the general relevance of any one of these models, particularly if the mathematical formulation of interference is phenomenological and merely based on convention, instead of being derived from the underlying mechanism of interactions between predators. 4. Our results underline the need for detailed knowledge about the components of the predation process in order to arrive at predictions for a specific case.