Abstract
The spatial distribution of animals is one of the main themes of ecology since its early days. The first theory that attempted to describe these distributions based on the behaviour of individuals is that of Fretwell and Lucas (1970), who assumed that animals that compete for resources have perfect knowledge of their environment and can move freely to patches where they experience a higher resource uptake rate (the Ideal Free Distribution). Many extensions and modifications of this theory have been proposed (Tregenza 1995). The match of predictions of these models with data has so far not been impressive (Treganza 1995), while predictions vary widely from model to model, depending on their assumptions. Clearly, a systematic investigation of all factors affecting distributions would greatly advance the theory of the distribution of animals. We aim to initiate such a systematic investigation using an experimental approach, focussing the most important aspects affecting distributions, which are competition, size (or stage) structure and predation. The study system consists of the western flower thrips Frankliniella occidentalis, and its predatory mite Iphiseius degenerans. The interactions between these species are complex and well-studied; all mobile stages of the predatory mite attack young instars of the thrips, while the older instars are invulnerable. Moreover, both species thrive on plant-provided pollen; hence, the species compete for this resource. Furthermore, all mobile thrips stages can kill eggs of the predatory mite, with which they can supply their diet (Janssen et al. 2003). These interactions lead to spatial patterns in the distribution of the predators and prey. We propose a systematic investigation of the effects of competition and predation of these size structured populations on the distribution of various stages of predator and prey.
Netherlands