Interpreting patterns of resource utilization: randomness and selectivity in pollen feeding by adult hoverflies.

Adult syrphid flies feed primarily on pollen and nectar from flowers and may be regarded as suitable models for the investigation of resource partitioning in a plant/pollinator system. The present study examines the extent to which a small group of six species are selective in their diets and investigates the role of flower colour as a means by which such selectivity may occur. Flower feeding preferences were determined by pollen analyses of gut contents and an extensive flower sampling programme was under-taken to provide information on the relative abundances of the food resources available to the insects. Flower colours were defined by their reflectance spectra, and the inherent colour preferences of the flies were determined by field experiments in which natural flowers were simulated using painted plastic discs. The results reveal that some hoverfly species are highly selective in their pollen diets, while others have a more generalist approach to their foraging. The division of flower resources by the more selective species is shown to be dependent, at least partially, on the colours of the flowers. The findings are discussed in relation to the theories of Competition and Optimal Foraging and the 'mechanistic approach' to ecology. The use of learning models is suggested as an alternative means of investigating patterns of resource use in future research.