Spatial scale, heterogeneity and functional responses

Abstract

Summary In a laboratory experiment, we studied the effect of arena size on the functional response of the mysid shrimp Neomysis integer preying on the cladoceran Polyphemus pediculus. The aim of the study was to examine mechanisms that cause the functional response to be scale‐dependent, by documenting the spatial distribution and the movement behaviour of predator and prey. The attack rate was significantly higher in large arenas, while the handling time did not differ between arena sizes. The difference in attack rate could be explained by differences in aggregative behaviour of predator and prey and in swimming activity of the predator. It is suggested that distributions of animals are often affected by the walls of the experimental arenas and that this spatial heterogeneity is scale‐dependent, which may have a considerable impact on estimates of ecological process rates. A method of correcting attack rate estimates for artefacts caused by such spatial heterogeneity is presented.