Arena size modulates functional responses via behavioral mechanisms

Laboratory-based functional response experiments, in which foraging rates are measured across a range of resource densities, are central for determining trophic interaction strength. Historically these experiments often are performed in arbitrarily sized arenas, with larger sized organisms generally used in larger arenas. However, arena size influences foraging rates and therefore also estimates of the functional response parameters, particularly space clearance rate (attack rate). We hypothesized that non-random movement within arenas by predators and prey may explain this effect. To test this hypothesis, we video-recorded Schizocosa ocreata wolf spiders (predators) and flightless Drosophila melanogaster prey in circular arenas of three different sizes to reveal thigmotactic behavior. We then estimated foraging rates and space clearance rates from feeding trials performed at a single, low prey density in three differently-size arenas in either annular (ring-shaped) or circular arenas. ...