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. ...基于实验室的功能反应实验（functional response experiment）通过在一系列资源密度梯度下测定捕食速率，是确定营养相互作用强度的核心研究手段。既往此类实验多在规格任意的实验饲养区（arena）中开展，通常体型更大的受试生物会被置于体积更大的实验饲养区中。然而，实验饲养区的规格会影响捕食速率，进而干扰功能反应参数的估算结果，尤以空间清除率（space clearance rate，即攻击率）为甚。我们提出假说：捕食者与猎物在实验饲养区内的非随机移动或许可以解释这一效应。为验证该假说，我们对三种不同规格圆形实验饲养区内的饰纹狼蛛（Schizocosa ocreata，捕食者）与无翅黑腹果蝇（Drosophila melanogaster，猎物）进行录像，以观测其趋触性行为（thigmotactic behavior）。随后，我们在三种不同规格的环形（ring-shaped）或圆形实验饲养区中，以单一低猎物密度开展摄食实验，据此估算捕食速率与空间清除率。……