Data from: 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. Annular arenas mitigated the effects of predator and
prey aggregation and thus controlled the experienced prey density near
arena edges. Unlike the circular arenas, annular arenas produced similar
foraging rates and space clearance rate estimates across arena sizes,
confirming that it is the increased density of prey along edges that
generates the previously observed arena size effect. Our results provide a
key insight into how animal behavior and experimental design must be
considered for the accurate interpretation of foraging rates, both when
considering standalone functional responses and when making comparisons
across experiments.

基于实验室的功能反应（functional response）实验通过测定不同资源密度下的觅食速率，是明确营养相互作用强度的核心手段。过往此类实验通常在任意规格的实验 arena（arena）中开展，且体型更大的实验生物通常会被放置于更大的实验 arena 中。然而，实验 arena 的规格会影响觅食速率，进而干扰功能反应参数的估算结果，尤其是空间清除率（攻击率，attack rate）。我们提出假说：捕食者与猎物在实验 arena 内的非随机移动，或可解释这一现象。为验证该假说，我们借助三种不同规格的圆形实验 arena，对捕食者毛刷狼蛛（Schizocosa ocreata）以及无翅黑腹果蝇（Drosophila melanogaster，猎物）进行录像，以观测其趋触性行为（thigmotaxis）。随后，我们通过在三种不同规格的环形（annular，环状）或圆形实验 arena 中、以单一低猎物密度开展的喂食实验，估算了觅食速率与空间清除率。环形实验 arena 可缓解捕食者与猎物的聚集效应，从而控制了实验 arena 边缘区域的实际遭遇猎物密度。与圆形实验 arena 不同，环形实验 arena 在不同规格下均能得到相近的觅食速率与空间清除率估算结果，证实了此前观测到的实验 arena 规格效应，正是由边缘区域猎物密度升高所引发的。本研究结果为：无论是单独解读功能反应实验结果，还是开展跨实验比较，如何结合动物行为特征与实验设计来准确解析觅食速率，均提供了关键的科学见解。