Data from "Prey:predator ratio dependence in the functional response of a freshwater amphipod

1. First known for their shredding activity, freshwater amphipods also behave as active predators with consequences for prey population regulation and amphipod coexistence in the context of biological invasions.2. A way to quantify predation is to determine the average consumption rate per predator, also known as its functional response (FR).3. Although amphipods are gregarious and can display social interactions that can alter per capita consumption rates, previous studies using the FR approach to investigate amphipod predation ignored such potential mutual interference because they did not consider variations in predator density.4. We investigated the FR of <i>Echinogammarus berilloni </i>feeding on dipteran larvae with joint variations in prey and predator densities. This bivariate experimental design allowed us to estimate interference and to compare the fits of the three main classes of theoretical FR models, in which the predation rate is a function of prey density alone (prey-dependent models), of both prey and predator densities (predator-dependent models) or of the prey-to-predator ratio (ratio- dependent models).5. The Arditi–Ginzburg ratio-dependent FR model provided the best representation of the FR of E. berilloni, whose predation rate showed a decelerating rise to a horizontal asymptote as prey abundance increased.6. Ratio dependence means that mutual interference between amphipods leads to prey sharing. Mutual interference is likely to vary between amphipod species, depending on their level of aggressiveness.~~~~~~~~~~~~~~~~~~~~~~~~~~~~Non-integer values refer to partial consumption.Chaoborus larvae are quite homogeneous in size and length so it is relatively easy to visually assess partial consumption.The value of 2.75 means that the gammarid consumed entirely two larvae and the three quarters of another one.1. 淡水端足类（amphipods）最初以其碎食行为为人所知，同时它们也是活跃的捕食者，这会对生物入侵背景下的猎物种群调控以及端足类物种共存产生影响。 2. 量化捕食行为的一种方法是测定每头捕食者的平均摄食率，这也被称为其功能响应（functional response，FR）。 3. 尽管端足类具有群居习性，且会展现出会改变个体摄食率的社会互动，但此前采用功能响应（FR）方法研究端足类捕食行为的研究均忽略了这类潜在的相互干扰——这是因为它们未考虑捕食者密度的变化。 4. 我们研究了贝氏棘钩虾（Echinogammarus berilloni）在猎物与捕食者密度联合变化条件下取食双翅目幼虫时的功能响应（FR）。该双因素实验设计使得我们能够估算捕食者间的相互干扰，并对比三类主要理论功能响应模型的拟合效果：这三类模型分别将捕食率仅作为猎物密度的函数（猎物依赖型模型）、同时作为猎物与捕食者密度的函数（捕食者依赖型模型），或是作为猎物与捕食者比例的函数（比例依赖型模型）。 5. 阿尔迪蒂-金茨堡（Arditi–Ginzburg）比例依赖型功能响应模型最贴合贝氏棘钩虾的功能响应特征：随着猎物丰度提升，其捕食率呈现减速上升并最终趋于水平渐近线的趋势。 6. 比例依赖型功能响应意味着端足类之间的相互干扰会导致猎物资源的共享。不同端足类物种间的相互干扰程度可能存在差异，这取决于它们的攻击性水平。 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~非整数数值代表部分摄食。幽蚊（Chaoborus）幼虫的体型与体长均较为均一，因此通过视觉评估其部分摄食情况相对容易。数值2.75表示该钩虾完全取食了2头幼虫，并取食了另外1头幼虫的四分之三。