Data from: Functional responses modified by predator density

Realistic functional responses are required for accurate model predictions at the community level. However, controversy remains regarding which types of dependencies need to be included in functional response models. Several studies have shown an effect of very high predator densities on per capita predation rates, but it is unclear whether this predator dependence is also important at low predator densities. We fit integrated functional response models to predation data from 4-h experiments where we had varied both predator and prey densities. Using an information theoretic approach we show that the best-fit model includes moderate predator dependence, which was equally strong even at low predator densities. The best fits of Beddington–DeAngelis and Arditi–Akcakaya functional responses were closely followed by the fit of the Arditi–Ginzburg model. A Holling type III functional response did not describe the data well. In addition, independent behavioral observations revealed high encounter rates between predators. We quantified the number of encounters between predators and the time the focal predator spent interacting with other individuals per encounter. This time ‘‘wasted’’ on conspecifics reduced the total time available for foraging and may therefore account for lower predation rates at higher predator densities. Our findings imply that ecological theory needs to take realistic levels of predator dependence into account.

要实现群落水平的精准模型预测，必须采用符合现实场景的功能响应（functional response）。然而，学界对于功能响应模型中需纳入哪些类型的依存关系仍存在争议。已有多项研究证实，极高的捕食者密度会对单位捕食者捕食率产生影响，但目前尚不明确这种捕食者依存关系在低捕食者密度下是否同样具有重要意义。我们针对4小时捕食实验中获取的数据拟合了整合功能响应模型（integrated functional response models），实验过程中同时调控了捕食者与猎物的密度。借助信息论方法（information theoretic approach）开展分析，结果显示最优拟合模型包含了适度的捕食者依存关系，且即使在低捕食者密度下，该依存关系的强度也未出现明显减弱。贝丁顿-德安杰利斯（Beddington–DeAngelis）与阿尔迪蒂-阿克卡亚（Arditi–Akcakaya）功能响应模型的拟合效果紧随其后，拟合表现仅次于前者的是阿尔迪蒂-金兹堡（Arditi–Ginzburg）模型。霍林III型（Holling type III）功能响应则无法较好地适配实验数据。此外，独立行为观测结果显示，捕食者之间的相遇频次较高。我们量化了捕食者间的相遇次数，以及目标捕食者每次相遇时与其他同种个体互动所耗费的时长。这种被浪费在同类身上的时间，会压缩可用于觅食的总时长，因此或可解释高捕食者密度下捕食率偏低的现象。我们的研究结果表明，生态学理论需要将符合现实水平的捕食者依存关系纳入考量范畴。