Data from: Disentangling demographic co-effects of predation and pollution on population dynamics

In nature species react to a variety of endogenous and exogenous ecological factors. Understanding the mechanisms by which these factors interact and drive population dynamics is a need for understanding and managing ecosystems. In this study we assess, using laboratory experiments, the effects that the combinations of two exogenous factors exert on the endogenous structure of the population dynamics of a size-structured population of Daphnia. One exogenous factor was size-selective predation, which was applied on experimental populations through simulating: (a) selective predation on small prey, (b) selective predation on large prey and (c) non-selective predation. The second exogenous factor was pesticide exposure, applied experimentally in a quasi-continuous regime. Our analysis combined theoretical models and statistical testing of experimental data for analyzing how the density dependence structure of the population dynamics was shifted by the different exogenous factors. Our results showed that pesticide exposure interacted with the mode of predation in determining the endogenous dynamics. Populations exposed to the pesticide and to either selective predation on newborns or selective predation on adults exhibited marked nonlinear effects of pesticide exposure. However, the specific mechanisms behind such nonlinear effects were dependent on the mode of size-selectivity. In populations under non-selective predation the pesticide exposure exerted a weak lateral effect. The ways in which endogenous process and exogenous factors may interact determine population dynamics. Increases in equilibrium density results in higher variance of population fluctuations but do not modify the stability properties of the system, while changes in the maximum growth rate induce changes in the dynamic regimes and stability properties of the population. Future consideration for research includes the consequences of the seasonal variation in the composition and activity of the predator assembly in interaction with the seasonal variation in exposure to agrochemicals on freshwater population dynamics.

在自然界中，物种会对多种内源性与外源性生态因子产生响应。阐明此类因子相互作用并驱动种群动态的机制，是理解与管理生态系统的核心前提。本研究通过室内实验，探究两种外源性因子的组合对水蚤（Daphnia）体型结构化种群的种群动态内源性调控结构的影响。第一种外源性因子为体型选择性捕食，实验中通过以下三种模拟方式施加于受试种群：(a) 小型猎物选择性捕食、(b) 大型猎物选择性捕食，以及(c) 非选择性捕食。第二种外源性因子为农药暴露，实验中采用准连续暴露方案进行施加。本研究结合理论模型与实验数据的统计检验，分析不同外源性因子如何改变种群动态的密度依赖结构。研究结果表明，农药暴露与捕食模式在调控种群内源性动态过程中存在显著交互作用。同时暴露于农药且经历幼体选择性捕食或成体选择性捕食的受试种群，表现出显著的农药暴露非线性效应。但此类非线性效应背后的具体作用机制，取决于体型选择性捕食的模式。在施加非选择性捕食的受试种群中，农药暴露仅呈现出微弱的侧向效应。内源性过程与外源性因子的潜在相互作用方式，决定了种群动态的整体走向。平衡密度的提升会加剧种群波动的方差，但不会改变系统的稳定性特征；而最大增长率的变化则会改变种群的动态模式与稳定性属性。未来研究可进一步探讨捕食者群落组成与活性的季节变化，结合农用化学品暴露的季节变异，对淡水种群动态产生的综合效应。