Analysing size-density relationships of aquatic communities in response to strength of predator-prey interactions and resource subsidy

能量等效假说（假设每个物种从环境中提取的能量大致相同）框架内的大小-密度关系可以成为生态系统生态学的核心概念，既可以理解群落结构的基线期望，也可以评估自上而下和自下而上的过程和生态系统服务的影响。然而，尽管有强大的理论基础，能量等效假说的经验证据在很大程度上是缺失的。我们的建议旨在利用欧洲监测项目（欧盟水框架指令）和几个湖泊特定研究项目获得的湖泊鱼类及其猎物的现有尺寸数据，来测试捕食者-猎物相互作用和资源补贴是否会像能量等效假设预测的那样改变鱼类的尺寸-密度关系。对于这种方法，我们可以使用来自近400个湖泊的标准化采样数据，这将为假设检验提供足够的统计能力。然而，在将这些数据与理论预测进行比较之前，必须对根据鱼类监测数据计算大小-密度关系的最佳统计方法进行验证和验证。因此，该提案解决了计算大小-密度关系的方法的系统比较，以及基于不同采样年份的同一湖泊结果的比较。在开发出优越的统计方法后，它将用于测试大小-密度关系指数是否以可预测的方式变化，以响应加强的自上而下的控制或响应陆地对湖泊生态系统的补贴。从长远来看，这种方法可能有助于从相互作用的种群的大小分布来评估生态系统过程的强度。

Size-density relationships within the framework of the Energetic Equivalence Hypothesis (which assumes that each species extracts about the same amount of energy from the environment) can be a central concept in ecosystem ecology both for understanding baseline expectations of community structure and for evaluating the effect of top-down and bottom-up processes and ecosystem services. However, despite strong theoretical foundations, empirical evidence for the Energetic Equivalence Hypothesis is largely missing. Our proposal aims to use existing size data of fish and their prey in lakes obtained for European monitoring programs (EU Water Framework Directive) and from several lake-specific research programs to test whether predator-prey interactions and resource subsidy modify the size-density relationships of fish as predicted by the Energetic Equivalence Hypothesis. For this approach, we can use data from almost 400 lakes sampled in a standardized way which will generate sufficient statistical power for hypothesis-testing. However, before these data can be compared with theoretical predictions, a validation and verification of the optimum statistical approach to calculate size-density relationships from fish monitoring data has to be conducted. Therefore, the proposal addresses a systematic comparison of methods to calculate size-density relationships, and a comparison of results from the same lakes, but based on differing sampling gears. After the superior statistical approach is developed, it will be used to test whether the exponents of size-density relationships shift in a predictable way in response to enhanced top-down control or in response to terrestrial subsidy to lake ecosystems. In the long-term, this approach may help evaluating the strength of ecosystem processes from the size distribution of their interacting populations.