Multiple mechanisms of species coexistence as a basis for biodiversity maintenance and ecosystem functioning

解释物种共存的机制对于理解在地方尺度上维持生物多样性以及生物多样性对生态系统功能的影响至关重要。在这个子项目中，我们将分析耶拿实验植物群落中种群动态的时间进程，以测试物种共存的多种机制。(1)我们将应用竞争网络理论，通过分析从成对竞争矩阵预测物种竞争排名的可能性是否随着植物多样性的增加而降低，并通过评估它与所涉及物种的功能特征的关系。(2)基于最近的共存理论，我们将测试种群增长的负频率依赖性，作为稳定生态位差异的指标。我们将探索与稳定机制相关的各种预测因子的单一和累积效应，例如作为资源利用生态位互补性指标的物种之间的功能特征差异，天敌(草食动物、真菌病原体)的频率依赖攻击和物种对环境变化的特定反应，以及种子和幼苗人口密度得出的相对适合度差异的重要性。(3)我们将探索竞争网络中的不可传递性和物种丰富度的平均等级变化对多种生态系统功能及其时间变异性的影响。(4)最后，我们将研究植物-土壤反馈如何影响植物群落的植物性能和抗入侵能力，通过参与新的Delt-BEF，在长期主要实验的群落中，分别以低性能和高性能物种为重点进行植物计量仪研究，并研究Delt-BEF不同处理中自发定居物种的组成。综上所述，对种群动态的长时间序列的综合分析，以及与可能解释物种共存的不同机制相关的独特数据的汇编，以及在该子项目中获得的新的实验数据，将促进我们对本地物种组合中生物多样性的维持及其对生态系统功能的影响的理解。

Explaining the mechanisms underlying species coexistence is fundamental for understanding the maintenance of biodiversity at local scale and the effects of biodiversity on ecosystem functioning. In this subproject we will analyse the time course of population dynamics in the plant communities of the Jena Experiment to test for multiple mechanisms of species coexistence.(1) We will apply competitive network theory by analysing whether the possibility to predict species` competitive ranks from pair-wise competition matrices decreases with increasing plant diversity and by evaluating how it relates to the functional traits of the involved species.(2) Based on recent coexistence theory, we will test for negative frequency-dependence of population growth as an indicator of stabilizing niche differences. We will explore the single and cumulative effects of various predictors related to stabilizing mechanisms such as functional trait differences among species as indicator for niche complementarity in resource use, frequency-dependent attack of natural enemies (herbivores, fungal pathogens) and species-specific responses to environmental variation as well as the importance of relative fitness differences derived from seed and seedling demographic rates.(3) We will explore the consequences of intransitivity in competition networks and mean rank shifts in species abundances for multiple ecosystem functions and their temporal variability.(4) Finally, we will study how plant-soil feedback affects plant performance and invasion resistance of the plant communities by contributing to the new DeLT-BEF with a phytometer study focusing on species with low and high performance, respectively, in the communities of the long-term main experiment and studying the composition of the spontaneously colonizing species in the different treatments of the DeLT-BEF.In summary, the synthesis analyses of the long time series of population dynamics, together with a unique compilation of data related to different mechanisms potentially explaining species coexistence and the new experimental data obtained in this subproject, will advance our understanding of the maintenance of biodiversity in local species assemblages and its consequences for ecosystem functioning.