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

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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.