A trait-based approach to plant metacommunities

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The objective of SP 1 is to mechanistically understand long-term real-world plant metacommunity processes in changing environments. For this we will embrace a process-based metacommunity framework, which requires to empirically quantify (i) density-independent responses, (ii) density-dependent pairwise species interactions (iii) dispersal kernels, and (iv) immigration and emigration over time for all species co-occurring in a real community. We will formalise this framework in trait-based simulation models that can accommodate the empirical real-world data, explore coexistence mechanisms and spatial processes by varying process parameters, and make predictions about the long-term metacommunity development with changing environmental conditions. Our model system comprises the Spiekeroog salt marsh system with 12 artificial islands. This experiment runs since 2014. The functional composition of salt marsh communities is strongly structured by deterministic environmental gradients of diurnal inundation, ground water levels, and salinity along the elevation gradient from the pioneer zone to the higher saltmarsh. Additionally, the salt marsh ecosystem is dominated by pulse disturbances, such as storm surges and soil salinity enhancing heat waves. In the future, sea level rise may require the species to migrate inland. In many areas, only vertical accretion by sedimentation will ensure the long-term stability and survival of salt marshes. Finally, habitat isolation and heterotrophic consumers as next trophic level influence metacommunity behavior. These interacting processes may prevent equilibrium, niche-based community assembly.The second phase of SP1 consists of the following workpackages, each integrating modelling and empirical approaches: WP0 will establish an individual-based model based on empirical observations. Based on this tool, WP1 will investigate competition mechanisms in response to multiple stressors. We assume that the observed peak in species richness at the centre of the environmental gradient is due to niche separation. WP2 will investigate transient metacommunity dynamics when environmental gradients shift in space and time. Pulse disturbances driving transient community dynamics are storm surges and heat waves increasing soil salinity stress. WP3 will analyse niche construction by plant traits that enhance sedimentation. Niche construction may counteract effects of pulse disturbances and facilitate niche-based plant community assemblies. Finally, WP4 will model and analyse plant-herbivore interactions. SP1 will interact with all other sub-projects. In particular with SP2 (root–fungal interactions), SP3 (plant-herbivore interactions), SP4, SP5 (resilience to pulse disturbances), SP6 (passive dispersal), SP7 (meta food web model), SP1 and SP8 (extension of spatial scale), SP10 (theory), and SPZ (data collection, data base, permit administration).