HEDGE 2- From land management through habitat heterogeneity to biodiversity in grassland ecosystems: A combined theoretical, experimental, and observational study

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Spatial heterogeneity in habitat conditions is a main factor affecting biodiversity but has rarely been studied in the Biodiversity Exploratories. We attempt to fill this gap by integrating theoretical, experimental, and observational studies focusing on the mechanisms by which heterogeneity in land management and heterogeneity caused by land use affect grassland diversity. A fundamental element of our project is the idea that habitat heterogeneity may have both positive and negative effects on species diversity due to an inherent trade-off between the degree of habitat heterogeneity and the amount of effective area available for individual species in the community (AHTO-area-heterogeneity trade-off). In Phase 1, we used analytical models to investigate general properties and consequences of the AHTO with emphasis on the relaxation of simplifying assumptions made in previous formulations of this trade-off. In parallel, we established a unique experimental setup for testing predictions generated by our models under highly controlled conditions. In Phase 2, we will extend our work in three main directions. 1) We will extend our models both up (by expanding our local community model into a metacommunity framework) and down (by explicitly modeling effects of competition for soil and light resources on individual plants). The upscaling element will fit the model to the structure of the data derived from our experiments and observations. The second element captures the actual mechanisms linking land use (particularly fertilization, mowing and grazing), resource competition, and species diversity. 2) In order to better understand the patterns of diversity observed in our experiments and in the field, we will establish a new experiment for measuring growth of individuals without competition to experimental treatments mimicking fertilization, mowing, and trampling under shallow vs. deep soil conditions. The results will also be used to assign realistic values to relevant parameters in our models. 3) We will establish a new, multi-scale observational study in for linking land management, spatial habitat heterogeneity, and the diversity of natural communities. The basic sampling unit of this observational part will match the core experimental unit of the main experiment, and the sampling design will cover a wide range of scales (from few centimetres to hundreds of kilometres). Moreover, by making use of novel collaborations within the Exploratories, especially with CP3, we will incorporate a remote sensing component in our observations to obtain data on small-scale habitat heterogeneity and beta-diversity across all grassland EPs. This multi-scale integration of theoretical, experimental, observational, and remote sensing components will contribute significantly to our understanding of the causal links between land use effects on biodiversity mediated by habitat heterogeneity, and will provide extensive data for future syntheses.