Land-use effects on patterns and processes in decomposer metacommunities in tree holes

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Metacommunities consist of local communities that are linked by dispersal. They have been suggested to be structured by local environmental conditions, species interactions, dispersal limitation or stochastic processes. The metacommunity concept has been used in conservation to describe the consequences of human-induced landscape fragmentation and to assess related risks to local populations. However, natural metacommunities themselves could serve as indicators of regional environmental impacts such as land-use change. Despite the recent scientific interest in the metacommunity concept and its potential importance for natural communities, it has mostly been treated theoretically or in highly artificial lab experiments. The latter have so far failed to provide conclusive evidence of the driving factors of metacommunity structure.We propose to use the platform of the Biodiversity Exploratories to study a natural metacommunity system: aquatic communities in tree holes. Protists and arthropods colonise these water-filled tree holes and decompose accumulating organic material such as dead leaves.In our research, we will focus on effects of land use on the structure and functions of tree-hole metacommunities. The Exploratories are ideally suited for this project since they provide a large number of forest plots with different management types at three sites. Our model system is a perfect plot-based system because of its relatively small natural size. It will allow us to test the effect of management on metacommunities within plots. We propose to carry out three work packages (WPs) in this project. WP1 will map tree holes and survey their aquatic communities in all forest plots of all exploratories with the aim to identify the major drivers of tree-hole characteristics, and of the structure and functioning of their communities in relation with land use. WP2 will use an experiment in selected natural tree holes to mimic changes that might arise with land-use change. Specifically, we will manipulate bottom-up and top-down forces by modifying resource input and excluding large terrestrial predators. We will measure community responses in order to quantify and mechanistically assess the influence of these changes.WP3 will set up artificial tree holes and experimentally examine community assembly processes during tree-hole colonisation in detail, additionally testing the influence of resource quality. In a collaborative project we will furthermore compare tree-hole metacommunities with forest-floor decomposer systems. We will evaluate generalities and differences to reveal the functional mechanisms behind metacommunity assembly.Upon the completion of this project, we will have contributed fundamental ecological knowledge by mechanistically describing the major drivers of tree-hole metacommunity assembly, structure and function. Furthermore, we expect to be in a better position to predict consequences of land-use change for metacommunities.