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

元社区由通过扩散联系在一起的当地社区组成。它们被认为是由当地环境条件、物种相互作用、扩散限制或随机过程构成的。元群落的概念已被用于保护，以描述人类造成的景观碎片化的后果，并评估对当地人口的相关风险。然而，自然准群落本身可以作为区域环境影响的指标，例如土地利用的变化。尽管最近人们对元群落的概念及其对自然群落的潜在重要性感兴趣，但它大多是从理论上或在高度人工的实验室实验中进行处理的。到目前为止，后者还没有提供关于元群落结构驱动因素的确凿证据。我们建议利用生物多样性探索的平台来研究一个自然的元群落系统：树洞里的水生群落。原生动物和节肢动物在这些充满水的树洞中定居，并分解积累的有机物质，如枯叶。在我们的研究中，我们将重点研究土地利用对树洞集合群落结构和功能的影响。探索实验室非常适合这个项目，因为它们在三个地点提供了大量不同管理类型的林地。我们的模型系统是一个完美的基于情节的系统，因为它的自然尺寸相对较小。这将使我们能够测试管理对地块内的元社区的影响。我们建议在这个项目中开展三个工作包(WPS)。WP1将绘制树洞地图，并在所有探索区的所有林地调查树洞的水生群落，目的是确定树洞特征的主要驱动因素，以及与土地利用有关的树洞社区的结构和功能。WP2将在选定的天然树洞中进行一项实验，以模拟可能随着土地利用变化而产生的变化。具体地说，我们将通过修改资源投入和排除大型陆地捕食者来操纵自下而上和自上而下的力量。我们将测量社区的反应，以量化和机械地评估这些变化的影响。WP3将建立人工树洞，并在实验中详细检查在树洞殖民期间的社区组装过程，此外还测试资源质量的影响。在一个合作项目中，我们将进一步比较树洞元社区和森林地面分解系统。我们将评估共性和差异，以揭示集合群落背后的作用机制。在这个项目完成后，我们将通过机械地描述树洞集合的主要驱动因素、结构和功能来贡献基础的生态学知识。此外，我们希望能够更好地预测土地利用变化对元社区的影响。

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.