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

生境条件的空间异质性是影响生物多样性的一个主要因素，但在生物多样性探索站中却鲜有研究。我们试图通过整合理论，实验和观测研究，重点是土地管理的异质性和土地利用造成的异质性影响草地多样性的机制，以填补这一空白。我们的项目的一个基本要素是，栖息地异质性可能有积极和消极的影响，物种多样性，由于固有的权衡栖息地异质性的程度和有效面积的数量可供个别物种在社区（AHTO面积异质性权衡）之间的想法。在第一阶段，我们使用分析模型来研究AHTO的一般性质和后果，重点是放松以前这种权衡的公式中的简化假设。同时，我们建立了一个独特的实验装置，用于在高度受控的条件下测试我们的模型产生的预测。在第二阶段，我们将在三个主要方向上开展工作。1)我们将扩展我们的模型向上（通过将我们的本地社区模型扩展到元生态系统框架）和向下（通过明确建模土壤和光资源竞争对个体植物的影响）。升级元素将使模型适合于从我们的实验和观察中获得的数据结构。第二个要素反映了土地利用（特别是施肥、割草和放牧）、资源竞争和物种多样性之间的实际联系机制。2)为了更好地了解在我们的实验和现场观察到的多样性模式，我们将建立一个新的实验，用于测量个体的生长，而不与模拟施肥，割草和踩踏的实验处理竞争。结果也将被用来分配现实的价值观，我们的模型中的相关参数。3)我们将建立一个新的，多尺度的观测研究，以联系土地管理，空间栖息地异质性和自然群落的多样性。这一观测部分的基本取样单位将与主要实验的核心实验单位相匹配，取样设计将涵盖广泛的尺度（从几厘米到几百公里）。此外，通过利用新的合作，特别是与CP3的探索，我们将在我们的观察中纳入遥感组件，以获得小规模的栖息地异质性和β多样性在所有草原EP的数据。这种多尺度的理论，实验，观测和遥感组件的整合将大大有助于我们了解土地利用对生物多样性的影响介导的栖息地异质性之间的因果关系，并将提供广泛的数据为未来的综合。

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.