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主要因素，但在生物多样性研究领域研究较少。我们试图通过整合理论、实验和观测研究来填补这一空白，重点关注土地管理异质性和土地利用异质性影响草地多样性的机制。我们项目的一个基本要素是，由于生境异质性程度与群落中单个物种可用有效面积之间的内在权衡（AHTO-area-heterogeneity trade-off），生境异质性可能对物种多样性产生积极和消极的影响。在第1阶段，我们使用分析模型来研究AHTO的一般性质和结果，重点是放松对这种权衡的先前公式中所做的简化假设。同时，我们建立了一个独特的实验装置，用于在高度控制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扩展我们的工作。1)我们将向上扩展我们的模型（通过将我们的本地社区模型扩展到一个元社区框架），向下扩展我们的模型（通过明确地模拟单个植物对土壤和光照资源的竞争的影响）。升级元素将使模型适合于我们从实验和观察中得到的数据结构。第二个要素抓住了连接土地利用（特别是施肥、割草和放牧）、资源竞争和物种多样性的实际机制。2)为了更好地理解我们在实验和田间观察到的多样性模式，我们将建立一个新的实验来测量个体的生长，而不与浅土层和深土层条件下模拟施肥、刈割和踩踏的实验处理竞争。结果还将用于为我们的模型中的相关参数分配现实值。3)建立联系土地管理、空间生境异质性和自然群落多样性的新型多尺度观测研究。该观测部分的基本采样单元将与主实验的核心实验单元相匹配，采样设计将涵盖广泛的尺度（从几厘米到数百公里）。此外，通过利用各探索区（特别是与CP3）之间的新型合作，我们将在观测中纳入遥感成分，以获取所有草原ep的小尺度栖息地异质性和β -多样性数据。这种对理论、实验、观测和遥感成分的多尺度整合将有助于我们理解由生境异质性介导的土地利用对生物多样性的影响之间的因果关系，并将为未来的综合研究提供广泛的数据。

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.