Determinants of community structure: community-level consequences of species interactions and loss of biodiversity

自1990年以来，我们问了两个主要问题，利用下层的北方森林和邻近的草地：（i）植物群落是如何结构化的，（ii）它们是如何运作的？ 这些问题已经得到解决，使用良好的复制实验操作的自然生态系统。 第一个问题由两项主要研究解决。首先，我们将确定植物群落的结构主要是由营养限制，草食动物，或它们的相互作用。我们的实验操纵土壤养分水平和草食动物水平，然后我们监测对单个植物物种，种群和群落（例如多样性，生物量）的影响。 第二，我们正在测试的假设物种相互作用的后果在个人层面和社区层面。我们的研究旨在确定竞争是否对群落结构有重大影响，以及这些影响的大小是否以可预测的方式沿着生产力梯度变化？此外，我们还将确定个人层面的模式是否“扩大”到社区层面的模式，以及“翻译的准确性”是否取决于生产力。 第二个问题是生物多样性如何决定生态系统的功能，并再次通过两项主要研究加以解决。 首先，我们正在使用一种被称为“功能组敲除”的去除实验，在该实验中，植物群落的选定成分被去除。 通过观察群落动态和生态系统功能的相应变化，我们可以确定被移除成分在生态系统功能中的作用（例如地上生物量、地上和地下分解率、养分供应率、光截获和土壤含水量）。其次，通过模拟物种从自然系统中的损失，结合种子和幼苗的添加，我们可以确定植物物种的身份对入侵的社区的影响，以及社区的干扰水平对随后的入侵的影响。

Since 1990 we have asked two primary questions using the understorey of the Boreal Forest and adjacent grasslands: (i) how are plant communities structured, and (ii) how do they function?  These questions have been addressed using well-replicated experimental manipulations of the natural ecosystem.    The first question is addressed by two major studies. First we will determine if the plant community is structured primarily by nutrient limitation, by herbivory, or by their interaction. Our experiments manipulate soil nutrient levels and herbivore levels, and we then monitor the consequences on individual plant species, populations, and communities (e.g. diversity, biomass).  Second, we are testing hypotheses about the consequences of species interactions at an individual-level and community-level. Our studies are designed to determine if competition has significant impacts on community structure and if the magnitude of these impacts change in predictable ways along productivity gradients? In addition we will determine if individual-level patterns "scale up" to community-level patterns, and if the "accuracy of the translation" depends on productivity.    The second question asks how biodiversity determines the functioning of ecosystems, and is again addressed using two major studies.  First, we are using a removal experiment called "a functional group knock-out" in which selected components of a plant community are removed.  By observing the consequent changes in community dynamics and ecosystem function we can determine the role of the removed component in ecosystem function (e.g. above-ground biomass, above and below-ground decomposition rates nutrient supply rates, light interception and soil water content). Second, by simulating species loss from natural systems, in conjunction with seed and seedling additions, we can determine the effect of plant species identity on invasibility of a community, and the effect of the level of the disturbance of the community on subsequent invasion.