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

自1990年以来，我们利用北方森林和邻近草原的下层植被提出了两个主要问题：(i)植物群落是如何结构的；（ii）它们是如何起作用的？这些问题已经通过对自然生态系统的实验操作得到了解决。第一个问题是由两项主要研究解决的。首先，我们将确定植物群落的结构主要是由营养限制、食草性还是它们的相互作用决定的。我们的实验控制土壤养分水平和食草动物水平，然后我们监测对单个植物物种、种群和群落的影响（例如多样性、生物量）。其次，我们正在测试关于物种相互作用在个人和社区层面上的后果的假设。我们的研究旨在确定竞争是否对社区结构产生重大影响，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，我们将确定个人级别的模式是否“扩大”到社区级别的模式，以及“翻译的准确性”是否取决于生产力。第二个问题是关于生物多样性如何决定生态系统的功能，这个问题再次通过两项主要研究得到解决。首先，我们使用了一种叫做“功能基敲除”的去除实验，在这种实验中，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变化，我们可以确定被移除的成分在生态系统功能中的作用（如地上生物量、地上和地下分解率、养分供应率、截光率和土壤含水量）。其次，通过模拟自然系统中的物种损失，结合种子和幼苗的添加，我们可以确定植物物种身份对群落入侵性的影响，以及群落干扰水平对随后入侵的影响。

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.