Collaborative Research: The role of network topology and environmental filtering in shaping the ecology of spatially structured communities

为什么物种是在某些组合中发现的，而不是在其他组合中？为什么有些物种没有在似乎适合它们需要的栖息地中被发现？生态学的一个基本目标是了解驱动物种发生模式的过程。生物体的“本地”环境可以对其发生的地方施加影响，例如气候、资源竞争和干扰。然而，“区域”因素——比如生物在现有栖息地定居的能力——也很重要。该项目解决了两个基本问题：1)在控制物种组成方面，本地因素与区域因素的相对重要性是什么？2)这种相对重要性是如何随着景观元素以及生物在这些景观中移动的能力而变化的？该项目将利用河网中的水生无脊椎动物群落来解决这两个问题。这些生物包括许多昆虫的幼虫，如蜉蝣和球蝇，以及蜗牛和小龙虾等动物。这些社区是解决这些问题的理想选择，因为河流有着非常独特的分支结构。此外，河流遭受严重的人类退化，水生无脊椎动物经常被用作水质指标。该项目利用了河流恢复活动的优势，这些活动几乎总是包括大规模的栖息地改造：对“当地”因素的最终操纵。将采用三种类型的方法来解决研究问题：恢复地点的调查，对河流系统中当地因素的实验操纵-特别是河底生境特征-以及使用人工溪流来控制当地和区域过程的实验。该项目将对应用生态学产生重要影响，因为河流评估往往涉及水生群落的特征，假设仅由当地生境决定其组成。溪流恢复工作（在美国估计每年花费10亿美元）通常基于这种生物评估技术进行评估。先前的研究结果表明，这种假设可能只适用于流网络的特定部分。该研究将首次开始详细探索生境因子的空间依赖性，不仅推动了生态学领域的发展，而且提供了关于河网位置在制定恢复期望中的重要性的信息。

Why are species found in certain combinations and not others? Why are some species not found in habitats that seem suitable for their needs? A fundamental goal of ecology is to understand the processes that drive patterns in species occurrence. An organism's "local" environment can exert influence on where it occurs, e.g., climate, competition for resources, and disturbance. However, "regional" factors - such as the ability of organisms to colonize available habitat - are also important. This project addresses two fundamental questions: 1) What is the relative importance of local versus regional factors in controlling species composition? 2) How does that relative importance shift with elements of landscapes, and the ability of organisms to move across those landscapes? The project will address these two questions using communities of aquatic invertebrates in river networks. These organisms include the larval forms of many insects, such as mayflies and caddisflies, and animals like snails and crayfish. These communities are ideal for addressing the questions because rivers have a very distinct, branching configuration. Furthermore, rivers endure intense human degradation, and aquatic invertebrates are often used as indicators of water quality. The project takes advantage of stream restoration activity, which almost always includes large-scale habitat modification: the ultimate manipulation of "local" factors. Three types of approaches will be employed to address the research questions: surveys of restoration sites, experimental manipulations of local factors - specifically stream-bottom habitat features - in river systems, and experiments using artificial streams to control for both local and regional processes. The project will have important implications for applied ecology because stream assessment often involves characterizations of aquatic communities under the assumption that local habitat alone determines their composition. Stream restoration efforts (estimated at $1 billion annually in the U.S.) are often evaluated based on such bioassessment techniques. Previous findings suggest that this assumption may apply only to specific portions of a stream network. This research will be the first to begin to explore spatial dependence of habitat factors in detail, not only advancing the field of ecology, but providing information about the importance of river network position in developing expectations for restoration.