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

为什么物种在某些组合中被发现，而在其他组合中却没有？为什么有些物种在似乎适合它们需要的栖息地找不到？生态学的一个基本目标是了解物种发生模式的驱动过程。 生物体的“局部”环境可以对其发生的地方产生影响，例如，气候、资源竞争和干扰。 然而，“区域”因素-如生物体在现有生境中定居的能力-也很重要。这个项目解决了两个基本问题：1）在控制物种组成方面，地方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的变化而变化的，以及生物在这些景观中移动的能力？ 该项目将利用河流网络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形式，如蜉蝣和石蛾，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，因为河流具有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。 该项目利用河流恢复活动，其中几乎总是包括大规模的栖息地改造：“当地”因素的最终操纵。 三种类型的方法将被用来解决研究问题：调查恢复网站，实验操纵当地的因素-特别是流底部栖息地功能-在河流系统，和实验使用人工流来控制当地和区域的过程。 该项目将有重要的应用生态学的影响，因为流评估往往涉及表征水生生物群落的假设下，当地的栖息地决定其组成。河流恢复工作（美国估计每年10亿美元）通常是根据这种生物评估技术进行评估的。 以前的研究结果表明，这一假设可能只适用于流网络的特定部分。 这项研究将是第一个开始详细探讨栖息地因素的空间依赖性，不仅推进生态学领域，但提供信息的重要性，河流网络的位置在发展中的期望恢复。

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.