Collaborative Research: TERRG: Thresholds in ecosystem responses to rainfall gradients

溪流的生物和化学成分随着温度和降雨模式的变化而变化。温度和降水的变化可能导致溪流的生物和化学发生可预测的变化，而其他变化则是突然和不可预测的。面对环境变化，我们需要了解环境条件，这些环境条件会对溪流的生物和化学产生可预测和突然的反应。该奖项将支持对南德克萨斯州溪流结构和功能的生物控制和环境限制的研究。该研究将利用半干旱到半干旱的降雨梯度，其特征是在85厘米/年的降雨量下，河流群落组成和生态系统功能会发生突变。这项研究将包括实地观察、操作实验和建模。对本科生（包括少数民族）和研究生的培训以及通过既定的K-12课程的推广将有助于该项目？更广泛的影响。这个项目将促进我们理解为什么环境的细微变化会导致生态群落的重大和突然重组。沿降水梯度的生态系统结构和功能的空间格局表明，阈值效应是普遍和广泛的。因此，了解驱动这些模式的机制对于预测世界上哪些地区在未来环境变化下将经历快速的生态系统转变至关重要。河流生态系统对降水变化特别敏感，但可以援引多种机制来解释在河流中观察到的阈值效应。这些机制包括：1)资源基础的数量、质量、时间稳定性和可预测性的变化，这些变化级联到更高的营养水平；2)影响群落结构的时间稳定性、可预测性和平均环境条件的变化，这些变化随后级联到生态系统过程。通过在南德克萨斯州沿降水梯度的一组溪流中探索这些交替的和可能同时运行的机制假设，该研究将利用一个理想的自然实验以及主要研究人员收集的初步数据的坚实基础。这项研究的结果将反过来告诉我们类似的过程是如何在世界各地的河流生态系统中运作的，基本原理将增强我们对所有生态系统中这些过程的理解。该奖项将支持在西班牙裔服务机构和主要为40%少数民族服务的本科机构培训本科生、研究生、博士后学者和早期职业教师。本科生将进行独立研究，并在专业会议上展示结果。K-12外展和成人教育将通过SIU生态中心和研究生研究助理支持科学（GRASS）计划进行。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The biology and chemistry of streams change in response to changes in temperature and rainfall patterns. Changes in temperature and precipitation may lead to predictable changes in the biology and chemistry of streams, while other changes are abrupt and unpredictable. In the face of environmental change, we need to understand the environmental conditions that result in predictable and abrupt responses to both the biology and chemistry of streams. This award will support research on understanding biological controls and environmental constraints on the structure and function of streams in South Texas. The research will take advantage of a semi-arid to mesic rainfall gradient that features an abrupt shift in stream community composition and ecosystem functioning at 85 cm rainfall/yr. The research will consist of a mix of field observations, manipulative experiments, and modeling. Training of undergraduate (including minority) and graduate students and outreach via an established K-12 program will contribute to the project?s broader impacts.This project will advance our understanding of why subtle shifts in the environment can result in the significant and abrupt reorganization of ecological communities. Spatial patterns in structure and function of ecosystems along precipitation gradients indicate that threshold effects are common and widespread. Therefore, understanding the mechanisms that drive these patterns is essential for forecasting which regions of the world will undergo rapid ecosystem shifts under future environmental change. Stream ecosystems are particularly sensitive to changes in precipitation, but multiple mechanisms can be invoked to explain observed threshold effects in streams. These mechanisms include: 1) Changes in the quantity, quality, temporal stability, and predictability of the resource base, which cascade up to higher trophic levels; and conversely, 2) Changes in the temporal stability, predictability, and average environmental conditions impacting community structure, which then cascade down to ecosystem processes. By exploring these alternate and potentially simultaneously operating mechanistic hypotheses in a set of streams along a precipitation gradient in South Texas, the research will capitalize on an ideal natural experiment along with a strong foundation of preliminary data collected by the principal investigators. The results of this study will in turn inform our understanding of how similar processes operate in stream ecosystems around the world, and the basic principles will enhance our understanding of these processes in all ecosystems. The award will support training of undergraduate, graduate, postdoctoral scholars, and early career faculty at both a Hispanic Serving Institution and a primarily undergraduate institution serving 40% minorities. Undergraduates will conduct independent research and present the results at professional meetings. K-12 outreach and adult education will be conducted through the SIU Center for Ecology and Graduate Research Assistants Supporting Science (GRASS) program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.