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

溪流的生物学和化学会随着温度和降雨模式的变化而变化。 温度和降水量的变化可能会导致溪流的生物学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，我们需要了解导致溪流生物学和化学可预测和突然反应的环境条件。该奖项将支持研究了解生物控制和环境限制的结构和功能的流在南德克萨斯州。这项研究将利用半干旱到中温的降雨梯度，其特点是在85厘米/年降雨量下，溪流群落组成和生态系统功能会发生突然变化。该研究将包括实地观察，操纵实验和建模的混合。本科生（包括少数民族）和研究生的培训以及通过一个既定的K-12计划的推广将有助于该项目？这个项目将促进我们对为什么环境的微妙变化会导致生态群落的重大和突然重组的理解。沿着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哪些地区将在未来环境变化下经历快速的生态系统变化至关重要。溪流生态系统对降水的变化特别敏感，但可以援引多种机制来解释溪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，这些变化向上级联到更高的营养级;相反，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，这些变化然后向下级联到生态系统过程。通过探索这些替代和潜在的同时运作机制的假设，在一组流沿着在南德克萨斯州的降水梯度，研究将利用一个理想的自然实验沿着与主要调查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如何在世界各地的河流生态系统中类似的过程操作的理解，和基本原则将提高我们对这些过程在所有生态系统的理解。该奖项将支持本科生，研究生，博士后学者和早期职业教师的培训，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。本科生将进行独立研究，并在专业会议上展示结果。K-12推广和成人教育将通过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NSF的法定使命，并通过使用基金会的智力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.