Does the magnitude of wildlife subsidies influence production, stability, and trophic cascades in a large African river?

该项目将研究马拉河的食物网结构和动态。马拉河是一条跨界河流，为塞伦盖蒂-马拉生态系统、近100万农村贫困人口以及5%流入维多利亚湖和尼罗河流域的河流提供水源。马拉河是野生动物唯一的永久水源，因此被认为是塞伦盖蒂的“生命之血”。这一建议的重点是营养物质添加到河流生态系统的影响，从自然和极大的投入河马和角马的营养物质。关键问题是，大量且时间不规律的养分输入如何影响河流生态系统的功能？本项目将在马拉河系统进行一系列实验来解决这个问题。该项目的结果将对河马的分布和丰度以及角马溺水事件的位置和程度进行估计，这将为塞伦盖蒂-马拉生态系统中河马和角马的管理提供重要信息。河马和角马对肯尼亚和坦桑尼亚的旅游经济极为重要，是值得关注的物种。与肯尼亚国家博物馆的合作将提供关于马拉河中昆虫和鱼类的多样性和生物量的重要数据。该项目将培养一名博士后、一名研究生和多名本科生，并通过让未被充分代表的少数民族本科生参与暑期研究，扩大未被充分代表的群体对科学的参与。该项目还将在肯尼亚为美国学生提供实地短期课程。最后，这项研究的结果将通过基于网络的推广活动与全球受众分享，这些活动使用实时出院数据、现场实时照片流以及Twitter和博客更新。能量、物质和生物跨越生态系统边界的运动是许多景观的共同特征。这些空间补贴对社区和生态系统具有强大但多变的影响。空间补贴的大小可能是群落和生态系统水平效应变异性的最重要驱动因素之一。理论表明，低水平的投入可以稳定食物网并增加社区持久性，特别是在补充当地生产力模式时，而高水平的投入会降低食物网的稳定性并增加营养级联的强度。很少有实证研究解决了补贴规模的影响，提出了本提案的核心问题：补贴规模如何影响社区和生态系统过程？马拉河维持着现存最大的陆上迁徙，大约有120万头角马和4000多只河马。河马在日常觅食迁徙中通过排泄和排泄，角马在大规模溺水期间通过尸体输入，在马拉河中形成了从上游到下游不断增加补贴投入的自然梯度。本项目利用全流域比较、原位比较实验和小规模人工河流实验来测试空间补贴的大小如何影响初级和次级生产、营养级联的强度和食物网的稳定性。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。

This project will address food web structure and dynamics in the Mara River, a trans-boundary river that provides water for the Serengeti-Mara Ecosystem, nearly one million rural poor, and 5% of the river flow into Lake Victoria and the Nile Basin. The Mara River is the only permanent source of water for wildlife and is therefore considered the 'life blood' of the Serengeti. This proposal focuses on the effects of nutrient addition to the river ecosystem from natural and exceedingly large inputs of nutrients from hippopotamus and wildebeest. The key question is how do large and irregularly timed nutrient inputs affect the way river ecosystems function? This project will conduct a series of experiments in the Mara river system to address this question. Results of this project will produce estimates of the distribution and abundance of hippos, and the location and magnitude of wildebeest drowning events that will provide important information for the management of hippos and wildebeest in the Serengeti-Mara Ecosystem. Hippos and wildebeest are extremely important to the tourism economy of Kenya and Tanzania and are species of considerable conservation concern. A collaboration with the National Museums of Kenya will provide important data on the diversity and biomass of insects and fish in the Mara River. This project will train a postdoctoral associate, a graduate student, and multiple undergraduate students, and broaden participation of under-represented groups in science by involving underrepresented minority undergraduate students in summer research. This project will also provide field-based short courses in Kenya for US students. Finally, results from this research will be shared with global audiences through web-based outreach initiatives using real-time discharge data, live photo streams from the field, and Twitter and blog updates.The movement of energy, materials, and organisms across ecosystem boundaries is a common feature of many landscapes. These spatial subsidies have strong but variable effects on communities and ecosystems. The magnitude of spatial subsidies may be one of the most important drivers of the variability in community and ecosystem level effects. Theory suggests that low levels of inputs stabilize food webs and increase community persistence, particularly when complementing patterns of local productivity, and high levels of inputs decrease food web stability and increase the strength of trophic cascades. Very little empirical research has addressed the impacts of the magnitude of subsidies, raising the central question of this proposal: how does the magnitude of subsidies influence community and ecosystem processes? The Mara River sustains the largest remaining overland migration of around 1.2 million wildebeest and a population of over 4,000 hippopotamus (hippos). Hippos, through excretion and egestion during daily feeding migrations, and wildebeest, through carcass inputs during mass drownings, create a natural gradient of increasing subsidy inputs from upstream to downstream in the Mara River. This project utilizes basin-wide comparisons, in situ comparative experiments, and small-scale artificial stream experiments to test how the magnitude of spatial subsidies influences primary and secondary production, the strength of trophic cascades, and food web stability.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.