LTREB: Interactions Between Population and Ecosystem Dynamics, and the High-Amplitude Fluctuations of Midge Abundances in Lake Myvatn, Iceland

生态系统是复杂的，因为它们依赖于大量的植物、动物和微生物，这些植物、动物和微生物相互依赖，也依赖于它们所处的环境。这项研究的重点是一个生态系统，Myvatn湖，就存在于那里的物种而言，它很简单，而且自然不稳定。在湖中数量适中的食草动物中，有一种影响很大，它是一种蠓——一种蚊子大小的不咬人的昆虫——在其幼年阶段在湖底觅食。在某些年份，所有从湖中涌出的成年蠓的总重量相当于100头座头鲸的重量，而在其他年份，总重量相当于几只金毛猎犬的重量。这些蠓丰度的波动是不可预测的，每4到10年就会发生一次自然崩溃。这些撞击不是由天气或湖外的任何因素引起的，似乎是湖泊本身自然不稳定的一部分。湖泊生态系统的许多组成部分随着蠓的波动而变化，从依赖蠓作为食物的鸟类的繁殖成功到对湖泊生态系统起重要化学作用的微生物的活动。这些过程发生在所有的生态系统中，但表现出这种不稳定性的生态系统极为罕见。通过了解是什么使Myvatn生态系统自然不稳定，我们可以了解是什么使其他生态系统如此稳定，从而使我们能够预测和管理其他不那么极端的生态系统。该项目将培养研究生和本科生实习生。这项研究包括从Myvatn生态系统中长期收集生物和生物地球化学数据，以及有针对性的实验来测试特定的假设。数据收集建立并扩展了现有的长期数据库，监测了从20世纪70年代开始的一些变量（成年蠓）和80年代开始的一些变量（浮游动物，刺鱼）。该项目增加了对许多其他变量的每周监测，包括蠓幼虫密度、底栖生物初级产量以及中上层和底栖生物营养物质。有目标的实验涵盖了广泛的研究问题，包括(i)蠓作为生态系统工程师的作用，改变底栖生物条件以增加初级生产并可能改变营养循环，（ii）由蠓丰度和中上层蓝藻繁殖的时空波动引起的底栖生态系统过程的波动，以及（iii）底栖生物和藻类物种组成的变化既是蠓种群波动的后果也是其原因。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。

Ecosystems are complicated because they depend on large numbers of plants, animals, and microbes that depend on each other as well as the environment in which they live. This research focuses on an ecosystem, Lake Myvatn, that is simple in terms of the species that exist there, and is naturally unstable. Of the moderate number of herbivores in the lake, one has an outsized effect, a species of midge -- a non-biting, mosquito-sized insect -- that in its juvenile stage feeds at the bottom of the lake. In some years, the total weight of all adult midges swarming out of the lake is equivalent to the weight of 100 humpback whales, while in other years the total weight is equivalent to a few golden retrievers. These fluctuations in midge abundances are unpredictable, with natural crashes occurring every 4 to 10 years. The crashes are not caused by weather or anything outside the lake, and appear to be part of a natural instability of the lake itself. Many components of the lake ecosystem changes with midge fluctuations, from the breeding success of birds that depend on the midges as food to the activity of microbes that perform essential chemistry for the lake ecosystem. These processes occur in all ecosystems, but ecosystems that show this type of instability are extremely rare. By understanding what makes the Myvatn ecosystem naturally unstable, we can learn what makes other ecosystems as stable as they are, thereby giving us insight into predicting and managing other less-extreme ecosystems. The project will train graduate students and undergraduate interns. The research involves both long-term collection of biological and biogeochemical data from the Myvatn ecosystem and targeted experiments to test specific hypotheses. The data collection builds and expands on an existing long term database, with monitoring of some variables starting in the 1970s (adult midges) and 1980s (zooplankton, stickleback fish). The project has added weekly monitoring of many additional variables, including midge larval density, benthic primary production, and pelagic and benthic nutrients. The targeted experiments cover a wide range of research questions including (i) the role that midges play as ecosystem engineers, changing benthic conditions to increase primary production and possibly change nutrient cycling, (ii) the fluctuations in benthic ecosystem processes caused by spatiotemporal fluctuations in midge abundances and pelagic cyanobacteria blooms, and (iii) changes in benthic and algal species composition as both consequences and causes of midge population fluctuations.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.