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

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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.