LTREB Renewal: High-amplitude midge fluctuations and the ecosystem dynamics of Lake Myvatn, Iceland

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

Dramatic 'outbreaks' of organisms - locusts, lemmings, insects - draw public attention to the natural world, in part because scientists do not completely understand the causes for these population surges. This study will investigate midges in Lake Mývatn, Iceland, and why their abundance fluctuates over 4 orders of magnitude in irregular cycles lasting 4-7 years. Adult midges that emerge from the lake die on shore. During high-midge years, the weight of midges that are deposited in the surrounding heathland is equivalent to 10 humpback whales, providing food for predators and scavengers, nutrients for plants, and the basis for local agriculture. By synthesizing results from field samples and experiments over several population cycles, this project promises new insights into fundamental scientific questions about the causes and consequences of population outbreaks. The project will engage graduate and undergraduate students who will work at Mývatn each summer, providing them exposure to extreme biology as well as to educational diversity, as they work in both the lake and on the shoreline under the tutelage of an interdisciplinary group of scientists. The public will learn more about midge outbreaks through an ongoing 'Smidge of Midge' blog. Ecosystems that show huge changes through time can reveal the ecological forces that stabilize or destabilize natural dynamics. This project involves both long-term data collection in aquatic and terrestrial systems and targeted experiments to test specific hypotheses. The aquatic data collection will build and expand on an existing database that dates back to the 1970s. The project has added weekly monitoring of many additional variables, including midge larvae density, benthic primary production, and pelagic nutrients. The collection of terrestrial data has continued with the monitoring of midge infall and arthropod communities along transects around the lake that were established in 2008. A suite of targeted experiments will address a wide range of research questions such as (i) the role that midges play as ecosystem engineers, changing benthic conditions to favor large-bodied epibenthic cladocerans over small-bodied infaunal species, (ii) the mutualistic effect that midge larvae have on algal growth, and (iii) the importance of midge adults for the flowering of carnivorous plants. These experimental projects are led by graduate students as part of their PhD theses, and by undergraduate interns as independent projects. This combination of aquatic and terrestrial experiments together with regular sampling will test hypotheses about how the lake and shoreline ecosystems are linked together. The research will examine whether the instability of the lake ecosystem could drive instability of the surrounding ecosystem on land.