Iceland is widely known for its beautiful landscape of volcanoes and glaciers, but few understand the curious arthropod food web surrounding Lake Myvatn. Claudio Gratton, someone who understands this system well, is a Professor of Entomology at the University of Wisconsin, Madison. He is currently studying the aquatic-terrestrial linkages in the landscape, specifically the role midges play in the nitrogen cycle. Lake Myvatn, located in northern Iceland just below the Arctic Circle, is known as “Midge Lake” due to the massive numbers of these insects that emerge from this lake in some years. Midge (Tanytarsus gracilentus and Chironomus islandicus, family: Chironomidae) emergences fluctuate year to year, with major emergences seen every 5 to 8 years (Einarsson et al. 2002; Ives et al. 2008). In high midge emergence years, they can contribute approximately 55
These midges have important impacts on the surrounding environment by providing food for predators, distracting predators from other possible prey, and altering plant composition. The main predators of these midges are web-building spiders. On years when midge density is extraordinarily high, these will aggregate in larger numbers near the lake. Increased midge numbers reduce the predation of leafhoppers by web-building spiders. When spider density was increased, midges still reduced spider predation on other prey species by distracting the predators (Dreyer et al. 2016).
Increased midge biomass has also been shown to increase the density of graminoid plant species (herbaceous, grass-like) and decrease the number of health plant
shifts, with graminoids dominating in the press treatment plots (Gratton et al. in review). Midge populations at Lake Myvatn are known to influence the surrounding landscape and fluctuate year to year, therefore it is likely that similar press and pulse effects are impacting the plant communities surrounding Lake Myvatn.
While it seems that the Lake Myvatn study system is unique, there are many other instances where insects impact the landscape. Some examples include: periodic cicadas, locust swarms, monarch migration, and mayfly emergences. These insect phenomena can have long- and short-term impacts on the environment and can link ecosystems.
About the Authors:
Olivia Bernauer is a Master’s student in Dennis vanEngelsdorp’s bee lab working to better understand the floral preferences of Maryland’s wild, native pollinators.
Meghan McConnell is a Master’s student in Dennis vanEngelsdorp’s Lab studying honey bees with a focus on non-chemical control of varroa mites. After 5 years at UMD with the bee lab and Bee Informed Partnership, she will be the Delaware State Apiarist.
Dreyer, J., Townsend, P. A., III, J. C. H., Hoekman, D., Vander Zanden, M. J. and Gratton, C. (2015), Quantifying aquatic insect deposition from lake to land. Ecology, 96: 499–509. doi:10.1890/14-0704.1
Dreyer, J., Hoekman, D. and Gratton, C. (2016), Positive indirect effect of aquatic insects on terrestrial prey is not offset by increased predator density. Ecol Entomol, 41: 61–71. doi:10.1111/een.12272
Einarsson, Á., Gardarsson, A., Gíslason, G. M. and Ives, A. R. (2002), Consumer–resource interactions and cyclic population dynamics of Tanytarsus gracilentus (Diptera: Chironomidae). Journal of Animal Ecology, 71: 832–845. doi:10.1046/j.1365-2656.2002.00648.x
Ives, Anthony R., Árni Einarsson, Vincent A. A. Jansen, and Arnthor Gardarsson. 2008. “High-Amplitude Fluctuations and Alternative Dynamical States of Midges in Lake Myvatn.” Nature 452 (7183): 84–87. doi:10.1038/nature06610.