Insect carcasses link aquatic and terrestrial ecosystems: lessons from the subarctic  Add To Calendar

Speaker: Claudio Gratton, University of Wisconsin, Madison
Host: Wise and Minor Labs
  • Date(s): Tuesday, 4/19 4:00 PM to Tuesday, 4/19 5:00 PM
  • Campus Address: 4289 SEL, 840 West Taylor

Aquatic insects are ubiquitous and abundant components of terrestrial communities that occur at the water-land interface.  Despite their small size, as aquatic insects move over land and die, they can at times represent a relatively large contribution to ecosystem C and N fluxes, affect food web interactions on land and alter the composition of plant and animal communities.  We have been studying the annual emergences of chironomid (non-biting) midges from the subarctic lake Myvatn in northeastern Iceland to understand the ecosystem and food web effects on near-shore terrestrial ecosystems.   We found that, on average over a three-year period, midge deposition to land near shore reached a peak at about 20 m from shore and contributed as much as 10-15 kg N ha-1 to terrestrial communities.  This amount of N was associated with wholesale changes in plant communities near shore, which had higher N concentrations, and became more dominated by grasses.  Experimental addition of midges found the same general results, with increasing dominance of grasses, incorporation of midge-derived N into plant tissues.  In addition, soil decomposition rates increased when midges were added to soils.  Insect communities also shifted in composition in response to midges, reflecting an increase in decomposers and predatory taxa.  In short, because most aquatic insect production at the water-land boundary goes unconsumed and enters the terrestrial system as carcasses, soil communities and therefore plant communities are altered by their presence to the point where the terrestrial community patterns cannot be fully understood without taking into account their presence.  Although the patterns at Myvatn are extreme, the same processes play out at a smaller scale in most other lakes and streams, making the responses we observe likely widespread in other biomes.