Midges, the bane of fishermen and stream-side picnics, advance with civilization, Virginia Tech biology graduate student Matthew McTammany has discovered. He will present his research at the American Society of Limnology and Oceanography (ASLO) / Ecological Society of America (ESA) national meeting, which is June 7-12 in St. Louis, Mo.
In research funded in part by the National Science Foundation, McTammany and colleagues investigated the impact of urbanization on the diversity and populations of insects that live some stage of their lives at the bottom of streams. The researchers looked at 12 streams in western North Carolina, counting insects and measuring physical and chemical conditions of the streams. The streams studied come from watersheds that encompass the resort towns of Maggie Valley and Cherokee and the more densely populated Waynesville and Asheville.
Among the insects that have been the most damaged by urbanization are mayflies, stoneflies, and caddisflies, McTammany reports. "They are sensitive to pollution at the larval stages." As fly fishermen know, these insects are popular fish food; when these insects disappear, fish populations are affected.
Left in plentiful supply are midge larvae. "They are pollution tolerant, so you can get thousands per square meter in highly urbanized areas," McTammany says.
While pollution reduces diversity overall it creates advantages for tolerant species. "Their predators may not be tolerant," McTammany says. "Algae, which can be a food source, grows well in urbanized systems in response to runoff from over-fertilized lawns and increased light and temperature from tree removal. Organic matter, also a good food source, can be higher downstream of sewage plants. Finally, tolerant species can have less competition for resources as other species are killed." However, he adds, "some pollution kills everything."