For humans, ecosystem change can impact economies and livelihoods such as when forests succumb to an insect pest, rangelands to overgrazing, or fisheries to overexploitation.
A vivid example of a collapsed resource is the Atlantic cod fishery.
Once the most abundant and sought-after fish in the North Atlantic, cod stocks collapsed in the 1990s due to overfishing, causing widespread economic hardship in New England and Canada. Now, the ability to detect when an ecosystem is approaching the tipping point could help prevent such calamities.
In the new study, the Wisconsin researchers, collaborating with scientists at the Cary Institute for Ecosystem Studies in Millbrook, N.Y., the University of Virginia in Charlottesville and St. Norbert College in De Pere, Wis., focused their attention on Peter and Paul Lakes, two isolated and undeveloped lakes in northern Wisconsin.
Peter is a six-acre lake whose biota were manipulated for the study and nearby Paul served as a control.
The group led by Carpenter experimentally manipulated Peter Lake over a three-year period by gradually adding predatory largemouth bass to the lake, which was previously dominated by small fish that consumed water fleas, a type of zooplankton.
The purpose, Carpenter notes, was to destabilize the lake's food web to the point where it would become an ecosystem dominated by large predators.
In the process, the researchers expected to see a relatively rapid cascading change in the lake's biological community, one that would affect all its plants and animals in significant ways.
"We start adding these big ferocious fish and almost immediately this instills fear in the other fish," Carpenter says.
"The small fish begin to sense there is trouble and they stop going into the open water and
|Contact: Cheryl Dybas|
National Science Foundation