A lake ecosystem is made up of living and nonliving parts that all interact with each other to form a stable system. These interactions assure the lake ecosystem's health and sustainability. It is a fine balance of production and decomposition, made possible by the biodiversity that occurs in a healthy lake ecosystem. Researchers eavesdropping on complex signals from a remote Wisconsin lake have detected what they say is an unmistakable warning--a death knell--of the impending collapse of the lake's aquatic ecosystem. The finding, reported in the journal Science by a team of researchers led by Stephen Carpenter, an ecologist at the University of Wisconsin-Madison (UW-Madison), is the first experimental evidence that radical change in an ecosystem can be detected in advance, possibly in time to prevent ecological catastrophe.
A lake ecosystem is made up of living and nonliving parts that all interact with each other to form a stable system. These interactions assure the lake ecosystem's health and sustainability. It is a fine balance of production and decomposition, made possible by the biodiversity that occurs in a healthy lake ecosystem. Researchers eavesdropping on complex signals from a remote Wisconsin lake have detected what they say is an unmistakable warning--a death knell--of the impending collapse of the lake's aquatic ecosystem. The finding, reported in the journal Science by a team of researchers led by Stephen Carpenter, an ecologist at the University of Wisconsin-Madison (UW-Madison), is the first experimental evidence that radical change in an ecosystem can be detected in advance, possibly in time to prevent ecological catastrophe.
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The findings suggest that, with the right kind of monitoring, it may be possible to track the vital signs of any ecosystem and intervene in time to prevent what is often irreversible damage to the environment.
"With more work, this could revolutionize ecosystem management," Carpenter (one of the authors) says. "The concept has now been validated in a field experiment and the fact that it worked in this lake opens the door to testing it in rangelands, forests and marine ecosystems."
Ecosystems often change in radical ways. Lakes, forests, rangelands, coral reefs and many other ecosystems are often transformed by overfishing, insect pests, chemical changes in the environment, overgrazing and shifting climate. 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. The collapse of the Northern Cod fishery marked a profound change in the ecological, economic and socio-cultural structure of Atlantic Canada. The change was expressed most acutely in Newfoundland, whose continental shelf lay under the region most heavily fished, and whose communities represented the vast majority of those who lost employment as a result of the moratorium.
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.
"The small fish begin to sense there is trouble and they stop going into the open water and instead hang around the shore and structures, things like sunken logs. They become risk-averse." Carpenter says. The biological upshot, says Carpenter, is that the lake became water flea heaven.
Throughout the lake's three-year manipulation, all its chemical, biological and physical vital signs were continuously monitored to track even the smallest changes that would announce what ecologists call a regime shift, where an ecosystem undergoes radical and rapid change from one type to another.
It was in these massive sets of data that Carpenter and his colleagues were able to detect the signals of the ecosystem's impending collapse. Ecologists first discovered similar signals in computer simulations of spruce budworm outbreaks.
Every few decades the insect's populations explode, causing widespread deforestation in boreal forests in Canada. Computer models of a virtual outbreak, however, seemed to undergo odd blips just before the outbreak.
The problem was solved by William "Buz" Brock. Brock utilized a branch of applied mathematics known as bifurcation theory to show that the odd behavior was in fact an early warning of catastrophic change. In short, he devised a way to sense the transformation of an ecosystem by detecting subtle changes in the system's natural patterns of variability.
The catch, however, is that for the early warning system to work, intense and continuous monitoring of an ecosystem's chemistry, physical properties and biota are required.
Such an approach may not be practical for every threatened ecosystem.
For further information: http://nsf.gov/news/news_summ.jsp?cntn_id=119359&org=NSF&from=news
