The biological upshot, says Carpenter, is that the lake became "water flea heaven."
The system becomes one where the phytoplankton, the preferred food of the lake's water fleas, is highly variable.
"The phytoplankton get hammered and at some point the system snap into a new mode," says Carpenter.
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, a UW-Madison economist who for decades has worked on the mathematical connections of economics and ecology.
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 upshot of the Peter Lake field experiment, says Carpenter, is a validated statistical early warning system for ecosystem collapse.
The catch, however, is that for the early warning system to work, intense and continuous monitoring of an ecosystem's chemistry, physical prope
|Contact: Cheryl Dybas|
National Science Foundation