Researchers changed the structure of the food web in Peter Lake, in Wisconsin, by adding predatory fish.
Within three years, the fish had taken over, producing a decline in tiny water plants and an explosion in water fleas.
Writing in the journal Science, the researchers say the change was preceded by signals that could be used to predict similar collapses elsewhere.
In particular, rapid swings in the density of plants and fleas indicated the food web was unstable and about to change.
The idea that such early warning signals ought to exist is not new - but the researchers say this is the first time it has been demonstrated experimentally.
"For a long time, ecologists thought these changes couldn't be predicted," said research leader Stephen Carpenter from the University of Wisconsin in Madison, US.
"But we've now shown that they can be foreseen. The early warning is clear; it is a strong signal." (read more)