North Temperate Lakes

Catastrophic ecological regime
shifts may be announced in advance by statistical early warning signals such as
slowing return rates from perturbation and rising variance. The theoretical
background for these indicators is rich, but real-world tests are rare,
especially for whole ecosystems. We tested the hypothesis that these statistics
would be early warning signals for an experimentally induced regime shift in an
aquatic food web. We gradually added top predators to a lake over 3 years to
destabilize its food web. An adjacent lake was monitored simultaneously as a
reference ecosystem. Warning signals of a regime shift were evident in the
manipulated lake during reorganization of the food web more than a year before
the food web transition was complete, corroborating theory for leading
indicators of ecological regime shifts.