Forecasting an Ecosystem Regime Shift
Although many ecological changes are gradual and reversible, some extensive changes may occur more abruptly when critical thresholds are crossed. Familiar examples are desertification, shifts from grassland to woody vegetation, or collapse of living resources such as fish populations. These unusually large changes, termed "regime shifts", may be irreversible or reversed only at great cost. Scientists are not yet able to predict when a regime shift is likely to occur in a given ecosystem; however, theory from diverse disciplines suggests that regime shifts are preceded by observable increases in variability of system components. The ability to make such predictions could allow managers to intervene before the change occurred.
In a previous whole-ecosystem experiment, our group experimentally induced a regime shift in a lake by adding a top predator (largemouth bass) to shift the system from a planktivorous fish-dominated state to a piscivorous fish-dominated state. Phytoplankton, zooplankton, and small fishes all exhibit early warnings of an impending regime shift. This was the first, large-scale, field experiment testing the hypothesis that a regime shift could be detected prior to its occurrence in an ecosystem.
Our new project will build upon this previous experiment. Nutrients will be added to a lake to experimentally induce an algal bloom. Ecosystem variables (e.g. chlorophyll, phycocyanin, dissolved oxygen) will be monitored at a high frequency for early warnings of shifts to dominance by nuisance levels of cyanobacteria. We will attempt to detect the impending regime shift to cyanobacteria early enough to be able to halt nutrient additions in time to prevent cyanobacterial blooms. Experimental regime shifts will be induced in two lakes, with a third lake serving as an unmanipulated reference system.
Cascade is affiliated with mulitiple Universities .