Indicators of regime shifts in ecological systems: what do we need to know and when do we need to know it?
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CitationContamin, Raphael, and Aaron M. Ellison. 2009. Indicators of regime shifts in ecological systems: what do we need to know and when do we need to know it? Ecological Applications 19(3): 799-816.
AbstractBecause novel ecological conditions can cause severe and long-lasting
environmental damage with large economic costs, ecologists must identify possible
environmental regime shifts and pro-actively guide ecosystem management. As an illustrative
example, we apply six potential indicators of impending regime shifts to Carpenter and Brock’s
(2006) model of lake eutrophication and analyze whether or not they afford adequate advance
warning to enable preventative interventions. Our initial analyses suggest that an indicator based
on the high-frequency signal in the spectral density of the time-series provides the best advance
warning of a regime shift, even when only incomplete information about underlying system
drivers and processes is available. In light of this result, we explore two key factors associated
with using indicators to prevent regime shifts. The first key factor is the amount of inertia in the
system – how fast the system will react to a change in management, given that a manager can
actually control relevant system drivers. If rapid, intensive management is possible, our analyses
suggest that an indicator must provide at least 20 years advance warning to reduce the
probability of a regime shift to < 5%. As time to, or intensity of, intervention is increased, the
necessary amount of advance warning required to avoid a regime shift increases exponentially.
The second key factor concerns the amount and type of variability intrinsic to the system, and the
impact of this variability on the power of an indicator. Indicators are considered powerful if they
detect an impending regime shift with adequate lead time for effective management intervention
but not so far in advance that interventions are too costly or unnecessary. Intrinsic “noise” in the
system obscures the “signal” provided by all indicators and therefore power of the indicators
declines rapidly with increasing within- and between-year variability in measurable variables or
parameters. Our results highlight the key role of human decisions in managing ecosystems and
the importance of pro-active application of the precautionary principle to avoid regime shifts.
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