Direct experimental evidence for alternative stable states: a review

This paper reviews the alternative stable state literature and evaluates the validity of the inferences that have been drawn in this body of work. The authors focus exclusively on research involving experimental manipulations, because of the problems of confounding variables in observational studies, and emphasize that the existence of alternate stable states cannot be conclusively documented if the study does not encompass at least one complete turnover time (i.e. the lifespan of the longest living resident species). Such conditions are scientifically laudable, but make it nearly impossible for ecosystems that involve long-lived species and/or potentially exhibit alternative stable states at decadal or centennial time scales (e.g. forests) to be identified. Not surprisingly, Schroder et al. declared the tests conducted in 40% of publications purportedly investigating alternative stable states to be invalid. Of the research that was deemed acceptable, there was a strong bias toward laboratory work, as opposed to field study, as well as a bias towards small and short-lived organisms. They found that 83% of valid laboratory studies demonstrated the existence of alternative stable states, while only 33% of valid field studies did so, all of which consisted of relatively small, short-lived organisms. The authors readily admit the unavoidable biases that result from their strict criteria and assert that there is no reason to believe that alternative stable states do not exist in natural ecosystems with long-lived species, despite the methodological challenges of definitive identification. Although it is true that alternative stable states may exist in many ecosystems within which their existence has not been properly demonstrated, this paper points out that such inferences are sometimes drawn without sufficient rationale.
Schröder, A., Persson, L. & De Roos, A.M. (2005) Direct experimental evidence for alternative stable states: a review. Oikos, 110, 3-19.

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