Quantifying sustainability: Resilience, efficiency and the return of information theory

Contemporary science is preoccupied with that which exists; it rarely accounts for what is missing. But often the key to a system's persistence lies with information concerning lacunae. information theory (IT), predicated as it is on the indeterminacies of existence, constitutes a natural tool for quantifying the beneficial reserves that lacunae can afford a system in its response to disturbance, In the format of IT, unutilized reserve capacity is complementary to the effective performance of the system, and too little of either attribute can render a system unsustainable. The fundamental calculus of IT provides a uniform way to quantify both essential attributes - effective performance and reserve capacity - and results in a single metric that gauges system sustainability (robustness) in terms of the tradeoff allotment of each. Furthermore, the same mathematics allows one to identify the domain of robust balance as delimited to a window of vitality that circumscribes sustainable behavior in ecosystems. Sensitivity analysis on this robustness function with respect to each individual component process quantifies the value of that link at the margin, i.e., how much each unit of that process contributes to moving the system towards its most sustainable configuration. The analysis provides heretofore missing theoretical justification for efforts to preserve biodiversity whenever systems have become too streamlined and efficient. Similar considerations should apply as well to economic systems, where fostering diversity among economic processes and currencies appears warranted in the face of over-development. (C) 2008 Elsevier B.V. All rights reserved.