Ecological science has long wrestled with identifying and quantifying the conditions that lead to the sustainability of ecosystem functions and services. In this endeavor, the scientific community has derived a variety of definitions of sustainability to accommodate the variety of dynamics displayed by ecological systems and the various ways that ecological systems are exploited for human health and well-being.
Persistence is probably best understood in ecological science. Over the course of its long history, ecosystem science has routinely focused on quantifying the stocks and flows of materials and energy through the different trophic levels and the attendant feedbacks that maintain system function. This concept is the most easy to translate to other kinds of consumption-production systems because there are direct parallels in the structure of the systems, the kinds of materials and energy that support production, and the thermodynamic laws that the systems must obey. The limitation of persistence as a measure of sustainability is that it assumes unchanging environmental conditions and that all agents within a trophic level interact with their producers in identical ways. Ecological science has shown that these assumptions do not accord with biological reality. Thus, there is a need to devise measures of sustainability for systems in changing environments and for which there are a diversity of consumer and producer agents. The two most commonly used concepts that address change and variability are reliability and resilience. Although these concepts have been well developed, there remains much uncertainty about their broad applicability even to ecological systems.
Ecological science has only recently begun to understand empirically the nature of diversity-stability relationships and some of the conditions that favor these relationships. It is, however, too soon to make sweeping generalizations about the relationships. Nevertheless, there is wide recognition that different species contribute to overall system functioning in many unique but complementary ways, making the case that indicators of sustainability ought to consider the diversity of functional roles of all agents within a trophic level, not just the functional role of the trophic level in the aggregate. For industrial systems, this may require more fine-tuned analyses of the agents that comprise industrial networks, their individual interaction strengths with producers and other consumers, and the emergent collective behavior of the agents before reliable measures of sustainability can be derived.
The concept of alternative states and resilience is even less empirically tractable in several respects. First, there is limited (if any) concrete empirical demonstration that adaptive capacity of agents in a system does indeed lead to system resilience. Evolutionary biology teaches us that it ought to, at least for small to moderate shocks to systems. Thus, it makes some sense to begin analyzing what constitutes adaptive flexibility of industrial agents and whether this enables responses that can indeed buffer sudden shocks. Even so, there are, as yet, no clear a priori measurement criteria for identifying alternative states or defining desirable and undesirable states from a functional standpoint. That said, the concept does raise the prospect that classic measures of sustainability, like persistence, may simply lead to "fiddling while Rome burns" if we use the index to measure sustainability of an undesirable state. The sobering point here is that technological advancement without consideration of the complexity of the whole system may not be the salvation for humankind if its development locks us into states that lead to greater destruction than good.
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