Energy intensity, residence time, exergy, and ascendency in dynamic ecosystems

Abstract Several system-wide indicators (energy intensity ∗ net output, exergy, ascendency) have been proposed as optimands in optimizing principles that are useful for predicting how compartment stocks vary over time in perturbed ecosystems. This article investigates how the proposed indicators vary over time in dynamic model ecosystems. The hypothesis is that the indicators will show different sensitivities (i.e., rate of change over time) at times of abrupt changes of availability of energy and rates of cropping/stocking, and that the more sensitive one(s) deserve further study. Application to a four-compartment model ecosystem based on real steady-state data indicates that energy intensity ∗ net output is most sensitive, and ascendency least sensitive. Exergy is or is not sensitive depending on details of the definition; problems of system boundary, disaggregation, and reference levels are still not resolved and are therefore discussed at some length. The dynamic behavior of residence time is also presented.

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