MINIMUM EXERGY FLOW OF ISOLATED POPULATIONS: THEORY AND EXPERIMENTS
In previous studies [18-22], we proposed an analytical treatment of the evolution of a population numerosity in time based on one single axiom: that resource consumption (of any kind) can be quantified solely in terms of exergy flows. The results show that the dynamics of a relatively complex natural system like a forest, a herd, a species, is amenable to an analytical treatment provided that a small set of relevant parameters is identified which properly describes the main features of the system/environment interactions. The evolution in time of a population for which the above parameters are known can be reproduced with a good degree of accuracy. It is driven by resource availability, and constrained by certain thresholds -expressed in terms of evolutionary competition parameters and individual resource consumption- below or beyond which the system exhibits trends that quantitatively identify its ability to maintain itself (possibly through fluctuations), in a self-preserving, i.e., thermodynamically sustainable, state. Several sets of well-documented experimental results were used to benchmark the method, with very satisfactory results. The application of our method leads to the identification, among different possible solutions (“scenarios”), of the one that promises a less unsustainable future for the population(s) under study. The “sustainability” we are discussing here must be intended in a purely physical sense, since it is derived solely from thermodynamic principles and does not include other sides of the issue (see below, the Discussion section) that may well retain their relevance outside of the conceptual boundaries of the present treatment but are not amenable to a thermodynamic treatment. The study presented in this paper addresses the “reverse” problem: if the population evolution in time is known, what is the necessary amount of primary resources required to reproduce the data? An answer to this question is of the outmost importance for policy makers and energy planners alike, because it allows for the medium- and long range planning of “minimal exergy consumption”. As in our previous papers, a comparison of our results with some of the available experimental evidence is provided.
Exergy, extended exergy accounting, population dynamics, sustainability, thermodynamic sustainability, ecosystems analysis