On the consistency between thermodynamical and network approaches to ecosystems

If one assumes that biological systems develop in the direction of increasing thermodynamic efficiency, one is led to several conclusions about how interactions between parts of the system, as well as the system as a whole, should evolve. For example, one can show that maximizing efficiency will imply that inputs from the exterior should be maximized, internal transfers should be emphasized above negative exogenous links, the costs of structure maintenance should be minimized, and the heaviest imports should be those most easily accessible. In the network approach to ecosystem development, systems are assumed to change over time so as to increase the information inherent in their patterns of flow connections. This has been expressed quantitatively as a rise in the 'ascendency' of the flow pattern. That these two different views on ecosystem behaviour are essentially consistent is demonstrated by calculating the sensitivities of the ascendency index to individual types of flows. Those changes in flow patterns that augment the ascendency also contribute to increased thermodynamic efficiency. (C) 2000 Elsevier Science B.V. All rights reserved.