Exergy and Fisher Information as ecological indices

Ecological indices are used to provide summary information about a particular aspect of ecosystem behavior. Many Such indices have been proposed and here we investigate two: exergy and Fisher Information. Exergy, a thermodynamically based index, is a measure of the maximum amount of useable work that can be extracted when a system is brought into equilibrium with a reference state. The measure for exergy used herein, also includes a factor to weigh the "complexity" of the ecological species. Fisher Information is an old statistical measure that has recently been applied as a way to detect change in system regime and as a measure of system order. These two indices are compared on a 10-compartment food web model undergoing five different perturbation scenarios. This food web model, although simple, allows for some interesting insight into the two indices. The results show that generally, although not always, exergy and Fisher Information respond differently. such that when one increases due to a perturbation the other decreases and vice versa. We provide a discussion as to the usefulness of these metrics as ecological indices and as their potential use as ecological goal functions in light of these findings. (C) 2003 Elsevier B.V. All rights reserved.