Emergy, environ, exergy and ecological modelling

Hitherto, applied calculations of exergy for higher organisms have been based on traditional thermodynamic considerations, which did not take into account the organizational level of organisms. It seems reasonable to include such perspectives in a thermodynamic evaluation of ecosystems. Therefore, two methods that are theoretically more sound for calculations of exergy for higher organisms are proposed in this paper. The first is based upon the thermodynamic information due to genes. The method is rooted in statistical thermodynamics and should be considered the best candidate for exergy calculations of ecosystems including higher organisms. The second method is a parallel to the method used for calculation of emergy, and is based on the cost of free energy computed from an ecological network. Because this method does not consider the increase of information due to evolution, it should be considered theoretically less sound than the first mentioned method. It is, however, interesting to compare the two methods, as they to a certain extent reflect the differences between emergy and exergy. Emergy attempts, as exergy, to account for the quality of energy by the use of a transformity factor. The transformity factors for calculation of emergy are found from the network as the number of solar equivalents that it has cost to construct the considered organism. Emergy is therefore often more easy to compute, provided that the ecological network is known, while exergy after the new methods for calculations presented here seems to have a better theoretical basis. The two methods tested for calculation of exergy give different results, but the results are in the same order of magnitude. The two major problems in development of ecological models are the parameter estimation and the selection of the best model structure. The latter requires that more ecological system properties are incorporated in our models. A procedure based upon recent developments in ecosystem theory is proposed to meet this requirement. It should be considered a first approach to a theoretical improvement of the modelling procedure for development of models with more ecological properties.