Postscriptum

The reader of this volume will hopefully agree with the authors that we have developed an ecosystem theory. The theory has been presented with the concept of exergy as the central issue. However, as pointed out many times in the volume, there are other approaches that are equally valid and which in some context may offer a better understanding than the approach presented here. These other approaches are, however, completely consistent with the theory presented in this volume. The various approaches form a pattern of ecological theories. It is not surprising that complex systems such as the ecosystem require more than one explanation to give a complete description. Even light requires two descriptions to be consistent with the observations; how many descriptions do we need for the ecosystem that is much more complex than light? So, the message is hopefully that various theories form a pattern and that we have a theory which can be applied much more widely than has been the case up to today. The pattern of theories has emerged in system ecology quite recently. The theory is, therefore, not without flaws. On the contrary, during the coming years it is necessary to improve the theory. Some of the formulation will be reformulated and expressed more clearly. Other basic laws may be added. Some detail of the present fundamental laws will perhaps be shown to be wrong and will therefore require more radical changes of the basic laws. It is not surprising, because this is how science develops.

The ecosystem theory presented in the previous 13 chapters can be reformulated in a compressive form as the following eight laws:

IA. Mass, for instance accounted as the elements, is conserved in ecosystems.

IB. Energy is conserved in ecosystems.

2. All processes in ecosystems are irreversible (this is probably the most useful way to express the Second Law of Thermodynamics in ecology). Another useful formulation, where the Second Law is applied to an ecosystem, is: Ecosystems are driven by an input of low entropy energy, which is transmitted, after its usage for maintenance of the ecosystem, to the environment as high entropy energy.

3. At 0 K, neither disorder nor order (structure) can be created. At increasing temperature, the processes creating order (structure) happen faster, but also the cost of maintaining the structure in the form of disordering processes gets higher. Carbon-based life is, therefore, found at the temperatures where there is a good balance between the rates of two opposite processes, i.e. at about 250-350 K.

4. When a system receives a through-flow of exergy, the system will, after covering the maintenance energy, use the exergy to move away from thermodynamic equilibrium. If more possibilities are offered, the one which most moves the system farther away (indicated as growth) from thermodynamic equilibrium will be selected.

Towards a Thermodynamic Theory for Ecological Systems, pp. 351-354 © 2004 Elsevier Ltd. All Rights Reserved.

5. The growth of an ecosystem is possible by increase in the physical structure (biomass), by increase in the network (more cycling) and by increase of information embodied in the system. All three growth forms imply that the system is moving away from thermodynamic equilibrium and are associated with an increase of (1) the exergy stored in the ecosystem, (2) the through-flow (power) and (3) the ascendancy. The ecosystem receiving solar radiation will attempt to get maximum exergy storage, maximum power and maximum ascendancy.

6. The carbon-based life on Earth has a characteristic basic biochemistry, which all organisms share. This implies that many biochemical compounds can be found in all living organisms. They have, therefore, almost the same elementary composition and the composition of all organisms can be represented in a relatively narrow range of about 25 elements in total.

7. Biological systems are organized hierarchically (O'Neill et al., 1986). The variables describing the state at any level are determined by the processes at their immediate lower levels. Thereby, each level gets emerging properties.

These laws can also be used in ecology to explain ecological rules and observations. It is intuitively clear that the time has come to turn ecology into a theoretical science in line with physics. However, the basic ecological theory is young and, only a few years ago, it was acknowledged that the various ecological theories form a consistent pattern that can be used as a theoretical foundation of ecology.

Hopefully, all ecologists will use the opportunity to explain their observations and rules theoretically, but unfortunately the interactions between general ecologists and system ecologists (more theoretically inclined ecologists) are very limited. It is the hope of the authors of this volume that the presented pattern of ecological theory will encourage general ecologists to apply the ecological theories more widely. Let us propose that the big international and national meetings in ecology are used to encourage interactions between the two ecologies for the mutual benefit. A weak point in theoretical ecology can only be revealed by an application of the theory to explain observations made by the general ecologists and the ecological theory can be applied by general ecologists to support ecological observations. All scientific disciplines require not only observations and theory, but also a close cooperation between the two. Rapid and further progress in ecology is only possible through many and frequent interactions between observations and theory.

We would, however, propose to work with seven basic laws of system ecology to explain observations and rules in ecology and to understand reactions of ecosystems. Only by working with the laws can we find the corrections, improvements and additions to these laws that are needed. Only by trying to make ecology a theoretical science will we be able to build a solid theory of ecosystems in ecology.

Note that, at present, in environmental sciences, and particularly in ecology, we have a curious state-of-the-arts. On the one hand, a lot of different empirical information (experiments and observations in vitro and in vivo, etc.) on biological objects is collected, sometimes to such a fantastic degree of detail that it even becomes unclear how to use this information for further investigations. On the other hand, there are large lacunas in our positive knowledge about the mechanisms of ecosystem functioning, the character of interaction between an ecosystem's components, etc. In order to fill these lacunas we have to perform such an amount of work that it is not serious even to speak about it. As a result, these lacunas are filled by different hypotheses that are quite reasonable sometimes, but sometimes amount to no more than just being witty. Hence, it seems to us that the application of thermodynamic concepts gives a maximal guarantee of success on the way towards the construction of a general ecological theory.

Such properties of "information" provision in ecology naturally form two classes of ecological models. For the first class, the process of "natural selection" on the set of models, where the information is reasonably averaged and maximally aggregated in order to construct a suitable "thermostat" (in the thermodynamic sense of the word), is typical. The latter implies the possibility of representation of the modelled object as some unique system and its environment. Note that such a type of representation is a foundation stone of the exergy concept. The final result of selection is "analytical" models (for instance, a "prey-predator" model) that are outwardly simple, but their dynamics are complex. The Modelsauria that form the second class cannot survive here. Nevertheless, these models that try to use all the present information do exist (these are so-called simulation or portrait models). The algorithm of their construction is very simple: this is the Irish ragout recipe described by Jerome K. Jerome in "Three men in a boat": to put everybody into one pot, to mix it up, and then to boil. Of course, in this case we avoid the complex of "to splash out a tot with water"; that is inherent in models of the first class, but then we can never distinguish the simulation of reality from the artefact of modelling.

How can we get over the scarcity of information in ecological modelling? Firstly, we can use the temporal hierarchy that is usual in the ecosystem. Such an approach (well known in thermodynamics) allows distinguishing between "fast" and "slow" variables. In this case, we can always assume that the system reaches its equilibrium quickly, and then it slowly evolves in a quasi-stationary regime. The latter is a typical dynamics of the system in classic thermodynamics. In any case, the application of different time scales allows significant simplification of the original problem.

The second method is the use of different optimal principles for the completeness of models. In those cases where we do not have sufficient information about some "intimate" control mechanisms in the living systems, we exploit the perpetual teleologicity of the human mentality. It seems to us that the teleological formulations are more "scientific". The latter is very important when it is necessary to get over the subconscious suspicion of the representatives of descriptive natural sciences, of mathematical and physical ("simplifying the real complexity of Nature") models. Perhaps the teleological formulation of several biological rules and laws is a manifestation of this subconscious reaction(?). In the end, we are simply very lucky that the descriptive language of thermodynamics is teleological.

So, at the stage of construction of the primary model, we use:

1. Conservation laws, later on, are set as an invariable part of the model structure.

2. Some general information about the system's temporal and spatial hierarchies.

3. Some general information about the structure of matter, energy and information flows.

4. Extreme (optimal) teleological principles.

Note that any thermodynamic theory is constructed in accordance with this scheme (including even the classic thermodynamics).

Finally, concluding our book, we would like to stress once again that a thermodynamic theory for ecological systems may by no means be associated with the solved or nearly solved problems. We are still greatly restricted by the burden of ideas and concepts from classic thermodynamics, and therefore any new ideas, concepts and methods are only to be welcomed. We have introduced a few ideas in this volume, but many more are still needed. Perhaps we can say that such a thermodynamic theory is only in the formative stage, therefore...

(to be continued)

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