Thermodynamics of an ecosystem interpreted as a hierarchy of embedded systems

A hierarchical understanding of biological systems has prevailed among biologists for more than a century. This ontic perception of the world has deeply influenced the way biological systems have been studied. The resulting methodology has been that the cause(s) for phenomenological behaviour at one level, usually referred to as the focal level, has usually been sought at continuously lower, i.e. at a smaller scale, levels of the biological hierarchy. This is usually presented as a vertical hierarchy of systems consisting of other sub-systems and/or as parts of supersystems. The transfer of this view to ecosystems was made some decades ago and its actuality has been stressed by recent publications on the topic. At the same time, as a consequence of works by Schrödinger and Prigogine, thermodynamical views have been imposed on ecosystems. According to these views biological systems may be understood and studied as self organizing, dissipative structures far from thermodynamical equilibrium. Joining the two views it becomes possible to investigate the flows of an ecosystem in terms of exergy and arrange the system as a hierarchically ordered sequence of systems, thermodynamically embedded in each other. In this paper the use of this principle is illustrated using a simple ecosystem model consisting of an aquatic food chain with recycling via a bacterial/detrital complex. The joining of the two principles seems to deliver an operational framework that opens up for a unification of thermodynamical and network views of ecosystem, to be used with other concepts such as environ analysis, analyses of indirect effects, ascendancy, handling and investigating them on a common basis. The thermodynamical constraints that can be deduced from using this principle may in the future lead to the development of object oriented organized models where thermodynamical relations serve as important constraints to the development of various models of ecosystems.