Ecosystems have a very complex dynamics. It is rooted in the enormous number of different life forms, that is the result of the evolution and the enormous variability in the life conditions. Ecosystem development can be described by a wide spectrum of ecological indicators and orientors from single species and concentrations of specific chemical pollutants to holistic indicators such as biodiversity and thermodynamic functions. Physical-chemical systems can usually be described by matter and energy relations, while biological systems require a description that encompasses matter, energy, and information. Information has four properties that significantly different from the properties of matter and energy:
(1) Information can, unlike matter and energy, disappear without trace.
(2) Information expressed for instance as eco-exergy is not conserved.
(3) The disappearance and the copying of information that are characteristic processes for living systems, are irreversible processes.
(4) Exchange of information is communication and it is this that brings about the self-organization of life.
The complex dynamic of ecosystems can be determined by the following hypothesis:
If a system receives an input of exergy (energy that can do work), it will perform work. The work performed is first applied to maintain the system far away from thermodynamic equilibrium whereby work capacity is lost by transformation into heat at the temperature of the environment. If more exergy is available, then the system is moved further away from thermodynamic equilibrium, reflected in growth of gradients. If there is offered more than one pathway to depart from equilibrium, then the one yielding the most stored exergy, power, and ascendency will tend to be selected. Or expressed differently: among the many ways for ecosystems to move away from thermodynamic equilibrium, the one optimizing dEx/dt, d(power)/dt, d(ascendency)/dt, and d(gradients)/dt under the prevailing conditions will have a propensity to be selected. The eco-exergy stored, the ascendency, the power, and the gradients are just to be considered four different views (biomass—information accumulation, the ecological network, the flows, and the differences of intensive variables) of the same reaction of ecosystems by moving away from thermodynamic equilibrium. This chapter, several references, and Chapter 9 present several ecological observations and rules that support this hypothesis.
Light requires description as particles (photons) and waves. It is, therefore, not surprising that ecosystem dynamics can be described in several different ways. Due to the high complexity of ecosystems, it is however, not possible to apply these different descriptors of ecosystem dynamics for the entire ecosystems with all its detailed information, but only for models of ecosystems. Dependent on the knowledge about the ecosystem, it can be advantageous to apply eco-exergy (when the concentrations or biomasses of the focal species are known), ascendency (when a good model of the ecological network is known) or power (when the flows are known). Eco-exergy can be found as the sum of the multiple of concentrations and weighting factors considering the information that the various organisms are carrying. Eco-exergy indicates the distance from thermodynamic equilibrium according to the definition; see also Chapter 2, while emergy indicates the cost in the ultimate energy source on earth, solar radiation. The ratio between the two thermodynamic concepts indicates the efficiency of the system—more efficiency if more exergy is obtained relatively to the solar radiation. In Chapter 9 it is shown how this ratio can be applied as a powerful indicator for an ecosystem.
Ecosystems have three growth forms or methods to move away from thermodynamic equilibrium: biomass growth, network growth, or information growth. When an ecosystem has attained a certain level of energy capture, it will be able to continue to generate organismal and structural information such that eco-exergy, throughflow, and ascendency increase throughout development without n-ecessarily an increase in the physical biomass. The above-mentioned three descriptors, eco-exergy, power, and ascendancy will all increase with the three growth forms, while exergy destruction or entropy production only increases with the first growth form and specific entropy only decreases with the second and third growth form.
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