Systems Ecology Ten Tentative Fundamental Laws An Attempt to Formulate an Ecosystem Theory

A tentative ecosystem theory consisting of eight basic laws has previously been presented, but it seems to be an advantage to split one of the laws into three due to some recent results, which are presented below with a few comments.

1. All ecosystems are open systems embedded in an environment from which they receive energy (matter) input and discharge energy (matter) output. From a thermodynamic viewpoint, this principle is a prerequisite for ecological processes. If ecosystems could be isolated, then they would be at ther-modynamic equilibrium without life and without gradients. This law is rooted in Prigogine's use of thermodynamics far-from-thermodynamic equilibrium. The openness explains, according to Prigogine, why the system can be maintained far-from-thermodynamic equilibrium without violating the second law of thermodynamics.

2. Ecosystems have many levels of organization and operate hierarchically. This principle is used again and again when ecosystems are described: atoms, molecules, cells, organs, organisms, populations, communities, ecosystems, and the ecosphere. The law is based on the differences in scale of local interactions. The distance between components becomes essential because it takes time for events and signals to propagate. Ecological complexity makes it necessary to distinguish between different levels with different local interactions.

3. Thermodynamically, carbon-based life has a viability domain determined between about 250 and 350 K. It is within this temperature range that there is a good balance between the opposing ordering and disordering processes: decomposition of organic matter and building of biochemically important compounds. At lower temperatures the process rates are too slow and at higher temperatures the enzymes catalyzing the biochemical formation processes decompose too rapidly. At 0 K there is no disorder, but no order (structure) can be created. At increasing temperatures, the order (struc-ture)-creating processes increase, but the cost of maintaining the structure in the face of disordering processes also increases.

4. Mass, including biomass, and energy are conserved. This principle is used again and again in ecology and particularly in ecological modeling.

5. The carbon-based life on Earth has a characteristic basic biochemistry which all organisms share. It implies that many similar biochemical compounds can be found in all living organisms. They have largely the same elementary composition, which can be represented using around 25 elements. This principle allows one to identify stoichio-metric relations in ecology.

6. No ecological entity exists in isolation but is connected to others. The theoretical minimum unit for any ecosystem is two populations, one that fixes energy and another that decomposes and cycles waste, but in reality viable ecosystems are complex networks of interacting populations. This reinforces the openness principle at the scale of the individual component. The network interactions provide the environmental niche in which each component acts. This network has a synergistic effect on the components: the ecosystem is more than the sum of the parts.

7. All ecosystem processes are irreversible (this is probably the most useful way to express the second law ofthermodynamics in ecology). Living organisms need energy to maintain, grow, and develop. This energy is lost as heat to the environment, and cannot be recovered again as usable energy for the organism. Evolution can only be understood in the light of the irreversibility principle rooted in the second law of thermodynamics. Evolution is a step-wise development based on previously achieved solutions to survive in a changing and dynamic world. Due to the structural and genetic encapsulation of these solutions, evolution has produced more and more complex solutions. Eco-exergy expressed by Kullbach's measure of information (see Exergy) is one way to measure this development.

8. Biological processes use captured energy (input) to move further from thermodynamic equilibrium and maintain a state of low-entropy and high-exergy relative to its surrounding and to thermodynamic equilibrium. This is just another way of expressing that ecosystems can grow. It has been shown that eco-exergy of an ecosystem corresponds to the amount of energy that is needed to break down the system.

9. After the initial capture of energy across a boundary, ecosystem growth and development is possible by (1) an increase of the physical structure (biomass), (2) an increase of the network (more cycling), or (3) an increase of information embodied in the system. All three growth and development forms imply that the system is moving away from thermodynamic equilibrium and all three are associated with an increase of (1) the eco-exergy stored in the ecosystem, (2) the energy flow in the system (power), and (3) the ascendency. When cycling increases, the eco-exergy storage capacity, the energy-use efficiency, and space-time differentiation all increase. When the information increases, the feedback control becomes more effective, the animal gets bigger, which implies that the specific respiration decreases, and there is a tendency to replace r-strategist with i-strategists. Notice that the first growth form corresponds to the eco-exergy of organic matter, 18.7 kJg-1, while the increase of the network plus the increase of the information correspond to the eco-exergy calculated as (/3-1)c (see Exergy). Notice also that the three growth and development forms are in accordance with EP Odum's trends of ecosystem development (Table 1). A typical growth and development sequence is present as follows (Figure 1): increased biomass (form 1) has a positive feedback allowing even more additional solar energy capture, until a limit of around 75% of the available solar energy is reached. Thereafter the ecosystem continues to grow and develop by increasing network interactions (form 2) and improving energy efficiencies (form 3).

10. An ecosystem receiving solar radiation will attempt to maximize eco-exergy storage or maximize power such that if more than one possibility is offered, then in the long-run the one which moves the system furthest from thermodynamic equilibrium will be selected. The eco-exergy storage and energy flow increase during all three growth and development forms -see above. When an ecosystem evolves it can apply all three forms in a continuous Darwinian selection process. The nested space-time differentiation in organisms optimizes thermodynamic efficiency as expressed in the tenth law, because it allows the organism to simultaneously exploit equilibrium and nonequilibrium energy transfer with minimum dissipation.

Table 1 Differences between initial stage and mature stage according to Odum (1959 and 1969) are indicated with reference to the three growth forms

Growth form

Properties

Early stages

Late or mature stage

1 (biomass)

Production /respiration

>>1 <<1

Close to 1

Production/biomass

High

Low

Respiration/biomass

High

Low

Yield (relative)

High

Low

Total biomass

Small

Large

Inorganic nutrients

Extra biotic

Intra biotic

2 (network)

Patterns

Poorly organized

Well organized

Niche specialization

Broad

Narrow

Life cycles

Simple

Complex

Mineral cycles

Open

Closed

Nutrient exchange rate

Rapid

Slow

Life span

Short

Long

Ecological network

Simple

Complex

Stability

Poor

Good

Ecological buffer capacity

Low

High

3 (information)

Size of organisms

Small

Large

Diversity, ecological

Low

High

Diversity, biological

Low

High

Internal symbiosis

Undeveloped

Developed

Stability (resistance to external perturbations)

Poor

Good

Ecological buffer capacity

Low

High

Feedback control

Poor

Good

Growth form

Rapid growth

Feedback controlled growth

Types

/--strategists

K-strategists

Reproduced by permission of Elsevier.

Reproduced by permission of Elsevier.

Ecosystem Stability Resistance

Figure 1 The development of an ecosystem is illustrated by plotting exergy captured from the inflowing solar radiation toward the exergy stored in the ecosystem. Growth form 1 is dominant in the first phase of the development from an early-stage ecosystem to a mature ecosystem. By increasing the biomass the percentage of solar radiation captured increases up to about 80% corresponding to what is physically possible. Growth forms 2 and 3 are dominant in the intermediate phase and when the ecosystem is in a mature stage. Thereby more exergy is stored without increasing the exergy needed for maintenance. The system becomes in other words more effective in the use of the solar radiation according to Prigogine's minimum-entropy principle. The exergy stored is increased for all three growth forms. Reproduced by permission of Elsevier.

Figure 1 The development of an ecosystem is illustrated by plotting exergy captured from the inflowing solar radiation toward the exergy stored in the ecosystem. Growth form 1 is dominant in the first phase of the development from an early-stage ecosystem to a mature ecosystem. By increasing the biomass the percentage of solar radiation captured increases up to about 80% corresponding to what is physically possible. Growth forms 2 and 3 are dominant in the intermediate phase and when the ecosystem is in a mature stage. Thereby more exergy is stored without increasing the exergy needed for maintenance. The system becomes in other words more effective in the use of the solar radiation according to Prigogine's minimum-entropy principle. The exergy stored is increased for all three growth forms. Reproduced by permission of Elsevier.

A special issue of Ecological Modelling (vol. 158) was devoted to use the proposed ecosystem theory to explain ecological observations that were unexplained in the ecological literature.

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