Principles for Ecological Engineering
Energy signature Self-organization
The set of energy sources or forcing functions which determine ecosystem structure and function
The selection process through which ecosystems emerge in response to environmental conditions by a filtering of genetic inputs (seed dispersal, recruitment, animal migrations, etc.)
The phenomenon, which occurs entirely fortuitously, whereby adaptations that arise through natural selection for one set of environmental conditions just happen also to be adaptive for a new set of environmental conditions that the organism had not been previously exposed to
The energy signature of an ecosystem is the set of energy sources that affects it (Figure 1.6). Another term used for this concept is forcing functions: those outside causal forces that influence system behavior and performance. H. T. Odum (1971) suggested the use of the energy signature as a way of classifying ecosystems based on a physical theory of energy as a source of causation in a general systems sense. A fundamental aspect of the energy signature approach is the recognition that a number of different energy sources affect ecosystems. Kangas (1990) briefly reviewed the history of this idea in ecology. Basically, sunlight was recognized early in the history of ecology as the primary energy source of ecosystems because of its role in photosynthesis at the level of the organism and, by extrapolation, in primary production at the level of the ecosystem. Organic inputs were formally recognized as energy sources for ecosystems in the 1960s with the development of the detritus concept, primarily in stream ecology (Minshall, 1967; Nelson and Scott, 1962) and in estuaries (Darnell, 1961, 1964; E. P. Odum and de la Cruz, 1963). The terms autochthonous (sunlight-driven primary production from within the system) vs. allochthonous (detrital inputs from outside the system) were coined in the 1960s to distinguish between the main energy sources in ecosystems. Finally, in the late 1960s H. T. Odum introduced the concept of auxiliary energies to account for influences on ecosystems from sources other than sunlight and organic matter. E. P. Odum (1971) provided a simple definition of this concept: "Any energy source that reduces the cost of internal self-maintenance of the ecosystem, and thereby increases the amount of other energy that can be converted to production, is called an auxiliary energy flow or an energy subsidy." H. T. Odum (1970) calculated the first energy signature for the rain forest in the Luquillo Mountains of Puerto Rico, which included values for 10 auxiliary energies.
From a thermodynamic perspective, energy has the ability to do work or to cause things to happen. Work caused by the utilization of the energy signature creates organization as the energy is dissipated or, in other words, as it is used by the system that receives it. Different energies (sun, wind, rain, tide, waves, etc.) do different kinds of work, and they interact in systems to create different forms of organization. Thus, each energy signature causes a unique kind of system to develop. The wide variety of ecosystems scattered across the biosphere reflect the many kinds of energy sources that exist. Although this concept is easily imagined in a qualitative sense, H. T. Odum (1996) developed an accounting system to quantify different kinds of energy in the same units so that comparisons can be made and metrics can be used for describing the energetics of systems. Other conceptions of ecology and thermodynamics are given by Weigert (1976) and J0rgensen (2001).
The one-to-one matching of energy signature to ecosystem is important in ecological engineering, where the goal is the design, construction, and operation of useful ecosystems. The ecological engineer must ensure that an appropriate energy signature exists to support the ecosystem that is being created. In most cases the existing energy signature at a site is augmented through design. Many options are available. Subsidies can be added, such as water, fertilizer, aeration, or turbulence, to direct the ecosystem to develop in a certain way (i.e., encourage wetland species by adding a source of water). Also, stressors can be added, such as pesticides, to limit development of the ecosystem (i.e., adding herbicides to control invasive, exotic plant species).
Many kinds of systems exhibit self-organization but living systems are probably the best examples. In fact, self-organization in various forms is so characteristic of living systems that it has been largely taken for granted by biologists (though see Camazine et al., 2001) and is being "rediscovered" and articulated by physical scientists and chemists. Table 1.9 lists some of the major general systems themes emerging on self-organization. These are exciting ideas that are revolutionizing and unifying the understanding of both living and nonliving systems.
Self-organization has been discussed since the 1960s in ecosystem science (Margalef, 1968; H. T. Odum, 1967). It applies to the process by which species composition, relative abundance distributions, and network connections develop over time. This is commonly known as succession within ecology, but those scientists with a general systems perspective recognize it as an example of the larger phenomenon of self-organization. The mechanism of self-organization within ecosystems is a form of natural selection of those species that reach a site through dispersal. The species that successfully colonize and come to make up the ecosystem at a site have survived this selection process by finding a set of resources and favorable environmental conditions that support a population of sufficient size for reproduction. Thus, it is somewhat similar to Darwinian evolution (i.e., descent with modification of species) but at a different scale (see Figure 5.11). In fact, Darwinian evolution occurs within all populations while self-organization occurs between the populations within the ecosystem (Whittaker and Woodwell, 1972). Margalef (1984) has succinctly
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