Ecological engineers design, build, and operate new ecosystems for human purposes. Engineering contributes to all of these phases but, as noted above, the design phase is critical. While the designs in ecological engineering use sets of species that have evolved in natural systems, the ecosystems created are new and have never existed before. Some names have been coined for the new ecosystems including "domestic ecosystems" (H. T. Odum, 1978a), "interface ecosystems" (H. T. Odum, 1983), and "living machines" (Todd, 1991). The new systems of ecological engineering are the product of the creative imagination of the human designers, as is true of any engineering field, but in this case the self-organization properties of living systems also make a contribution. This entails a natural selection of species appropriate for the boundary conditions of the design provided by the designer. Thus, ecologically engineered systems are the product of input from the human designer and from the system being designed, through the feedback of natural selection. This quality of the design makes ecological engineering a unique kind of engineering and an intellectually exciting new kind of applied ecology.
Many practical applications of ecological engineering exist, though often with different names (Table 1.6). The applications are often quite specific, and only time will tell if they will eventually fall under the general heading of ecological engineering. All of the applications in Table 1.6 combine a traditional engineering contribution to a greater or lesser extent, such as land grading, mechanical pump systems, or material support structures, with an ecological system consisting of an interacting set of loosely managed species populations. The best known examples of ecological engineering are those which require an even balance of the design between the engineering and the ecological aspects.
Environmental problem solving is a goal of ecological engineering, but only a subset of the environmental problems that face humanity can be dealt with by constructed ecosystem designs. Most amenable to ecological engineering may be various forms of pollution cleanup or treatment. In these cases, ecosystems are sought that will use the polluted substances as resources. Thus, the normal growth of the ecosystem breaks down or stabilizes the pollutants, sometimes with the generation of useful byproducts. This is a case of turning problems into solutions, which is an overall strategy of ecological engineering. Many examples of useful byproducts from ecologically engineered systems are described in this book.
An ecological engineering design relies on a network of species to perform a given function, such as wastewater treatment or erosion control. The function is usually a consequence of normal growth and behavior of the species. Therefore, finding the best mix of species for the design of a constructed ecosystem is a challenge. The ecological engineer must understand diversity to meet this challenge. Diversity is one of the most important concepts in the discipline of ecology (Huston, 1994; Patrick, 1983; Rosenzweig, 1995). Table 1.7 compares two ecosystems in order to illustrate the relative magnitudes of local species diversity. Globally, there are over a million species known to science, and estimates of undescribed species (mostly tropical rainforest insects) range up to 30 million (May, 1988; Wilson, 1988). Knowledge of taxonomy is critical for understanding diversity. This is the field of
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