The Matching of Disciplines from the Sciences with Disciplines of Engineering, Showing the Correspondence between the Two Activities

Scientific Field or Topic Engineering Field

Chemistry Chemical engineering

Mechanics Mechanical engineering

Electricity Electrical engineering

Ecology Ecological engineering also are based on particular scientific disciplines or topics (Table 1.2). The principles and theories of ecology are fundamental for understanding natural ecosystems and, therefore, also for the design, construction, and operation of new ecosystems for human purposes. The ecosystem is the network of biotic (species populations) and abiotic (nutrients, soil, water, etc.) components found at a particular location that function together as a whole through primary production, community respiration, and biogeochemical cycling. The ecosystem is considered by some to be the fundamental unit of ecology (Evans, 1956, 1976; J0rgensen and Muller, 2000; E. P. Odum, 1971), though other units such as the species population are equally important, depending on the scale of reference. The fundamental nature of the ecosystem concept has been demonstrated by its choice as the most important topic within the science in a survey of the British Ecological Society (Cherrett, 1988), and E. P. Odum chose it as the number one concept in his list of "Great Ideas in Ecology for the 1990s" (E. P. Odum, 1992). Reviews by Golley (1993) and Hagen (1992) trace the history of the concept and provide further perspective.

Functions within ecosystems include (1) energy capture and transformation, (2) mineral retention and cycling, and (3) rate regulation and control (E. P. Odum, 1962, 1972, 1986; O'Neill, 1976). These aspects are depicted in the highly aggregated P-R model of Figure 1.2. In this model energy from the sun interacts with nutrients for the production (P) of biomass of the system's community of species populations. Respiration (R) of the community of species releases nutrients back to abiotic storage, where they are available for uptake again. Thus, energy from sunlight is transformed and dissipated into heat while nutrients cycle internally between compartments. Control is represented by the external energy sources and by the coefficients associated with the pathways. Rates of production and respiration are used as measures of ecosystem performance, and they are regulated by external abiotic conditions such as temperature and precipitation and by the actions of keystone species populations within the system, which are not shown in this highly aggregated model. Concepts and theories about control are as important in ecology as they are in engineering, and a review of the topic is included in Chapter 7.

Ecosystems can be extremely complex with many interconnections between species, as shown in Figure 1.3 (see also more complex networks: figure 6 in Winemiller, 1990 and figure 18.4 in Yodzis, 1996). Boyce (1991) has even suggested that ecosystems "are possibly the most complex structures in the universe." Charles

FIGURE 1.2 Basic P-R model of the ecosystem. "P" stands for primary production and "R" stands for community respiration.

Elton, one of the founders of modern ecology, described this complexity for one of his study sites in England with a chess analogy below (Elton, 1966; see also Kangas, 1988, for another chess analogy for understanding ecological complexity):

In the game of chess, counted by most people as capable of stretching parts of the intellect pretty thoroughly, there are only two sorts of squares, each replicated thirty-two times, on which only twelve species of players having among them six different forms of movement and two colours perform in populations of not more than eight of any one sort. On Wytham Hill, described in the last chapter as a small sample of midland England on mostly calcareous soils but with a full range of wetness, there are something like a hundred kinds of "habitat squares" (even taken on a rather broad classification, and ignoring the individual habitat units provided by hundreds of separate species of plants) most of which are replicated inexactly thousands of times, though some only once or twice, and inhabited altogether by up to 5000 species of animals, perhaps even more, and with populations running into very many millions. Even the Emperor Akbar might have felt hesitation in playing a living chess game on the great courtyard of his palace near Agra, if each square had contained upwards of two hundred different kinds of chessmen. What are we to do with a situation of this magnitude and complexity? It seems, indeed it certainly is, a formidable operation to prepare a blueprint of its organization that can be used scientifically.

A variety of different measures have been used to evaluate ecological complexity, depending on the qualities of the ecosystem (Table 1.3). The most commonly used measure is the number of species in the ecosystem or some index relating the number of species and their relative abundances. Complexity can be overwhelming and it can inhibit the ability of ecologists to understand ecosystems. Therefore, very simple ecosystems are sometimes important and useful for study, such as those found in the hypersaline conditions of the Dead Sea or Great Salt Lake in Utah, where high salinity stress dissects away all but the very basic essence of ecological structure



FIGURE 1.3 Diagram of a complex ecosystem. (From Abrams, P. et al. 1996. Food Webs: Integration of Patterns and Dynamics. Chapman & Hall, New York. With permission.)

and function. E. P. Odum (1959) described the qualities of simplicity in the following quote about his study site in the Georgia saltmarshes:

The saltmarshes immediately struck us as being a beautiful ecosystem to study functionally, because over vast areas there is only one kind of higher plant in it and a relatively few kinds of macroscopic animals. Such an area would scarcely interest the

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