Comparison of Machine Analogies in Ecology
Machine Analogy Ecological System Modelled Reference
Block-and-springs Conveyor belt Pin ball machine Connected gears Chemical reactor Cannon-ball catcher
Freshwater plankton food chain Population dynamics Population dynamics Marine plankton food chain Oceanic biogeochemistry Euphotic zone of ecosystems
Leavitt, 1992 Oster, 1974 Pearson, 1960
Clarke, 1946; Margalef, seen in Odum, 1983
Thus, engineering control theory was specifically developed for systems that have been designed by humans. Because engineering control theory does not apply to ecosystems, fundamental differences must exist between these two kinds of systems. Berryman et al. (1992) also suggest that engineering control theory "should evolve to meet the needs and terminology of the ecologist."
Even though engineering ideas of control have not provided much new insight in ecology, they are useful in order to contrast the degree of difference in understanding about control between the two fields. There is no general theory of control in ecology, unlike in engineering. Perhaps new generations of ecological engineers with balanced training and experience in both disciplines will be able to make contributions to the academic field of ecology about the nature of control in an ecosystem context. Possible directions are outlined by Conrad (1976) and Hannon (1986; Hannon and Bentsman, 1991). E. P. Odum (1997) suggested that ecologists should shift emphasis from the tight control homeostasis of to homeorhesis, which is a looser form of control, for ecological studies above the organismal level of organization.
An interesting aside to the discussion of control ideas in ecology and engineering is the role of the machine analogy. Machines or mechanical devices, which have obvious relations to engineering, have long been used as analogies to help understand complex living systems. Calow (1976), Channell (1991), and Grmek (1972) reviewed the history of this subject which is filled with fascinating examples such as the importance of the development of the mechanical clock to theories of biology during the Renaissance. Unlike these historical references, mechanical analogies have seldom been useful in explaining ecology. Examples are given in Table 7.4, but none are well known. Clarke's (1946) gear diagram is perhaps most noteworthy (Figure 7.12). Here gears in the mechanism represent different trophic levels, which are scaled to turn at different speeds depending on production rates. H. T. Odum (1950) elaborated on the gear analogy in a section of his dissertation entitled "A Biosphere of Cogwheels," citing Clarke's paper (see also Figure 8.7 in H. T. Odum and E. C. Odum, 1976). Even though he also once used a gear model of a food web in his earlier work (see H. T. Odum, 1983, Figures 15-24), Margalef (1985) offers an explanation for this general lack of success of the mechanical analogy in ecology in the following quote:
Radiant Energy: 3,000,000 g-cal/day
FIGURE 7.12 Example of a machine analogy from ecology. (From Clarke, G. L. 1946. Ecological Monographs. 16:321-335. With permission.)
The essence of the ecosystem is the pattern that links its components. The a priori freedom of behavior of each of the parts is more or less diminished when the parts join the system. But the elements retain some flexibility or elasticity, because of time delays at the junctions. Ecosystems behave in just this way, being made up of individuals of a certain size, of behavior more less unpredictable, and out of equilibrium most of the time.
The ecosystem is not a rigid machine made of gears and levers, but involves more costly transmission of information across a fluid (and turbulent) environment. In one sense it is comparable to a Turing machine, an automaton able to read information from a tape, and to use it for any purpose, including writing it on to a new tape, or for building the machines. However, it makes little sense to keep separate the instructions to build the machines, to operate them, or to process and pass information to other machines. The blurring of proper distinctions between operative parts and memories makes organisms and ecosystems quite different from computers, and this has to be kept in mind in formulating ecosystem models. They cannot be rigid clockwork.
Ulanowicz (1993, 1997) provides an even stronger critique of the machine analogy in ecology. He even suggests that mechanistic (machinelike) explanations are inadequate, and he calls for a post-Newtonian ecology with alternative concepts of causality. While these criticisms have merit and need to be explored, ecological engineering brings a renewed interest to the machine analogy. John Todd's living machines (see Chapter 2) and Robert Kadlec's (1997) "biomachine" treatment wet lands are hybrid systems. Todd's work in particular goes beyond the use of machine as analogy in development of design knowledge for hybrid systems. His work on living machines is somewhat reminiscent of the work of Franz Reuleaux, the German engineer who is credited with developing the fundamental theory of machine design in mechanical engineering in the late 1800s (O'Brien, 1964). At an elemental level, design of complex machines consists of combinations of the five basic "simple machines": the lever, the wheel and axle, the pulley, the wedge, and the screw. Reuleaux developed principles and algorithms for machine design based on kinematics, which is the science of motion. Thus, the simple machines are combined in such a way that their coordinated motion results in the transformation of energy and the output of useful work. Todd's design of living machines represents a kind of kinematics for ecological engineering that is both effective and elegant. Concepts of both machine and ecosystem are needed for the design of the new living machines. Ideas of the ecosystem as a computer and succession as a form of computation (see Chapter 5) are possible examples of new directions for the machine analogy in ecology. Technoecosystems are discussed as a future direction in Chapter 9. An interesting nexus may emerge as the field of ecological engineering develops among the machine analogs in ecology, the living machine concept, and the theory of self-reproducing machines (see Chapter 3).
At least two management fields exist which involve actual ecological control through manipulation of species. The field of biological control is well established in agriculture (Batra, 1982; Debach, 1974; Murdoch and Briggs, 1996; National Research Council, 1996), involving the introduction of predators, parasites, or diseases for pest population control. This is a population scale approach that is implemented to reduce the use of chemical pesticides. Although well established, the field is coming under greater scrutiny because of the risks of biological control agents becoming invasive (Simberloff and Stiling, 1996). Biomanipulation is an ecosystem scale approach to control of eutrophication in lakes (Kitchell, 1992; Reynolds, 1994). This field was first outlined by Shapiro et al. (1975), and it involves manipulating piscivore (fish predators) abundance to reduce phytoplankton abundance and to improve water clarity. Biomanipulation is based on the trophic cascade model discussed earlier and, like this model, remains controversial (Carpenter and Kitchell, 1992; DeMelo et al., 1992). However, the advocates of biomanipulation are ambitious as noted in the quote by Carpenter et al. (1985) given below:
The concept of cascading trophic interactions links the principles of limnology with those of fisheries biology and suggests a biological alternative to the engineering techniques that presently dominate lake management. Variation in primary productivity is mechanistically linked to variation in piscivore populations. Piscivore reproduction and mortality control the cascade of trophic interactions that regulate algal dynamics. Through programs of stocking and harvesting, fish populations can be managed to regulate algal biomass and productivity.
Drenner and Hambright (1999) reviewed 41 biomanipulation trials and found that 61% were successful at improving water quality.
The fields of biological control and biomanipulation represent examples of the concept of "ecological engineering through control species" that was introduced by H. T. Odum (1971). Berryman et al. (1992) also advocate ecological engineering through species manipulation in the following quote:
Natural ecosystems contain a plethora of feedbacks between their biotic components; for example, negative feedbacks between predators and prey and positive feedbacks between competing species. The ecological control engineer can, theoretically, manipulate these feedbacks in an attempt to regulate the system at desired steady states or to amplify certain components.
Unlike other examples of ecological engineering, manipulation of control species involves no familiar hardware such as pumps and pipes or electrical circuits. It is more analogous to the new discipline of software engineering, with manipulations of information rather than energy and materials. This may be the most sophisticated form of ecological engineering and will require much more experience in order to achieve success, as opposed to other applications discussed in earlier chapters where successful progress is established and growing.
In conclusion, invasive exotic species are an example of biology that is "out of control." On the one hand this may be thought of negatively as in the story of Frankenstein, where exotics represent the monster turned loose on the innocent villagers. It is interesting to note that this same fear occurs with certain forms of modern technology that exceed their intended functions (Winner, 1977). Tenner (1997) describes many of these examples in his book entitled Why Things Bite Back: Technology and the Revenge of Unintended Consequences." Bill Joy presents an even stronger case for the potential dangers of genetic engineering nanotechnology and robotics, which he refers to as the GNR technologies because these technologies are capable of self-reproduction, Joy (2000) warns that "they can spawn whole new classes of accidents and abuses" (see Crichton, 2002 for a science fiction interpretation). On the other hand, the idea of being "out of control" may be an example of a higher level phenomenon where new forms of order emerge out of old systems (Kelly, 1994). Rodney Brooks has also written on the positive aspects of being out of control. Control mechanisms require extra energy input for maintenance. If a system can be designed that does not require control (i.e., one that is out of control), then energy can be saved and used for other productive purposes. Brooks (2002; Brooks and Flynn, 1989) has explored this concept by desigining and building simple robots that achieve complex tasks through collective, emergent behavior (See Chapter 3). In a sense, the design of all ecologically engineered systems is "out of control" to some extent because of the contributions of self-organization. For example, the restoration ecologist may try to achieve a certain species composition in a restored marsh through intentional plantings but the final plant community is different because of natural selection and the addition of volunteer species that disperse in from the surrounding landscape. Thus, ecological engineers must be able to give up some control over their designs in order to create them. This represents a new kind of design paradigm for engineering, which is actively evolving as noted by the many examples given in this text. How much control are ecological engineers willing and able to give up in order to "design" new systems? The self-organization that is taking place with invasive exotic species may be a guide. In fact, the best way to conserve biodiversity may be to maximize dispersal and invasion globally. Instead of allowing a subset of highly preadapted species to homogenize the biosphere, more species may be supported by accelerating the dispersal processes. For example, species endangered in the U.S. might flourish in China and vice versa. In this way humans give up control in order to create a more diverse planet. Perhaps humanity needs both preserves (i.e., national parks), where the old ecosystems without exotics are maintained with care and at high cost, and new systems, where exotic species and native species are actively and intentionally mixed together. These new systems might be called mixing zones where self-organization is encouraged in order to save species and to create useful ecosystem designs. This may happen anyway, whether or not humans wish it to happen. Perhaps ecological engineers are best prepared by their balanced training to study these ideas and to be leaders in encouraging a new order of biodiversity.
APPENDIX 1: LIST OF BOOKS PUBLISHED ON EXOTIC SPECIES USED TO PRODUCE FIGURE 7.1
Elton, C. S. 1958. The Ecology of Invasions. Methuen, London.
Laycock, G. 1966. The Alien Animals. Ballantine Books, New York.
Mead, A. R. 1961. The Giant African Snail: A Problem in Economic Malacology. University of Chicago Press, Chicago, IL.
Mann, R. (ed.). 1979. Exotic Species in Mariculture. MIT Press, Cambridge, MA.
Roots, C. 1976. Animal Invaders. Universe Books, New York.
Silverstein, A. and V. Silverstein. 1974. Animal Invaders. Atheneum, New York.
Courtenay, W. R., Jr. and J. R. Stauffer, Jr. (eds.). 1984. Distribution, Biology, and Management of Exotic Fishes. Johns Hopkins University Press, Baltimore, MD.
Dahlsten, D. L. and R. Garcia (eds.). 1989. Eradication of Exotic Pests. Yale University Press, New Haven, CT.
Drake, J. A., H. A. Mooney, F. di Castri, R. H. Groves, F. J. Kruger, M. Rejmanek, and M. Williamson (eds.). 1989. Biological Invasions: A Global Perspective. John Wiley & Sons, Chichester, U.K.
Druett, J. 1985. Exotic Intruders: The Introduction of Plants and Animals into New Zealand. Heinemann, Auckland, New Zealand.
Groves, R. H. and J. J. Burdon (eds.). 1986. Ecology of Biological Invasions. Cambridge University Press, Cambridge, U.K.
Hengeveld, R. 1989. Dynamics of Biological Invasions. Chapman & Hall, London.
Long, J. L. 1981. Introduced Birds of the World. Universe Books, New York.
Macdonald, I. A. W., F. J. Kruger, and A. A. Ferrar (eds.). 1986. The Ecology and Management of Biological Invasions in Southern Africa. Oxford University Press, Cape Town, South Africa.
Mooney, H. A. and J. A. Drake (eds.). 1986. Ecology of Biological Invasions of North America and Hawaii. Springer-Verlag, New York.
Thomas, L. K., Jr. 1980. The Impact of Three Exotic Plant Species on a Potomac Island. National Park Service Scientific Monograph Series No. 13, U.S. Dept. of the Interior, Washington, DC.
Wilson, C. L. and C. L. Graham (eds.). 1983. Exotic Plant Pests and North American Agriculture. Academic Press, New York.
Bright, C. 1998. Life Out of Bounds: Bioinvasion in a Borderlesss World. W. W. Norton, New York.
Cox, G. W. 1999. Alien Species in North America and Hawaii. Island Press, Washington, DC.
Cronk, Q. C. B. and J. L. Fuller. 1995. Plant Invaders. Chapman & Hall, London.
Devine, R. 1998. Alien Invasion. National Geographical Society, Washington, DC.
de Waal, L. C., L. E. Child, P. M. Wade, and J. H. Brock (eds.). 1994. Ecology and Management of Invasive Riverside Plants. John Wiley & Sons, Chichester, U.K.
Di Castri, F., A. J. Hansen, and M. Debussche (eds.). 1990. Biological Invasions in Europe and the Mediterranean Basin. Kluwer Academic, Dordrecht, The Netherlands.
D'Itri, F. M. (ed.). 1997. Zebra Mussels and Aquatic Nuisance Species. Ann Arbor Press, Chelsea, MI.
Goldschmidt, T. 1996. Darwin's Dreampond. S. Marx-Macdonald (Trans.). MIT Press, Cambridge, MA.
Groves, R. H. and F. di Castri (eds.). 1991. Biogeography of Mediterranean Invasions. Cambridge University Press, Cambridge, U.K.
Jaffe, M. 1997. And No Birds Sing: The Story of an Ecological Disaster in a Tropical Paradise. Barricade Books, New York.
Johnston, R. F. and M. Janiga. 1995. Feral Pigeons. Oxford University Press, New York.
Lesinski, J. M. 1996. Exotic Invaders. Walker and Co., New York.
Lever, C. 1994. Naturalized Animals: The Ecology of Successfully Introduced Species. T & A D Poyser, London.
Luken, J. O. and J. W. Thieret (eds.). 1997. Assessment and Management of Plant Invasions. Springer, New York.
Mayer, J. J. and I. Lehr Brisbin, Jr. 1991. Wild Pigs of the United States. University of Georgia Press, Athens, GA.
McKnight, B. N. (ed.). 1993. Biological Pollution. Indiana Academy of Science, Indianapolis, IN.
Meinesz, A. 1999. Killer Algae. D. Simberloff (Trans). University of Chicago Press, Chicago, IL.
Nalepa, T. F. and D. W. Schloesser (eds.). 1993. Zebra Mussels. Lewis Publishers, Boca Raton, FL.
National Research Council. 1996. Stemming the Tide. National Academy Press, Washington, DC.
Office of Technology Assessment (OTA). 1993. Harmful Non-Indigenous Species in the United States. OTA-F-565. U.S. Government Printing Office, Washington, DC.
Pitcher, T. J. and P. J. B. Hart (eds.). 1995. The Impact of Species Changes in African Lakes. Chapman & Hall, London.
Pysek, P., K. Prach, M. Rejmanek, and M. Wade (eds.). 1995. Plant Invasions: General Aspects and Special Problems. SPB Academic Publ., Amsterdam, The Netherlands.
Ramakrishnan, P. S. 1991. Ecology of Biological Invasions in the Tropics. International Scientific Publications, New Delhi, India.
Randall, J. M. and J. Marinelli (eds.). 1996. Invasive Plants. Brooklyn Botanic Garden, New York.
Rodda, G. H., Y. Sawai, D. Chiszar, and H. Tanaka (eds.). 1999. Problem Snake Management, the Habu and the Brown Treesnake. Comstock Publ. Associates, Ithaca, NY.
Rosenfield, A. and R. Mann (eds.). 1992. Dispersal of Living Organisms into Aquatic Ecosystems. Maryland Sea Grant Publ., College Park, MD.
Shigesada, N. and K. Kawasaki. 1997. Biological Invasions: Theory and Practice. Oxford University Press, Oxford, U.K.
Simberloff, D., D. C. Schmitz, and T. C. Brown (eds.). 1997. Strangers in Paradise. Island Press, Washington, DC.
Stone, C. P., C. W. Smith, and J. T. Tunison (eds.). 1992. Alien Plant Invasions in Native Ecosystems of Hawaii. University of Hawaii Cooperative National Park Resources Studies Unit, Honolulu, HI.
Williams, D. F. (ed.). 1994. Exotic Ants. Westview Press, Boulder, CO.
Williamson, M. 1996. Biological Invasions. Chapman & Hall, London.
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