ill-coordinated responses to changes in ecosystems may not be intrusive until much time has elapsed.

In ecological systems, one form of information feedback is coevolution, a term first used by Ehrlich and Raven (1964) in examining the evolution of plants and the insects that feed on them. They defined coevolution as a pair-wise process in which the appearance of a trait in one species elicits a response in another species. For example, increased speed in a carnivorous mammal may result in increased speed in its prey, or a variety of other adaptations to offset the predator's speed, such as improved camouflage. Futuyama and Slotkin (1983) indicated that development of a particular trait in one or more species may result in a suite of traits in several other species. Ghersa et al. (1994) described the coevolution of agroecosystems and weed management. They postulate that weed-management practices have become closely linked to social and economic, rather than biological, factors. As Harlan and deWet (1965) have noted, weeds and weed problems are anthropocentric terms applied to populations of plants when they are considered undesirable.

Before the agricultural revolution, the needs of Homo sapiens were met in ways not dramatically different from the ways in which needs of other species were met. Human populations were comparatively small and kept from the explosive growth of the past century by disease, starvation, and even predation. These are, in fact, much the same population control factors affecting other species. Throughout history, ecosystems provided all the services necessary for the continuation of the human species: breathable air, potable water, food, and a consistent climate over the short-term. Now human society has a codependence on both a technological life-support system and an ecological life-support system. However, the maintenance needs of technological services get much more attention than those of ecosystem services. In a very real sense, natural systems and human systems are coevolving since only those opportunistic and communal species tolerant of the anthropogenic alterations of natural systems are likely to thrive. These may be opportunistic species resistant to pesticides and habitat fragmentation and tolerant of a wide range of ecological conditions—in short, pests.

Those species that are tolerant of anthropogenically changed conditions might provide some of the services that more complex natural ecosystems provided previously. However, it seems unlikely that they will perform in precisely the same ways. Kauffman (1993) proposes a bold hypothesis: complex, adaptive systems operate on the edge of chaos. He feels that not only organisms, but economic entities and nations, do not simply evolve, but rather coevolve, and that coevolving complex systems mutually operate at the edge of chaos. If the adapting system is itself in the ordered (rather than the chaotic or boundary) regime, Kauffman (1991, 1993) believes the system itself adapts on a smooth landscape (see Holling, in this volume). In the chaotic regime, the system adapts on a very rugged landscape, and, of course, in the boundary regime, it is intermediate.



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