and communities of organisms most resistant to this stress, with an equal selection for pioneering species capable of taking advantage of chaos. More than 100 years ago, Kew (1893) provided an eerie insight into the kinds of species that would coevolve with human society if hostile coevolution continues. He described the durability and colonizing potential of Dreissena (the zebra mussel), which relatively recently became a major problem in North America (Ludyanskiy et al., 1993), as follows:

The Dreissena is perhaps better fitted for dissemination by man and subsequent establishment than any other fresh-water shell; tenacity of life, unusually rapid propagation, the faculty of becoming attached by string byssus to extraneous substances, and the power of adapting itself to strange and altogether artificial surroundings have combined to make it one of the most successful molluscan colonists in the world.

Thus, even if ecological losses or problems can be predicted, it seems as though society is often willing to trade these problems for jobs, particularly in uncertain economic times (i.e., during recessions). Pratt and O'Connor (1994) describe a situation at Gettysburg Historic Park, where certain conditions that existed at the time of Pickett's charge across a cornfield were to be maintained for historical reasons. The cornfield was located between two lines of trees. During the Civil War, only a few deer inhabited the area. Deer were controlled by hunters, who could harvest a substantial percentage of the population. At that time, deer were not protected either by legislation or by being adjacent to areas where hunting would be highly objectionable. For many years, farmers were willing to pay a modest fee to grow corn in this historic area because they could harvest enough to make a profit. Eventually, the deer herd expanded to a size that made harvesting corn no longer profitable. In addition, harvesting the deer at the necessary rate was objectionable to components of society for a variety of reasons. Replacing the cornfield with astroturf or some other nonhistoric condition was also unacceptable. Under the best circumstances, a substantial expenditure would be necessary to preserve the historic condition of the area by excluding the deer. Consequently, the coevolution of the deer herd and human society became more and more expensive with no socially acceptable alternative in view. In this example, the natural control measures regulating the deer population were removed and resulted in densities unlikely to have been achieved previously in natural systems. All this occurred because humans provided an extraordinary food base and freedom from predation for the deer.

Chaos at the interface can be manifested in a variety of ways. A contrasting illustration for an aquatic system is the invasion of North America by the Asiatic clam, the zebra mussel, and the quagga mussel (Russian mollusc, D. bugensis). These invaders from different parts of the world might well have taken hold in pristine systems in North America had they been able to get there. However, without the help of human society's transportation system, this would have been

The National Academies of Sciences, Engineering, and Medicine
500 Fifth St. N.W. | Washington, D.C. 20001

Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement