ONCE upon a time, ecologists talked of the “balance of nature”. It seemed that any small fluctuation in an ecological system was always balanced out by some other change, maintaining equilibrium even in complex situations. Though a seductive idea, it was finally killed off in the 1960s by the American social scientist Herbert Simon, who studied complex systems and concluded that it is in fact the simplest that tend to survive. (New Scientist editorial, p.3, 13 August 2011)
Herbert Simon hardly killed off the idea of a balance of nature. In practice, the idea continues to be invoked widely, whether in the form that nature’s complex ecosystems are fragile and so need to be treated carefully or are models for how complex productive systems can run and so need to be conserved. In theory, all Simon showed was that an engineer has a better chance of building a stable complex system if it is simple in the sense of being made up of weakly interconnected modules. His theoretical result is not, however, relevant to ecology where systems are not engineered, but develop over time through in-migration and turnover of the species making up the system. Indeed, by mimicking such successional processes, it is quite easy to build stable mathematical models that have much richer interactions than Simon’s modular system (see Chapter 1 of P. J. Taylor, Unruly Complexity: Ecology, Interpretation, Engagement Chicago: University of Chicago Press, 2005).