BASIN BOUNDARY COLLISION AS A MODEL OF DISCONTINUOUS CHANGE IN ECOSYSTEMS

Abstract

It has long been recognized that gradual secular changes in environmental parameters may lead to discontinuous changes in ecosystems. The dominant model ex- plaining such changes has been the presence of alternative attractors and their basins. We discuss a related model, that of basin boundary collisions, that may also produce discon- tinuous changes in an environmental variable. The alternative model suggests that the underlying structure of the basins themselves may be gradually changed by the changing environmental factor. Consequently, the basin of the chaotic attractor may disappear, because it intersects the alternative basin; hence the term basin boundary collision. The implications of this model can be dramatic, such as sudden and unpredictable extinctions or dramatic and unexpected changes in ecosystem syndromes. Furthermore, where this model applies, ancillary phenomena such as a lag in time of the ecosystem change or the existence of so- called chaotic transients may be important. Also discussed are the implications of these results in a world in which slowly changing forcing parameters are well known (e.g., gradual increases of CO2 in the atmosphere, and gradual changes in political attitudes about con- servation).