COMPETITION AND COEXISTENCE - MODELING APPROACHES

Competition and coexistence are discussed in the framework of multispecies and simple food web models. A class of models is defined where for steady state solutions the principle of competitive exclusion acts. With variable environments, however, the same class of models allows coexistence of many species. The coexisting species have to fulfil a qualitative trade-off condition (improvement of one property is accompanied by detoriation of another). In the case of periodic environments a new definition of fitness is introduced. The variability, which is a prerequisit for coexistence in these models, does not necessarily have to be externally forced on the system. Also internally created temporal and spatial self-organized structures enhance the possibilities for coexistence of competing species. Many relatively simple models illuminate the mechanisms leading to persistent coexistence. The models are formulated such that inter- and intraspecific interactions of the many species occur via few collective variables. An extended class of models takes species internal variables into account.