SPECIES COEXISTENCE AND SELF-ORGANIZING SPATIAL DYNAMICS

IN a patchy environment, dispersal between neighbouring local populations can allow the total (regional) population to persist(1-5); even where all patches are identical and the within-patch dynamics are unstable, the total population readily persists as a metapopulation. This persistence is associated with striking, self-organized spatial patterns in the densities of the subpopulations. In the case of hosts and parasitoids, these may form spiral waves, spatial chaos, or a so-called 'crystal lattice' with regularly spaced knots of high population density(4'6). Here we extend earlier work on two species to three or more, showing that coexistence of competing species is usually associated with some degree of persistent spatial segregation, even when the environment is uniform. At its most extreme, this can confine one species to small, relatively static 'islands' within the habitat, giving the appearance of isolated pockets of favourable habitat. The distributions of interacting species may thus result from a trade-off between dispersal and competition within subpopulations, as much as from external factors.