SPECIES COEXISTENCE AND SELF-ORGANIZING SPATIAL DYNAMICS

IN a patchy environment, dispersal between neighbouring local populati ons can allow the total (regional) population to persist(1-5); even wh ere all patches are identical and the within-patch dynamics are unstab le, the total population readily persists as a metapopulation. This pe rsistence is associated with striking, self-organized spatial patterns in the densities of the subpopulations. In the case of hosts and para sitoids, these may form spiral waves, spatial chaos, or a so-called 'c rystal lattice' with regularly spaced knots of high population density (4'6). Here we extend earlier work on two species to three or more, sh owing that coexistence of competing species is usually associated with some degree of persistent spatial segregation, even when the environm ent is uniform. At its most extreme, this can confine one species to s mall, relatively static 'islands' within the habitat, giving the appea rance 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 facto rs.