The purpose of this study was to: (a) obtain baseline data on the colonization of artificial islands in a closed laboratory system; (b) investigate effects of island area and distance from an epicenter (source of protozoa) on the colonization process, and (c) test the effect of the maturity of an epicenter on the colonization of surrounding islands. Islands which were smallest in area or closest to the epicenter had significantly greater species richness during the 7 days of the experiments. Islands exposed to epicenters of intermediate maturity had significantly greater species richness than islands tested with mature (fully colonized) epicenters. Evidence gathered thus far strongly suggests that kinds of species present during different periods of colonization are responsible for differences in species richness on islands exposed to epicenters of different maturities.