Ecological speciation occurs in saturated floras as well as in unsaturated floras. Whereas much consideration has been given to ecological divergence in open habitats, the process of niche shifting in highly competitive environments hardly has been discussed. I propose that ecological speciation in relatively saturated communities is facilitated by disturbance, which relaxes the competitive pressures on populations entering a new habitat. Disturbance affords marginally adapted immigrants an opportunity to become established and form reproducing populations. These populations then may respond to local selective pressures for greater adaptedness, thereby placing them on a speciation trajectory. This conceptual model is bolstered by the role of disturbance in facilitating the invasion of communities by new entities, as is well documented in the literature on alien species.