The coexistence of species within a community generally can be explained by niche differentiation, mechanisms that control competitive displacement, and by chance. This review is an attempt to link ecological conceptual models with results from field research. A verification of different theoretically developed mechanisms shows that niche differentiation plays a major role in the Antarctic. This is particularly true if a broad niche definition is applied that includes alternating phases of competitive strength and weakness that allow populations to persist in a community. Such specific adaptation to the environment also seems to be an important mechanism among animals, which, to date, have been assumed to have broadly overlapping ecological demands. Nevertheless, disturbances due to glaciation history, ice impact, and predation, as well as a high dispersal capacity and low resource limitation contribute to the coexistence or, locally, to the reduction of potential competitors. Chance, reflecting extremely complex or otherwise indecipherable processes, also shapes diversity, e.g., during recolonization after habitat devastation due to iceberg scouring. The slow rates of ecological processes in the Antarctic benthos are shown not necessarily to reduce, but perhaps, to increase the potential for evolutionary radiation in some systematic groups. The fundamental question of how ecosystems continue to develop in the presence or absence of anthropogenic impacts can only be answered if such system-specific ecological and evolutionary mechanisms can be better identified and verified. Studies of the Antarctic benthos can contribute to a corresponding global approach if more comparable information on the life histories of representative species becomes available and if ecological models are developed to decipher complex processes, that shape biodiversity patterns. © 2006 Elsevier Ltd. All rights reserved.