Survival, opportunism and convenience in the processes of cave colonization by terrestrial faunas

Modern discoveries of cave-restricted animals in many tropical limestone areas, in lava tubes and other non-­calcareous caves, and in subterranean non-cave habitats, have led us to reconsider classic interpretations of cave colonization processes, which were mainly based on the direct influence of Pleistocene climatic changes. The relict concept (for cave species) and the refuge concept (for caves) have lost their value as paradigms, and cave colonization directly deterrnined by Pleistocene glaciations should rather be considered as a localized model. Organisms can colonize caves for a variety of reasons, including survival (caves as immediate refuges), opportunism (caves as virgin spaces to be colonized) or convenience (caves as escape valves when new competitive pressures appear in surface habitats). All these styles of colonization can be well exemplified in temperate areas which suffered the direct impact of Pleistocene glaciations. However, all of them can also be postulated in other situations which have nothing to do with climatic revolutions.