The isolation of cave ecosystems from dynamic surface environments gives them relatively stable conditions, allowing underlying features of the cave, such as geochemistry, hydrology and microbial biogeochemical cycling to be the driving influences on the composition of microbial niches within cave ecosystems. The transfer of gases, either geological or biogenic, is of particular importance in these subterranean ecosystems, as they represent not only a source of oxygen but also a major source of carbon and energy.