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Caves provide a home for many unique biological features. Cave ecologies are very diverse, and not sharply distinct from surface habitats. Generally however, the deeper the cave becomes, the more rarefied the ecology.

Cave ecosystems are very fragile. Because of their rarity and position in the ecosystem they are threatened by a large number of human activities. Dam construction, limestone quarrying, water pollution and logging are just some of the disasters that can devastate or destroy underground biological communities.

Cave environments

Endogean: the parts of caves that are in communication with surface soils through cracks, rock seams, groundwater seepage and root protrusion.

Parahypogean: the threshold regions near cave mouths that extend to the last penetration of sunlight.

Hypogean: the 'true' cave environments. These can be in regular contact with the surface via wind and underground rivers, or the migration of animals, or can be almost entirely isolated. Deep hypogean environments can host autonomous ecologies whose primary source of energy is not sunlight, but chemical energy liberated from limestone and other minerals by bacteria.

Cave organisms

Troglobites ('cave dwellers') are obligatory cavernicoles, specialised for cave life. Some can leave caves for short periods and may complete parts of their life cycles above ground, but cannot live their entire lives outside of a cave. Examples include chemotrophic bacteria, some species of flatworms, collembola and blindfish.

Troglophiles ('cave lovers') can live part or all of their lives in caves, but can also complete a life cycle in appropriate environments on the surface. Examples include cave crickets, millipedes, pseudoscorpions and spiders.

Trogloxenes ('cave guests') frequent caves, and may require them for a portion of their life cycle, but must return to the surface (or a parahypogean zone) for at least some portion of its life. Hibernating reptiles and mammals are the most widely recognised examples.

There are also so-called accidental trogloxenes which are surface organisms that enter caves for no survival reason. Some may even be troglophobes ('cave haters'), which cannot survive in caves for any extended period. Examples include deer that fell through a sinkhole, frogs swept into a cave by a flash flood, etc.

Limitations to cave ecology

The two factors that limit cave ecologies are generally energy and nutrients. To some degree moisture is always available in actively-forming karst caves. Cut off from the sunlight and steady deposition of plant detritus, caves are poor habitats in comparison with wet areas on the surface. The majority of energy in cave environments comes from the surplus of the ecosystems outside. One major source of energy and nutrients in caves is dung from trogloxenes, the majority of which is deposited by bats. You’ll find a lot of bat life in Oman’s caves.