The Ecological Classification Of Cave Animals And Their Adaptations

Why certain animals lose features believed essential, like eyes, bodily color, and robustness, to live permanently underground has long intrigued biologists and laymen. Many of these features evolved independently and shared among diverse groups living in caves including both terrestrial and aquatic cavernicoles. The degree of change often correlates with the level of association of the species to caves. This association allowed development of a classification scheme to help understand the evolutionary ecology of cave communities. The refined scheme, called the Schiner-Racovitza system, is based on both morphology and ecology. The categories are troglobionts and stygobionts (animal species that obligately live underground on land or in water, respectively), troglophiles (animals that can live and reproduce in both underground and surface habitats), and trogloxenes (animals that regularly visit caves for food or refuge). Common adaptations to cave life involve morphology, behavior, and physiology. In addition to the conspicuous losses, many compensatory traits have evolved, such as longer appendages, longer and more slender body, more and larger sensory structures, and specialized mouthparts and tarsi. Modified behavioral traits include reduction in circadian rhythm, reduced dispersal ability, slower but nearly continuous activity, and modified mating behavior. Physiological adaptations include low metabolism rate, dietary changes, resistance to starvation, modified water balance mechanisms, tolerance to high CO2 and low O2, and increased longevity. Cave-adapted animals also display greater K-selection with fewer and larger eggs and reduced life cycle.