The Ecological Classification of Cave Animals and Their Adaptations

Abstract

During the earliest studies of cave biology, researchers soon recognized that anjmal species living permanently in caves often shared a suite of similar morphological features, even when only distantly related (Racovitza 1907; VandeI 1964). The most notable features are the loss or reduction of structures normally considered necessary for life, such as eyes, bodily color, and robustuess. To better understand cave ecology, early workers attempted to classify cave animals by correlating the different degrees of morphological change with the observed levels of their association with caves. However, the high variability in morphology displayed by caveruicoles, lack of ecological data for most species, and the subjective nature inherent in determining their status in caves make ecological classification of some species problematic. One of the earliest attempts tu classify cave animals was presented by the Danish biologist Schil1ldte (1849). He proposed four levels or categories distinguished by the amount of light and the nature of the walls in the preferred hahitat: (I) shadow animals (Skygge-Dyr), (2) twilight animals (Tusmorke-Dyr), (3) obscure area animals (Hule-Dyr), and (4) obscure area with flowstone animals (Drypsteenshule-Dyr). Later, Schiner (1854) visiting several caves in southeastern Europe recognized three categories of cave animals based on their ethology: (I) occasional hosts, animals encountered in caves but also living in surface habitats; (2) troglophiles, animals inhabiting regions where daylight still penetrates but which can be rarely encountered on the surface; and (3) troglobionts, animals living exclusively in caves