Abstract
Subterranean fauna can be divided into two broad groups – stygofauna are aquatic and occur in groundwater, while troglofauna are air-breathing and occur in the unsaturated zone from depths of a metre or so below the ground surface down to the water table. Defining exactly which species are covered by the term subterranean fauna is quite complex, because of the different life histories of many vertebrate and invertebrate species, and the habitat differences between caves and the much more extensive, but less studied underground matrix outside caves. However, a useful starting point for understanding the general characteristics of subterranean species is provided by various schemes that categorise species according to their dependence on the underground environment. These schemes are discussed in detail by Sket (2008), but, in summary, species occurring only in the aphotic zone of caves or deep underground are classified as troglobites or stygobites (Table 1). The terms troglophiles and stygophiles are applied to species found in parts of caves where there is some penetration of light or to species that use surface habitats for one (usually short) part of their life history. Occasionally, troglophilic or stygophilic species may have some surface populations and some wholly subterranean populations. The third category, trogloxenes and stygoxenes, is applied to primarily surface species that regularly make use of caves or underground habitats, often as a refugium during periods of adverse conditions (such as drought) in their usual surface habitat.
Published Version
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