Troglophile

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Organisms living in caves , especially cave animals , are divided into ecological groups according to their attachment to the subterranean habitat.

  • Troglophil are populations or species that regularly live in caves, but which also occur regularly and permanently in above-ground habitats.
  • troglobiont , also synonymous troglobit (outdated also antrobiont) are populations or species that live permanently and exclusively in caves, of which no permanent aboveground occurrences are known.
  • Trogloxes are populations or species that are found in caves, but can not complete their life cycle here . These are either those that only occasionally penetrate caves (errant guests), but have their actual habitat above the earth. Other authors also use the term for those who can be found here regularly, but at least in one stage of life are necessarily dependent on leaving the cave.

This classification originally goes back to the Austrian entomologist Ignaz Rudolph Schiner (1854), modified by the Romanian biologist Emil Racoviță (mostly transcribed as Racovitza) (1907), and is therefore called the Schiner-Racovitza system . The system has often been criticized for being imprecise; numerous biological speleologists (biospeleologists) have suggested modifications or different terminology. Unfortunately, the terms defined above are sometimes used with slightly different meanings, without the researchers always disclosing which terminology they follow in each case. This must be taken into account when interpreting.

Barr system: Trogloxene redefined

The American cave explorer Thomas Calhoun Barr jr. (1968) proposed a modified Schiner-Racovitza system in which he mainly redefined the meaning of the expression trogloxen. According to Barr, sheer wanderers who actually cannot live in caves deserve no special technical term. Instead, he used the term trogloxene for those organisms that regularly live in caves that have to leave them at some point, for example to look for food outside. Trogloxene in Barr's sense are many of the classic cave animals such as cave bats, fat swallows or the extinct cave bears and other species of the Ice Age megafauna. Barr's proposal has been taken up in many international countries, but has not prevailed in the German-speaking area.

However, this use of the term is not applied uniformly either. For example, some authors also use the term troglophiles for species that actually live underground, but have to leave the cave at a certain stage in their life.

Christiansen system: Troglomorphs

In 1962, the American entomologist Kenneth A. Christiansen proposed a new system in which organisms should not be classified according to their habitat but according to morphological adaptations . After that, troglomorphic organisms are named that show special adaptations to the subterranean habitat . On the one hand, there are positive adaptations (progressive evolution), such as enlarged or lengthened tactile organs or body appendages, as well as loss mutations (regressive evolution) of organs that are no longer needed, such as non-functional or completely regressed eyes. Some researchers have criticized that the term "troglomorph" (translated cave-shaped) is linguistically inappropriate and instead use the term "troglobiomorph" in the same sense. Christiansen's term troglomorph is used by many authors to characterize organisms that would be called troglobiont / troglobit in the classical system. The parallel coined terms “ambimorph” for organisms that show only a few adaptations to the subterranean habitat, and “epigiomorph” for organisms adapted to above-ground life, however, have not caught on and are no longer used.

However, not all species that are strictly bound to caves (troglobionts) also show corresponding morphological adaptations (troglomorphs). So the terms are not congruent.

Classification of aquatic organisms: stygobionte

The Schiner-Racovitza system is used by many biospelaeologists for both air-living and air-breathing as well as aquatic organisms. In limnology , however, a second system has established itself, which originally goes back to the zoologist and limnologist August Thienemann , but which was only popularized in its international use through the work of Janine Gibert. Accordingly, the water-living, occurring below the surface species or troglofauna divided into stygobionte (synonym stygobite ) stygophile and stygoxene whose definition substantially equal to that of the classical system corresponds. This terminology is used by some limnologists for aquatic organisms instead of the Schiner-Racovitza system. Others reserve them for the habitat of the groundwater and continue to use the classic system for actual cave animals.

System according to Pavan and Ruffo: subtroglophiles

The Italian researchers Mario Pavan (1944) and Sandro Ruffo (1957) used the classic Schiner-Racovitza system, but were bothered by the category of troglophiles, which in their opinion was vague and imprecise. They introduced the new term subtroglophiles for organisms that regularly live in caves, but have to leave the cave habitat at least in one stage of life (for example for nutrition or reproduction) . The “real” troglophiles, i.e. those who can complete their entire life cycle inside caves, but of which there are also populations living purely above ground (in the same area of ​​distribution), are now called eutroglophiles . This nomenclature is recommended, for example, in an influential work by Boris Sket and is widely used; other researchers, on the other hand, regard it as a superfluous, tendentially confusing addition and recommend instead using the term trogloxene in the modified definition according to Barr.

Troglodyte

The term troglodyte ( caveman ) is used for human inhabitants of caves, especially the (sub) fossil remains of these. The term derived from ancient Greek ( ancient Greek τρωγλοδύτης trōglodýtēs , German 'who slips in caves, lives in caves, in particular the name of a bird [similar to our wren]' ) is already attested in antiquity (for example in Herodotus ). Carl von Linné was mistakenly convinced of the existence of a cave-dwelling night owl " Homo troglodytes ", later the term was used for the bones of the Neanderthal man , which were often found in caves . So although the term is much older, it was never used to refer to cave-dwelling species.

Delimitation of the cave habitat

For the classification of cave dwellers it is of great importance in which definition the basic term “cave” is used. For cave researchers (speleologists) an underground cavity is usually only considered a cave if it is large enough to allow people to enter. Numerous biospeleologists have repeatedly pointed out that this definition is meaningless for the mostly much smaller, cave animals. Usually colonists of smaller underground cavities are also considered troglophilic if they otherwise meet the relevant criteria, at least if the colonized cavity is large in relation to the body size of the animal. However, this results in problems of delimitation to the soil fauna and the groundwater fauna . Some biospelaeologists point to the special importance of small, near-surface crevice systems, especially in karstified limestone , known as epicarsts, which have an independent fauna that is clearly different from the actual soil fauna. The colonists of these "superficial subterranean habitats" (SSH) are mostly counted among the cave fauna, with which they have a lot in common, and are therefore considered troglophilic. However, not all researchers follow this usage. There are now indications that the "superficial subterranean habitats" could be an independent habitat with its own fauna.

Real caves are characterized by the absence of light, called aphotic . However, there is a wide transition zone in the area of ​​the cave entrance, which, depending on the conditions, extends more or less far into the interior of the cave.

Troglobionts, i.e. species specially adapted to cave life that have no aboveground occurrence, are often difficult to detect in practice, since not all habitats are equally well investigated and it is, by definition, impossible to prove the absence in a habitat (is only possible , so far unsuccessful to look for presence). It is also difficult to explain how it is possible that certain types of cave colonize widely spaced, underground cave systems that are clearly not interconnected. Eleonora Trajano and Marcelo R. de Carvalho therefore propose that all definitions according to the Schiner-Racovitza system should be strictly related to the population. In their opinion, the occasional occurrence of individuals in the “wrong” habitat should play just as little a role as the requirement for morphological adaptations. Such would often occur in troglophiles in the same way as in troglobiont species.

Individual evidence

  1. ^ Claude Boutin: Organisms: Classification. In John Gunn (editor): Encyclopedia of Caves and Karst Science. Fitzroy Dearborn (Taylor & Francis), New York 2004. ISBN 0-203-48385-5 , pp. 1170-1175.
  2. ^ Hubert Trimmel (Red.): Speleological specialist dictionary. Files of the Fourth International Congress for Speleology, Vienna - Obertraun - Salzburg 1965, Volume C. published by the Regional Association for Speleology in Vienna and Lower Austria, Vienna 1965.
  3. ↑ a b Boris Sket (2008): Can we agree on an ecological classification of subterranean animals? Journal of Natural History 42 (21-22): 1549-1563.
  4. ^ Eleonora Trajano: Ecological Classification of subterranean Organisms. in David C. Culver, William B. White (editors): Encyclopedia of Caves. Elsevier / Academic Press, Amsterdam etc., 2nd edition, 2012. ISBN 978-0-12-383832-2 . Pp. 275-278.
  5. ↑ Thomas C. Barr Jr. (1968): Cave Ecology and the Evolution of Troglobites. in Theodosius Dobzhansky, Max K. Hecht, William C. Steere (editors): Evolutionary Biology, Volume 2. Springer-Verlag, Boston 1968. ISBN 978-1-4684-8096-2 , pp. 35-102.
  6. ↑ Stefano Mammola & Marco Isaia (2017): Spiders in caves. Proceedings of the Royal Society B 284: 20170193. doi: 10.1098 / rspb.2017.0193
  7. ↑ Kenneth Christiansen: Morphological Adaptations. in David C. Culver, William B. White (editors): Encyclopedia of Caves. Elsevier / Academic Press, Amsterdam etc. 2005. ISBN 0-12-198651-9 , pp. 386-397.
  8. ↑ a b c Eleonora Trajano & Marcelo R. de Carvalho (2017): Towards a biologically meaningful classification of subterranean organisms: a critical analysis of the Schiner-Racovitza system from a historical perspective, difficulties of its application and implications for conservation. Subterranean Biology 22: 1-26. doi: 10.3897 / subtbiol.22.9759
  9. ↑ Jürgen Pust (1990): Investigations into the systematics, morphology and ecology of the aquatic cave animals found in Westphalian caves. Treatises from the Westphalian Museum of Natural History 52 (4): 1–188.
  10. ^ Erhard Christian: Cave animals. In C. Spötl, L. Plan, E. Christian (editor): Caves and Karst in Austria. published by the Upper Austrian State Museum, 2016., pp. 233-254.
  11. ^ Wilhelm Pape , Max Sengebusch (arrangement): Concise dictionary of the Greek language . 3rd edition, 6th impression. Vieweg & Sohn, Braunschweig 1914 ( zeno.org [accessed October 31, 2019]).
  12. ↑ Ralph Crane, Lisa Fletcher: Cave: Nature and Culture. Reaction Books, London 2015. ISBN 978-1-78023-431-1 .
  13. ↑ David C. Culver and Tanja Pipan (2008): Superficial subterranean habitats - gateway to the subterranean realm? Cave and Karst Science 35 (1/2): 5-12.
  14. ^ Tone Novak, Matjaž Perc, Saška Lipovšek, Franc Janžekovič (2012): Duality of terrestrial subterranean fauna. International Journal of Speleology 41 (2): 181-188. doi: 10.5038 / 1827-806X.41.2.5
  15. ^ David C. Culver and Tanja Pipan: Insects in Caves. Chapter 6 in Robert G. Foottit and Peter H. Adler (editors): Insect Biodiversity: Science and Society, Volume II. Wiley / Blackwell, 2018. ISBN 978-1-118-94557-5 .
  16. ↑ Luis M. Mejía-Ortíz, Tanja Pipan, David C. Culver, Peter Sprouse (2018): The blurred line between photic and aphotic environments: a large Mexican cave with almost no dark zone. International Journal of Speleology 47 (1): 69-80. doi: 10.5038 / 1827-806X.47.1.2155