Reprintedfrom: ECOSYSTEMSOF THE WORLD 30 SUBTERRANEANECOSYSTEMS Editedby Prof. Dr. Horst Wilkens Zoologisches Institut und Zoologisches Museum der UniuersitcitHamburg, M artin-Luther- Kin g-P latz 3, 20146 Hamburg, Germany Prof. David C. Culver The American UniuersiQ, 4400 MassachusettsAuenue, Washington,DC 200I 6-8002, USA Dr. William F. Humphreys WesternAustralian Mus eum, Francis Street, Perth, WesternAustralia 6000, Australia 2000 ELSEVIER Amsterdam- Lausanne- New York- Oxford - Shannon- Singapore- Tokyo Chapter0 BACKGROUNDAND GLOSSARY W.F.HUMPHREYS INTRODUCTION within biospeleology,and the issuewill not be pursued here at length. As with other specialized subjects, a plethora of Trogiobiteswere long consideredto be phylogenetic terminology and definitions has come to surround, or distributional relicts driven into caves by climatic sometimesto obscure,the discipline of biospeleology change,especiaily in the Pleistocenerefugium model. (speleobiology,stygobiology, . .), terms sometimesso Recently, cave colonization has been viewed as an subtly different - even synonymous as to confound active process - the invasion of a vacant habitat. even researcherswithin the discipline (for a fuller Notwithstanding,the undergroundrealm does harbour treatmentsee, for instance,Camacho, 1992). many distributionaland phyletic relicts. The terminology coverssix main themes: Anchialine waters (inland groundwaterwith current ( I ) How a speciescame to be underground. marine connections)harbour a distinct (Sket, 1996) (2) The degree of dependenceof a specieson the and, in some areas! a predictable fauna (Yager and undergroundrealm. Humphreys,1996). (3) Whether a speciesshows adaptations to the under- Stygofaunawith marine ancestryare consideredto ground realm. colonize the shore line and to becomeisolated inland (4) Whether a species inhabits subterraneanvoids by marine regressionfollowing a period of manne filled r,vithwater or with air, and which part(s) of transgression(Stock, 1977; Boutin and Coineau,1990; each it inhabits. Notenboom,l99l ; Holsinger,1994). (5) The delimitation of the various hypogean sub- systems. The degreeof dependenceof a specieson the (6) The amountand origin of the energysource for the underground realm ecosyslem. As a backgroundto this volume,the main themesre- Organisms have many pathways of interaction with curring in biospeleologyare introduced below, followed subterraneanspaces (Gibert et al., 1994); some are by a Glossary. only found underground,while others move in and The subjectof cavesis well introducedby Gillieson out ol the hypogean realm. More than twenty spe- cial nomenclature schemes have proposed (1991), while the literature pertaining to karst hy- been to describethese relationships,based on morphological, drology, encountered especially in the context of behavioural,and ecological adaptationsof animals to stygofauna,is accessiblein Fordand Williams (1989). undergroundlife and on their presenceor absencein caves(troglofauna; see review in Camacho,1992). How a speciescame to be underground ln the Schiner-Racovitd system (Schiner, 1854; Racovitza,1907), cave-inhabiting animals are grouped This issueis coveredfrom dilferent stancesin several by their degreeofdependence on the caveenvironment: contributions to this volume (e.g. Chapter 21 by troglobitesare specieswhich do not existoutside caves; Holsinger,Chapter 22 by Humphreys,and Chapter3l troglophiles may live and reproduce underground as by Deharvengand Bedos) as the topic is all-pervasrve well as in the epigean domain; whlle n'ogloxenesdo 4 W.F.HUMPHREYS not normally feed underground, but may enter caves which togetherproduce the convergence,characteristic actively (regular trogloxene) or passively (acciden- of cave-adaptedanimals, that is termed troglomorphy. tal trogloxene).Additional criteria have subsequently These adaptations include morphological, ecologi- entered these purely ecological definitions, so that cal, physiologicaland behaviouralcharacteristics (Ta- they have become a variable mix of biological and ble0.1). morphologicalcriteria (Howarth, 1973:p. 142). The lack of detailed ecological information for Whether a speciesshows adaptations to the most cave-inhabitingspecies leads to ambiguity, and underground realm this is to some extent overcome by the concept of troglomorphy (Christiansen,1962), which permits Organisms have many pathways of interaction with classificationof the cave inhabitantsusing a iess am- the subterraneanrealm. While some are only found biguous morphologicaldefinition (troglomorphic/non- underground,others move in and out of the hypogean troglomorphic species)rather than the ecologicalone environmentas indicatedin the ecologicalclassification (troglobitic/troglophilic/trogloxenicspecies); but this of speciesby the terms troglo(stygo)bitic,troglophilic term is itself being infiltrated by behavioural and and trogloxenic. physiologicalattributes (Tabie 0.1). It is important to note that functionally these categoriesare more diffuse than is suggestedby their Table 0.1 ecological context. For example,while stygo(troglo)- Characteristicsof cave organismsrelative to surface organlsms xenesmay occur undergroundonly accidentally,they troglomorphies I may influencehappenings in the hypogeanrealm, for example,functioning either as predatorsor prey (e.g. Morphological Gibert et al. 1994: p. l1), as well as constituting Specializationof sensoryorgans (chemo-, hygro- thermo- and a subset of the allochthonousinputs from epigean baro-receptors) sources. Elongationo1' appendages In consideringtroglomorphic correlates (e.g. reduced Reductionof eyes,pigments and rvings eyes,pigment, wings etc.) it is necessaryto distinguish Cuticle thinning (in terrestrralarthropods) whether the traits are different from close epigean (in Foot modification Collernbolaand planthoppers) ancestors(apomorphic) or simply characteristicsof the Scalereduction (in fish) group or lineage(.plesiomorphic). E co I ogic al and l:ehoo io tu'uI Slowing metabolisms Whether a speciesinhabits subterranean voids Starvationresistance filled with water or with air, and which part(s) of each it inhabits Relaxctionand degencratronof circadranrhyhrns I n*,^.o.4 fe,",-.lit., While the Schiner Racovitrdsystem is often used for lncreasedegg volume both terrestrialand aquaticspecies! Gibert et al. (1994: Increasedlife span p. 13) have proposed stygo- (.sensulato) as the most Behauioural ecologicallydescriptive prefix for groundwaterfauna. Decreasedaggregation (in Collembola) Hence, troglofauna becomes restricted to terrestrial Reducedreaction to alarm substances(in fish) systems (see review in Camacho, 1992), while the Increasedsensitivity to vibratlon aquatic fauna is referred to generally as stvgofauna (Ginet Reducedintraspecific aggre:sion and Decou, 1977; Botosaneanu,1986; Gibert et al., 1994).There are complex parallel classifications I From Culver et al. (1995), after Chdstiansen(1992). in use for aquatic subterraneanorganisms (e.g. Boto- saneanu,1986: endpaper; Williams, 1984;Stanford and Many species found living underground display Ward, 1993). certain characteristictraits that are thought to be Gibert et al. (1994) followed the main Schiner adaptiveto undergroundlife. These include both the Racovitrdsystem, replacing the prefix "troglo-" by reduction or loss of characters(regressive evolution) "stygo-" (hence,stygoxene, stygophile, stygobite). ln and the enhancementof others(constructive evolution), porous aquifers,stygophiles are subdividedinto three BACKGROUNDAND GLOSSARY 5 categories:occasional hl,porheos, which comprises in some tropical areas(Cape Range, Australia), highly essentiallythe larvae, especially of aquatic insects, troglomorphic (and stygomorphic)species are found, of most of the benthos;amphibites, whose life cycle under certain conditions,to be leeding in sunlight at requires the use of both surface and groundwater the entrance to caves. However, even within caves, systems;and permanent hyporheos,which comprises the boundariesbetween zones are dynamic, shifting, a diverse assemblageof organismspresent in all life inter alia, accordingto the degreeof biogenic carbon stagesin the groundwateror in the benthic habitats dioxide production(dependent on periodicity of water an aerial epigeanstage is not requiredto completethe and energy inputs), the weather, the season and life cycle. major climatic events. The extent of the zones and Stygobitesare subdividedinto two classesofobliga- their vagility varies between caves according to the tory hypogeanforms: ubiqtdtousstygobites are widely relative sizes of entrancesand volume, and the size, presentin both karstic and alluvial groundwatersand shapeand arrangementof the chambers(see Racovita, are sometimes found very close to the surface. ln Chapter28, this volume). contrast,phreatobite species are stygobites that are restrictedto the deepgroundwater substrata of alluvial aquifers(Gibert et al., 1994). The amount and origin of the energy source for the ecosystem Delimitation of the various hypogean sub-systems In the absenceof light subterraneanecosystems have The hypogeanrealm used to be defined in terms of been consideredto be dependenton organic matter cavesand the degreeof darkness.The realizationthat fixed by photosynthesis and reaching the hypogean most caves had no openings to the surface (Curl, realms by various direct and indirect pathways. Routes 1966), and that troglobitic animals may inhabit the of entry are as diverseas logs being washedinto open immediatesubsurface spaces even in non-karsticareas