CONSERVATIONOF CAVE FAUNA: MORE THAN JUST BATS
David P. Slaney and Philip Weinstein
DepartmentofZoology,JamesCook University, Townsvillc. Old 4811, Australia
Abstract
Slaney, D.P. andWeinstein, P., 1997. Conservation ofcave fauna: more thanjust bats.
Memoirs ofthe MuseumofVictoria 56(2): 591-596.
Theexpansion ofbiospeleology as a scienceandcavingasarecreationalactivityhaveled to acorrespondingincreasein pressureoncavesandtheirecosystems.Thethreats include direct humandisturbance fromvisitation,andindirect modificationstocave habitatsand the surrounding environment. Despite the high profileof conservation issuessuch asthe threat topopulationsof ghostbats,littleworkhasbeencarriedoutinAustraliatoassessthe impactofhumansoncaveecology.The aimofthisstudywastobrieflyreviewtheeffectsof disturbance on populations of cave invertebrates, and to investigate the impact that sampling may haveupon them.
Werecordedtheweeklytotal of individualsof each macroiitvertebrate species collected overonemonth ofcontinuoustrapping with a variety ofmethods in Rope LadderCave, FanningRiver Caves. North Queensland.Theresultsindicatedthat numbersof pseudos- corpions, cockroaches, rhizophagid beetles, and pselaphid beetles declined significantly overthesamplingperiod.Samplingofcaveinvertebratesfor scientificpurposesmaythere-
forehave an impact on the population dynamics ofcave species, and may consequently affectthe ecology of thecaveitself.Werecommendthatthe general ecology oforganismsin a cave beinvestigated beforeany intensivesamplingiscarriedout,andthatwherepossible, samplingwith replacement should be used.
Introduction
Caveenvironmentsareuniquehabitatsthatare sufferingfrom increasing pressuresplaced upon them. Caves contain a wide range of invert- ebratetaxa,suchascrickets,cockroaches,milli- pedes, amphipods, isopods, and arachnids.
Many ofthese organisms show morphological modifications (troglomorphies) that are not found in corresponding surface dwelling (epigean) species. Troglomorphies include reduction or loss of eyes, wings, and bodily pigmentation, and attenuation of appendages (Barr, 1968; Culver, 1982, Kane and Richardson, 1985). Many ofthese species are relicts, having few orno closelyrelated epigean species.Althoughalargeamountofresearchhas been carriedoutonAustralia'stemperate caves (Hamilton-Smith, 1967, 1987; Richards, 1971;
Eberhard, 1993; Eberhard el al., 1991), few studies have looked at our tropical caves. Not
until the early 1980s did entomological studies delve deeperintoNorth Queenslandcaves.This workled to the discovery ofa rich and diverse range oftropicalcave fauna includingsandflies, plant hoppers, assassin bugs, and cockroaches (Lewis and Dyce, 1983; Hoch and Howarth, 1989a. b, Malipatil and Howarth, 1990; Roth,
1990).OneexpeditionbyHowarthandStonein
1985 recorded over 40 species of cave arthro-
podsfrom Bayliss lavatubeat Undara,sevenof whichwere newspecies(tworepresentnewgen- era)and24 ofwhichweretroglobites(Howarth and Stone, 1990). We have discovered further
new species, including a pseudoscorpion, and several sibling species of cave cockroaches (Weinstein and Slaney, 1995). Caves are not only importantwith respecttodocumenting and preserving biodiversity, but are important for studying adaptation, speciation, and species
interactions. They provide us with natural lab- oratories in which wecan frame andtest evol- utionary hypotheses.
Caveorganismsare particularly vulnerableto disturbanceastheylivewithindiscretehabitats, with isolated island like distributions. Species are particularly vulnerable when endemic species areconfinedtooneortwocaves withina karstregion. Forexample, nearChillagoe, Qld, four smalllimestone towers occur withina 2km-
areawithinwhichseveralendemiccave adapted arthropods are found, with some being restric- tedto singletowers(Hoch and Howarth, 1989b).
Populationsizesare often small,and dueto their isolateddistributionmay exhibit a limitedgene pool and restricted geneflow, which may result in severe bottle necks, further increasing their vulnerability (Barr and Holsinger, 1985;
Caccone, 1985; Culver, 1986). Thesmall sizeof
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https://doi.org/10.24199/j.mmv.1997.56.55
caves, compared to surface habitats, also reduces the resilience of such species to disturbance.Disturbancesmaynotonlyresult in the extinction of these organisms, but in the destruction of the unique cave habitat itself.
Disturbances can be categorised as either indirect(broughtaboutby modificationstocave habitats and the surrounding environment) or direct (brought about by human visitation to caves).
Indirectdisturbance Deforestation
Clearing ofvegetationfortimber,mining,and roadconstructionchanges local hydrology, and causes severe erosion and increased frequency and intensity of flooding (Lichon. 1993). In
NSW and Victoria approximately 60% ofthe karst regions have had their native vegetation
removed or severely modified (Eberhard and Spate, 1995), while in Tasmania, most caving areas are covered by intact temperate forest
which is underthreatbyclearingforthewood- chipping industry (Lichon, 1993). Populations of glow worms in Flowery Gully caves, Tas- mania, were wiped out as a result of clearing vegetation,anactwhichmadeaoncepermanent subterranean stream become intermittent, in turn lowing the high humidity in the caves required by the glow worms (Lichon, 1993).
Clearing ofvegetation near cavesalsoremoves themajorsourceofnutrient input,dramatically lowering the food available to cave invertebrates.
The exposure of soils surrounding caves caused by clear felling, quarrying, and farming increases the rate oferosion, resulting in high levelsofsediment depositionincaves (Kiernan, 1988). High levels of erosion at an Ida Bay quarry, in Tasmania, has caused clay to be washed into surrounding caves(Lichon, 1992).
Thedepositionofclayincavepassagesnormally containinggravel substrateshasledtothelossof cave invertebrates adapted to living in such habitats (Eberhard, 1995). Scouring of organ- isms from their stream habitat can also occur during periods of flooding (Chutter, 1969), while at Mole Creek Caves, Tasmania, land clearing has resulted in rapid subsidence and collapseof cave systems(Lichon, 1993).
Changingwaterlevels
Flooding induced byland clearance orbythe constructionofdamscan obliterate entirecave communities. Cave communities at Texas in Queensland, BurrinjuckinNSW, Dartmouthin VictoriaandLorinnainTasmania haveallbeen
lostas a resultofdam constructions(Eberhard and Spate, 1995). Alternatively, lowering the water table can have a similar effect on cave invertebrates. In Yanchep, Western Australia, groundwater pumping is threatening aquatic cavespecies (Jasinska and Knott, 1991). In the Naracoortecaves, SouthAustralia, the transpi- ration from overlying pine plantations has reduced the amount ofwater seeping into the caves, resultingin cave desiccation.
Quarrying
Inaddition tochanginglocalflowregimesand increasing sedimentation rates, quarrying of limestone for cement and other building materials(egmarble)oftenentailsthecomplete destructionofacaveandevenentire karsttower systems. Blastinginthevicinityofcaves canalso causeseverestructuraldamagetothem,altering the microclimate within. Limestoneoperations
atMountEtna,Queensland, haveledtonumer- ous caves being destroyed, including ghost bat (Macrodermagigas) maternity caves (Eberhard and Spate, 1995), and presumablytheir associ- ated invertebratecavecommunities.
Pollution
Caves are often used fordumpingofagricul- tural, industrial and public waste. The occur- rence ofsudden large influxes ofnutrients (eg
deadfarm animals) canlead to the introduction ofsurface invertebrates and allow some cave species to out-compete others, upsetting the delicate ecological balance (Chapman, 1993).
From 1900to 1976 wasteandwashwaterfroma cheese factory and abattoir in Yahl, Mount Gambier, SouthAustralia, was discharged into an unconfined limestone aquifer. The effluent
contaminated groundwater, resulting in abnormally high nitrate levels in the surround- inglimestone karst(Slaney and Ragusa, 1990).
At MoleCreek,Tasmania, stock accesstokarst regions and dairy effluent runoff"has increased nutrient levels, resultingin highbacterialpopu-
lations incave waters (Lichon, 1993). Pesticides and fertilisers may also be washed into caves from surroundingagricultural land (Chapman, 1993, Lichon, 1993). Cave entrances may not only be blocked by waste but infilled to make way for farming, roads and housing develop- ments. Suchblockages lead toadecrease in the
amount ofnutrient input into the cave ecosys- tem and result inthe depletionorextinctionof cave invertebrates (Culver, 1986).
Tourism
Constructionof pathsandwalkways,lighting, gates on cave entrances, and widening ofcave
entrancesfortourism,create a numberof prob- lems for cave organisms (e.g., Webb, 1984).
These constructions lead to the alteration and
loss of habitat, upon which highly adapted organisms depend, by altering cave tempera-
tures,humidities andatmospheric composition
(e.g., Pugsley, 1984). Artificial lightingused for tourism can enable the establishment ofplants that would not beable tosurvive inthenormal conditions of little to no light. In turn, intro-
duced plants may provide habitat for surface dwelling invertebrates, thus altering cave com- munity composition (Howarth, 1982; Eberhard andSpate, 1995).Construction ofgateswithlow
sills have a tendency to trap leaf litter which would otherwise be washed into caves, as has occurredattheentrancetoKublaKhanCavein
Tasmania (Spate and Hamilton-Smith, 1991).
Changes to cave microclimates also affect bat maternity sites and associated cave invert- ebrates(Tuttle, 1979).Theplacementofair tight doors to control desiccation of speleothems in AlexandraCaveatNaracoorte,South Australia, has wiped out populations of rhaphidophorid cave crickets (Hamilton-Smith, 1987).
Direct disturbance
Damagetocavesand thelossof cave faunamay
becauseddirectlybyhumanvisitation.Visitsby the generalpublic,cavingclubs,andresearchers result in the trampling of some cave invert- ebrates (Spate andHamilton-Smith, 1991),and the compaction of cave floor sediments occu- pied by others (e.g., crickets and beetles.
Middleton, 1979). At Mount Widderin Cave.
Skipton, Victoria, an invertebrate community
living on unconsolidated substrate has disappeared as a result of soil compaction by high numbers of human visitors (Spate and Hamilton-Smith, 1991).Inadditiontosoilcom-
paction, walking through cave pools may
adversely affect aquatic invertebrates. In Tas- mania, rare psammaspid and syncarid crus- taceansareconfinedtosuchhabitats(Eberhard, 1993), and alterations of turbidity in their waters may critically alter their environment.
Cavevisitors also posea potential threat tocave invertebratesbyintroducingorganisms fromthe surface and from other caves which may out- compete and displace the extant cave fauna.
Cavevisitation mayalsoresult in thetrampling
ofplant roots,leadingto thelossofroot feeding invertebrates and their predators (Howarth, 1982).Cavevisitorsusing acetylene torchesmay
alsoimpactoncaveorganismsthroughthe toxic calcium carbide by-product ofthese torches.
Generally,cavesas discreteconfined habitats tend to have a carrying capacity of visitation,
above which level of disturbance collapse of cave communities is likely to occur (Howarth and Stone, 1982, Spate and Hamilton-Smith, 1991). Fielddataon cave faunadistributionsin
Hawaiian lava tubes by Howarth and Stone (1982) show that species diversity and popu- lation levels are inversely proportional to the level ofvisitation and human disturbance. Dis- turbance of bat colonies brought about by
human visitation, (particularly by bat researchers !) has contributed to the declineof
many colonies (Tuttle, 1979). Bat decline from humandisturbance hasbeenobservedincentral and south-eastern NSWcaves (Hall and Duns- more, 1974). In turn, the lossofbats hasled to the lossofendemic guanophilic invertebrates.
Impact ofscientificstudies
Despitethe highprofileof conservationissues such as the threat topopulations of ghost bats, little work has been carriedout in Australia to assess the impact ofhumans on cave ecology, with no studies on the effect that trappingmay have on cave invertebrate populations. Key
(1978)and Heath(1987) claimedthat thereisno evidence of collecting ever affecting a popu-
lationofinsects detrimentally.However,declin- ingpopulations ofthe collectedBathurstCopper
Butterfly suggest otherwise (Dexterand Kitch- ing, 1993), and we provide evidence in this paper that intensive sampling of cave invert- ebrates can deplete populations. Culver(1986) stated thatworldwide,oneofthedangerstocave fauna isthe appallingnumberofspecies threat- ened by over-collecting for scientific purposes, but he citesfew data tosupport thisstatement.
With this inmind weanalysedpast datawehad obtained in investigations of tropical cave fauna, to assess the impact that our sampling may have had on populations of cave invert- ebrates.
During August 1993 we surveyed the macroinvertebrate fauna ofRope LadderCave, FanningRiver Caves,intropicalnorth Qld.and recorded theweekly totalofindividualsofeach macroinvertebrate species collected over one monthof continuous trapping with four differ- ent methods concurrently (pitfall only, baited pitfall, leaflitterdry, andleaflitterwet,withno replacement; WeinsteinandSlaney, 1995).Four species were trapped in sufficient numbers to look for trends in their frequency of capture.
Pseudoscorpions, cockroaches, rhizophagid beetles, and pselaphid beetles showed a signifi- cant declineinnumberoverthesampling period (from 12, 44. 680 and 18 individuals to 5, 25, 250 and 4individualsrespectively). Giventhat sampling occurred at thesame time ofdayand that wefound noseasonal effects(e.g.,periodic rainfall)impactingonthesepopulations during the study period (Weinstein, 1994; Weinstein andSlaney. 1995), the probabilityof recordinga simultaneous decrease in populations of four different species by chance alone is 0.0625 (0.54). Thus,the datasuggest thatour sampling of cave invertebrates adversely affected their numbers.
Past studieshavealsoindicated thatsampling
may have adverse effects on cave populations, withpitfall trappingreducingcavebeetlepopu- lations (Peck, 1975, 1976). All that may be required to extinguish the local population ofa cave dwellingspeciesisthecarelessor accidental desertion of a pitfall trap (Vandel, 1965;
Howarth,1982).Asingletrapinarestrictedarea
may not only trap a species to extinction, but
may subsequentlyaffect theecology ofthecave
itselfthroughchangesinthepopulationdynam-
icsofthe survivingcavefauna.Apossiblewayof minimising such impacts is to sample with replacement,oriftrapsitesare tobeleftin situ foran extended period oftime, to use a 'trap'
which allowsforthe freemovement ofindivid- uals. We have designed a survey tool which meets both ofthese requirements (Slaney and Weinstein,in press).Awetleaflittertrap(which simulates nutrientinflux intodrytropicalcaves duringmonsoonal rains)maintainstheviability of organisms, thus allowing their release back into the cave environment following identifi- cation and counting. Because this trap is not only conservation friendly but is also more
effectiveand moreefficientthan other sampling techniques (Weinstein and Slaney, 1995), we recommend it as the survey tool of choice in thesefragileecosystems(SlaneyandWeinstein,
in press).
Implications
ComparedwiththeUSA,Australiaisextremely depauperate in numbers of caves (Jennings, 1983). Despite this, Australian caves are of international significance, containing a diverse range of cave organisms. Cave habitats in
Tasmania are amongst the richest temperate cave communities(Eberhardand Spate. 1995), while tropical caves in Western Australia and
Queensland havean exceptional abundance of cave species (Humphreys, 1993, Howarth,
1988). LegislativelyonlyTasmaniaand Western Australia recognises cave invertebrates as important, but even then only on a species by species basis (New. 1984; Eberhard and Spate, 1995; Humphreys, pers. comm.). The formu-
lationof conservationpolicies/strategies forpro- tectingcave invertebrates is difficult dueto the lackoftaxonomicandecologicaldata. The lack of such datais obviously not aproblem unique to caves, butisamajorshortfallwhichthreatens the conservation of Australia's invertebrate faunaonthewhole (New,ms.).Cavesmorethan most other ecosystems can play an important role inmakingboththe publicandpolicymakers aware ofthis problem, as they tend to have a relatively high local profile(e.g.,Jenolan Caves, UndaraLavaTubes, andChillagoeCaves,allof whicharerich incave faunaandprovide import- ant local landmarks).
Oneoftheproblemsfacingcaveresearchersis
determining whetherinsectspecies are rare, as they are oftendifficulttoobserveduetocamou-
flagingadaptations, the crypticmicrohabitatsin
which they live (cracks or rock piles), and the inaccessibility of the cave in the first place.
Further, individuals within each population
maybeableto findrefugesfrom whichtheycan continually recolonise other cave regions, thus demonstrating patchy distributions both in space (location) and time (seasons). Howarth (1983) stated that there is a requirement for experimental ecological studies to determine what factors limit cave species distribution, whatare thesignificant perturbations, and how
thesedisturbancesaffectcavecommunities.For example, long term ecological research is
required to establish methodologies for dis- tinguishingbetweenshort term populationfluc- tuations and longer term irreversible changes (Howarth and Ramsay, 1991).
Generally, biologists recognised that insect species are endangered to the extent that their habitats are endangered, and that theirconser- vation can be accomplished only by conserving their habitats (Key, 1978). With cave ecosys- temsthe surfaceandsubsurface drainagebasins are coupled, forming a highly integrated unit (White el al., 1995), and the conservation of cave faunawouldthusbebest achieved by pro- tectingthecave ecosystem andthesurrounding catchment area (not just around the cave entrance)fromthesortsof disturbanceswehave outlinedin thispaper(includingscientists!).We
recommendthatecosystemstabilityandvulner-
ability to disturbance, as well as the general ecology of organisms in a cave, be considered beforeanyintensivesamplingiscarried out. We
further recommend that any sampling be done with replacement using techniques similar to ourownleaflittertraps(SlaneyandWeinstein, in press). For cave communities where direct visitation is havingan effect on populations of cavespecies,accessmustberestricted,andtour- ismshouldbeestablishedonlyincaves withfew species. Where possible, caves immediately adjacent to such tourist caves should have restricted access to allow organisms to retreat into a readily available refuge.
The faunas of many caves which are under threat either directlyorindirectlyhavenotbeen investigatedatall,andmaynever be discovered withoutdetailedtaxonomic andecological stud- ies. Cavesare auniquebiologicalresource with both scientific and cultural importance, especially for invertebrates.Wemustnotneglect the biodiversityandconservation value ofthese habitats, always bearing in mind that conser- vation strategies can only be as sound as the research upon which they are based (New, ms.).
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