Table Of Content©EntomologicaFennica.13June2008
Manipulated structural variability affects the habitat choice
of two ground-living beetle species in a laboratory experiment
KarolinaNittérus,ÅsaGunnarsson&BengtGunnarsson
Nittérus, K., Gunnarsson, Å. & Gunnarsson, B. 2008: Manipulated structural
variabilityaffectsthehabitatchoiceoftwoground-livingbeetlespeciesinalabo-
ratoryexperiment.—Entomol.Fennica19:122–128.
The habitat choice of two ground-living carabid beetle species (Pterostichus
oblongopunctatus(Fabricius)andCarabushortensisLinneaus)wasinvestigated
inalaboratoryexperiment.Beetleswerereleasedintestarenaswithtwooptions
ofmanipulatedstructuralvariabilityontheground,i.e.;baregroundspotsversus
spotswithloggingresidue(slash).Beetleswerestudiedfor600secondsandthe
total time spent on bare ground versus in slash was measured. The results re-
vealedapreferenceforslashcoveredgroundamongsttheinvestigatedbeetles.
Regardlessofspeciesortypeofreleasespot(inthemiddleofthebaregroundor
inslash),thecarabidsresidedsignificantlylongerinslashcomparedwiththebare
ground. The results support recent studies emphasizing the importance of
microhabitatvariabilityfortheabundancedistributionofarthropodsinmanaged
systems.
K.Nittérus&B.Gunnarsson,DepartmentofPlantandEnvironmentalSciences,
GöteborgUniversity,Box461,SE-40530Göteborg,Sweden;correspondingau-
thor’se-mail:[email protected]
Å.Gunnarsson,Raketgatan3,SE-41320Göteborg,Sweden
Received26July2006,accepted26October2007
1.Introduction ismmayalteritsfitness(Travis&Dytham1999).
Forinstance,thesmallscaledailymovementsor
The quality of a certain habitat is mainly deter- habitatchoicesofarthropodshavemanypossible
minedbythelargescaleheterogeneityinthecho- explanationssuchasfoodsearchandprotection
senlandscapebutalsothevariabilityofthestruc- frompredation(Harwood etal. 2001, Ferguson
turalcomplexityonthemicroscale.Habitatcom- 2004), or balancing out environmental factors
plexityisregardedakeycomponentformostar- likeheatordraught(Thiele1977).Otherreasons
thropodcommunities(Thomas&Marshall1999, for specific distributions patterns of arthropods
Lassauetal. 2005). Structuralvariability ofthe maybeduetohabitatfragmentation(Schtickzelle
microhabitatfunctionsbothasadrivingforcefor & Baguette 2003) or the spatial arrangement of
arthropod dispersal (Crist et al. 1992, Martin local landscape elements (Thomas et al. 1998,
etal.2001,Buddle&Rypstra2003)andsustains Jopp&Reuter2005).
arthropoddiversity(Gardneretal.1995,Benton There are some experimental studies which
etal.2003,Boultonetal.2005). havestudiedtherelationshipbetweenarthropod
By moving in or out of different habitat habitat choice and small scale structural com-
patchesinaheterogeneouslandscape,anorgan- plexity in specific. For instance, Crist et al.
ENTOMOL.FENNICAVol.19 (cid:127) Habitatchoiceoftwocarabids 123
Table1.Thebiology,bodysizeandmainhabitatchoiceofthecarabidspeciesPterostichusoblongopunctatus
andCarabushortensis.
Biology:substraterequirements1 Rangeofbody Habitat
size(mm)1 choice2
P.oblongopunctatus inforestlitter,mossorunderpebbles 9.5–12.6 Forest
ortreestumps,onmoistground
inmixed-ordeciduousforest
C.hortensis mixedforestwiththickhumuslayers, 22–28 Forest
partlyshadedpatches,preferably
sandyground
1accordingto(Lindroth1985,1986).
2accordingtoH.Ljungberg,pers.comm.
(1992),Johnsonetal.(1992)andMcIntyreand Theaimofthepresentstudyistoexplorethe
Wiens,(1999)showedthatthemovingbehaviour mechanismsforcarabidhabitatchoice,onthemi-
ofTenebrionidbeetles(Elodesspp.)wasmainly cro scale under more controlled circumstances.
regulated by various habitat characteristics. Thestudyisthereforecarriedoutintwotestare-
Kindvall et al. (2000) found comparable strong nasinthelaboratorybyusingfield-collectedbee-
interactionsbetweensubstratevariabilityandthe tles. Carabid beetles (Coleoptera: Carabidae)
moving behaviour of Pine weevils (Hylobius were chosen as study objects, since carabids in
abietis). generalarecommon,widespread,andinhabitor
InGunnarssonetal.(2004),weshowedthat huntforpreyonthegroundofmostforestedeco-
certain forestry activities i.e., harvest of slash systems (Thiele 1977, Larsen et al. 2003). The
(logging residues from clear-cuttings) for bio- two selected species Pterostichusoblongopunc-
fuelincommercialmixedandconiferousforests, tatus(Fabricius)andCarabushortensisLinneaus
causedchangesofthegroundlayercomplexity, aretypicalforestspecies,frequentinclear-cutsall
withimportanteffectsonground-beetlepopula- over Sweden and both species have been col-
tions.Wefoundasignificantpositiverelationship lectedinourpreviousstudies.Themainstudyhy-
between microhabitat complexity (i.e. above- pothesisisthatthetwocarabidspecieswillspend
ground height of slash heaps) and beetle abun- moretimeinhighcomplexitypatches(slashcov-
dance. Moreover, species richness of morpho ered spots) than in the low complexity patches
species (i.e., beetle specimens were separated (baregroundspots)asfoundinourpreviousex-
intorecognizabletaxonomicunits(RTUs)fores- perimentsinthefield.
timatesofspeciesrichnessaccordingtoOliver&
Beattie 1993, 1996) was significantly lower in
siteswereslashwasremovedthaninsiteswhere 2.Materialandmethods
slash was left on the ground (Gunnarsson et al.
2004). Furthermore, in a follow-up experiment, 2.1.Samplingofcarabids
weinvestigatedhowcarabidsreactedtomanipu- andorganicmaterial
lations of the microhabitat complexity on the
ground of clear-cuts. We collected significantly In September 2002, 26 living specimens of the
morecarabidindividualsinthehighcomplexity two chosen carabid species, i.e., Pterostichus
patches (slash covered spots) than in the low oblongopunctatus and Carabus hortensis (for
complexity patches (bare ground spots) in the furtherinformationontheirbiologyseeTable1.)
fieldexperimentandalsowefoundasignificant werecollectedbyuseofpitfalltrapsona1-year
positive correlation between the number of oldclear-cut.Theclear-cutwaslocatedinsouth-
carabidsandtheabovegroundheightofslash,in ern Sweden, approx. 57º50’N, 12º9’E. Pitfall
non-manipulated, reference plots (Nittérus & trapswereemptiedeverythirddayandnopreser-
Gunnarsson2006). vativeswereused.
124 Nittérusetal. (cid:127) ENTOMOL.FENNICAVol.19
Alllivingspecimensofthetwoselectedspe-
cieswerebroughtbacktothelaboratoryandkept,
solitaryinmoisturizedcontainers,intherefriger-
ator (+8°C) for approximately 15days. Tosyn-
chronizethefeedingstateofthecollectedbeetles,
nofeedingwascarriedoutduringtheentireex-
periment(fromcollectioninthefieldtotheendof
the experiment). Fourteen hours before experi-
mental start-up, the beetles were removed from
therefrigeratorforacclimatizationinroomtem-
perature.Tosynchronizetheday-rhythmofbee-
tlespriortotheexperiment,eachspecimenwasil-
luminatedwithan11-Wattsfluorescenttubedur-
ing the first twelve hours, to simulate day-light
andreducenight-activebehaviour(Thiele1977,
Lindroth 1985, 1986). However, the last two
hourspriortotheexperiment,thefluorescenttube
wasshutofftostimulatetheirnight-activebehav-
iour.
The organic material, i.e. layers of moss
(Hypnum cupressiforme) and logging residue
(slash)coveringthebottomofthetwotestarenas
(describedbelow),wasgatheredonthegroundof
the same clear-cut as above a couple of weeks
prior to the experiment. To defaunate the moss
layer and slash frompossible preys prior to the
experiment,thematerialwasfirstdehydratedfor
3 weeks indoors (in room temperature) and
searchedthroughbyhand,beforebeingplacedin
thetestarenas.
2.2.Testarenas
Twocircularshapedtestarenaswereconstructed,
made out of corrugated 2-mm isolation-plastic Fig.1.Thetwoexperimentaltestarenas.TestarenaA
hasbaregroundmiddleandslashcoveredsurround-
consistingofabottomjoinedtogetherwithanen-
ings,whereastestarenaBhasslashcoveredmiddle
closure-barrier (Fig. 1). The diameter of each
andbaregroundsurroundings.
arenawas0.8mandthebarrierheightwas0.12
m.
Theorganicmaterialwithinthearenaswasar- rangements” included equal areas of bare and
rangedintwoseparateways(Fig.1);eitherwith slashcoveredgroundaswellasequalamountsof
anelongatedbaregroundspotinthemiddlesur- slashandmossonthebottomofthearenas.The
roundedbyslash(arenaA),orwithanelongated somewhat complex shape of the bare vs. slash
slash covered spot in the middle surrounded by coveredspotswasmadetoensurethattheplastic
bareground (arenaB). Thebarelayers ofmoss edge around the arena was in contact with both
(~3cmthick)withoutanyslashcoversimulated habitatsinanequalwayanddidnotaffecttheout-
“bareground”whilethe~8cmhighspotsofslash come. Consequently, although this arrangement
ontopofthe~3cmthicklayersofmosssimu- appearedrathercomplex,itsimplifiedtheexperi-
lated“slashcoveredground”.Bothtypesof“ar- ment by enabling a more straightforward inter-
ENTOMOL.FENNICAVol.19 (cid:127) Habitatchoiceoftwocarabids 125
pretation of the results. Other types of slash ar-
rangements would also have been possible, but
werenottestedinthepresentstudy.
2.3.Theexperiment
Theentireexperimentwasconductedindarkness
tosimulatenightconditionsandtoevokenight-
active behaviour (Thiele 1977, Lindroth 1985,
1986). However, since beetles probably cannot
apprehend red light (Mentzel 1979), a red dark
roomlight was used during parts of the experi-
ment,toenablevisualtrackingofthebeetles.Fur-
thermore,toenhancevisualisationofthesmaller
specimens,aminorwhitemarkingwasmadeon
theirelytra,byuseofadropofwhitecorrecting
fluid,fromacorrectingpen.
Allbeetleswereplacedinthemiddleofboth
arenasandwereconsequentlyusedtwice.Aspec-
imen was first put in test arena A (with bare
groundmiddle)andtheninB(withslashcovered
middle) or vice versa. The order, of which test
arena was first used, was randomized for each
specimen.Afteratestinthefirstarena,thespeci-
menwasinstantlyremovedtorestfor~1hour,
beforebeingusedagain.Foreachspecimen,tim-
ingcontinuedfor600secondsintotalandstarted
whenthebeetlespecimenstartedtomove,inany
direction. Total time spent in slash versus total
timespentonthebaregroundoutofthe600sec-
ondswastheonlyfactorrecorded.Nofurtherde-
Fig.2.Thetimeandspentinslash(outof600sec-
tailson theindividual’sparticular dispersalpat-
onds)whenreleasedinthemiddleofthetwotestare-
ternsormovingbehaviourswereobservedorre-
nas.–a.Pterostichusoblongopunctatus.–b.
cordedsincethepresentstudyisfocusedonthe
Carabushortensis.Percentiles(10,25,50,75and90)
beetle’s habitat choice in a setting composed of
areincludedineachbar.Thedashedlinedenotes
only two different options (i.e., high complex- meantimespent.
ity/slash covered vs. low complexity/bare
ground). for associations between carabid body weight
andtimespentinslash.Allanalyseswerecarried
out by use of the software package “SPSS for
2.4.Statisticsandanalyses Windows,version13.0”(SPSSInc.1989–2004).
Thedatasetwassmallandnotnormally distrib-
uted. Due to related samples (the time spent on 3.Results
bare ground versus in slash) non-parametric
Wilcoxon signed ranks tests were used. In the The time spent in slash for specimens of P.
analyses,mediantimespentinslash,splitbyspe- oblongopunctatus, released on bare ground
cies and release spot were used. Furthermore, (arenaA),weresignificantlyhigherthanthetime
Spearmanrankordercorrelationswereassessed spent on bare ground (Wilcoxon signed ranks
126 Nittérusetal. (cid:127) ENTOMOL.FENNICAVol.19
Table2.Thetimespentinslash(outof600seconds)bytheselectedcarabidspeciesafterreleaseintwotest
arenas(baregroundvs.slashcovered).Tableshowsmeanandstandarddeviation,minimum,maximumvalues
andpercentilesforeachcategory.
Releasespot N Mean(S.D.) Min./Max. Percentiles:
Median(25th/75th)
P.oblongopunctatus Bareground 12 481(166) 0/589 528(451/584)
Slashcovered 12 543(172) 0/600 600(578/600)
C.hortensis Bareground 13 432(256) 0/598 592(168/595)
Slashcovered 13 562(95) 275/600 600(588/600)
test,p=0.034)(Fig.2andTable2.).Andonce 2003). Consequently, a possible reason for the
again, when released in slash (arena B), P. non-significant result of C. hortensis when re-
oblongopunctatus specimens spent significantly leased on bare ground (arena A), in the present
moretimeinslashthanonthebareground(p= study,mightbeduetoitsimportanceasapredator
0.008)(Fig.2andTable2.). (orasasuccessfulcompetitor)forresources.Pos-
However, for C. hortensis specimens, re- sibly,C.hortensisdoesnotperceivebareground
leased on bare ground (arena A), no significant asriskyandstayssearchingforpreyhere,rather
difference (p = 0.51) were found, between time thansearchingforshelterfrompredators.
spent in slash compared to bare ground (Fig. 2 Anothertheoryforaspecificmovingbehav-
andTable2.).Still,whenreleasedinslash(arena iourorhabitatchoiceofsomearthropodsmight
B), C. hortensis specimens spent significantly beduetotheirspecificbody structure(e.g.size
more time in slash than on bare ground (p = and length of extremities), which could affect
0.001)(Fig.2andTable2.). theirlocomotiveabilityordispersalpatternsinor
Spearmanrankordercorrelations,showedno out of complex habitat structures (Farji-Brener
significant relationships between carabid body etal.2004).Consequently,onereasonableexpla-
weight and time spent in slash, neither for nation to our results would be that P. oblongo-
P. oblongopunctatus (0.191<p<0.646), nor for punctatus (which is the smaller species of the
C.hortensis(0.750<p<0.923). two),wouldmoveslowerandherebystaylonger
inslashpilesthanontheopengroundcompared
toC.hortensis.However,inthepresentstudy,we
4.Discussion analysed for this and found no associations be-
tweenbodysizeandtimespentinslash.
Theresultsofthepresentstudysupportearlierre- Inagermanstudy,carabidbeetleswereused
sultsshowingthatarthropodsrespondandreact tostudyeffectsofforestregenerationwithselec-
towards microhabitat complexity on the micro tive and small scale clear-cutting on the ground
scale(Thomas&Marshall1999,Traugott2002, andtheresultsshowedthatsmallopenings,cre-
Gunnarsson et al. 2004, Juen & Traugott 2004) ated after clear-cuttings, probably served as an
andmoreoverthatarthropodssometimesevenac- importantretreatforopenhabitatspeciesandthat
tivelyselectacertainhabitatpatchontheground forest species were preserved during the early
(Grez et al. 2005, Toews et al. 2005), or may phaseoftheforestregenerationprocess(Huber&
adapt specific moving behaviours or patterns in Baumgarten2005).Inthepresentstudywestud-
diverse habitats (Johnson et al. 1992, Jopp & iedtwoforestspecieswithsimilarhabitatprefer-
Reuter2005). ences but there is a possibility that the habitat
Thereareseveralpossiblemechanismsforas- preference needs further examination. Possibly,
sociationsbetweenabundance,distributionorac- extreme conditions of the structural complexity
tivity of arthropods and habitat complexity, for cantriggerorenhance,anorganisms’preference
instancedifferentinteractions,suchaspredation foracertainhabitat.Thiscouldexplainwhywe
pressure, between individuals (Buddle et al. foundadifferenceinbehaviourbetweenthetwo
ENTOMOL.FENNICAVol.19 (cid:127) Habitatchoiceoftwocarabids 127
species in our study although they are both re- Buddle,C.N.&Rypstra,A.L.2003:Factorsinitiating
garded as forest species. It has been suggested emigrationoftwowolfspiderspecies(Araneae:Ly-
cosidae)inanagroecosystem.—Environ.Entomol.
thatcarabidscanstillberestrictedtoratherspe-
32:88–95.
cificmicrohabitatpatchesinthefield(Greenslade
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Farji-Brener,A.G.,Barrantes,G.&Ruggiero,A.2004:
residuefromclear-cutssignificantlyaffectedthe
Environmentalrugosity,bodysizeandaccesstofood:
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atestofthesize-grainhypothesisintropicallitterants.
vascularplantsinborealforests. —Oikos104:165–171.
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117.
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sonsStiftelse,Wilhelm&MartinaLundgrensVetenskaps-
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