Carabid (Coleoptera) assemblages in the Scottish uplands: the influence of sheep grazing on ecological structure

2006·0.24 MB·

by  Lorna Cole

©EntomologicaFennica.11October2006
Carabid (Coleoptera) assemblages in the Scottish uplands:
the influence of sheep grazing on ecological structure
LornaJ.Cole,MegL.Pollock,DuncanRobertson,JohnP.Holland&DavidI.McCracken
Cole, L. J., Pollock, M. L., Robertson, D., Holland, J. P. & McCracken, D. I.
2006:Carabid(Coleoptera)assemblagesintheScottishuplands:theinfluenceof
sheepgrazingonecologicalstructure.—Entomol.Fennica17:229–240.
AsaresultoftheEuropeanCommunityCommonAgriculturalPolicyreformin
2005itispredictedthatlivestockgrazingintheScottishuplandswillbecomeless
intensive.Ateachoftwouplandresearchcentres,twolarge(>40ha)plotswere
establishedtoinvestigatetherelationshipbetweengrazingintensityintheScot-
tishuplandsandbiodiversity.Oneplotwasgrazedintensivelybysheepwhilethe
otherwasgrazedextensively.Groundbeetlesweresampledbypitfalltrappingto
determinetheinfluenceofgrazingpressureontheecologicalmake-upofground
beetleassemblages.Grazingintensitydidnotsignificantlyinfluencecarabiddi-
versity.However,grazingintensity,altitudeandmoisturedidinfluencethecara-
bidecologicalassemblagestructureatbothlocations.LargeflightlessCarabus
speciesweremoreabundantinextensivelymanagedplotsthanintensivelyman-
agedplotsatbothlocations.Itislikelythattheselong-living,relativelyimmobile
beetleswerefavouredbythegreaterstabilityofthevegetationstructureintheex-
tensivelygrazedplots.Monitoringtheecologicalassemblagestructureprovides
amoresensitiveapproachthandiversityindiceswhencomparingtheimpactof
grazingandagriculturalmanagementbutisalsorobustenoughtoallowdirect
comparisonsbetweendifferentgeographicallocations.
L.J.Cole,D.RobertsonandD.I.McCracken,LandEconomyandEnvironment
ResearchGroup,ScottishAgriculturalCollege,Auchincruive,Ayr,KA65HW,U.
K.;Email:[email protected]
M.L.PollackandJ.P.Holland,HillandMountainResearchCentre,Scottish
AgriculturalCollege,KirktonFarm,Crianlarich,FK208RU,U.K.
Received2November2005,accepted26May2006
1.Introduction which is determined by historical support pay-
ments received by each farm. Thelink between
The European Common Agricultural Policy subsidies and production has consequently bro-
(CAP) has recently been reformed resulting in ken,andasaresultagriculturalmanagementwill
major changes in the way farming in the EU is no longer focus simply on maximising produc-
supported (Leguen de Lacroix 2003). Subsidies tion.Consequently,itispredictedthatagriculture
which were previously production orientated willbecomemorelinkedtomarketdemandsand
(e.g. based on the number of grazing animals), thatchangesin agriculturalsubsidieswillresult
have been replaced by a Single Farm Payment in, among others, changes in grazing manage-
230 Coleetal. (cid:127) ENTOMOL.FENNICAVol.17
ment.InScotland,itispredictedthatgrazingin- nature frequently disturbed, and several studies
tensity in the Scottish uplands will be signifi- haveshownthatlargeflightlesscarabidsaremore
cantly reduced as a result of the CAP reform abundantinextensivelymanagedhabitats(Blake
(Cook2004).Thereisconcernthatthiswillhave etal.1994,1996,Riberaetal.2001).Changesin
anadverseimpactonuplandvegetationandthe grazingpressureandmowingintensity notonly
wildlifeassociatedwithgrazedopenhabitats. affectthedisturbancefrequencyofahabitatbut
Changestolivestockgrazingpracticesinflu- alsothevegetationstructureandpreyavailability,
encethevegetationstructureandcompositionat whichinturnmayinfluencetheecologicalstruc-
bothpatchandlandscapelevelsandthisinturn ture of carabid assemblages. Extensively man-
alters ground beetle assemblages and diversity agedgrasslandistypicallyassociatedwithricher,
(Luff&Rushton1989,Dennisetal.1997).Cara- morestructurallydiversevegetationwhencom-
bidbeetlesareoneofthemostcommonfamilies paredtointensivelymanagedgrassland(Marriott
of surface-active arthropods in the agricultural 2004),andconsequentlymayfavourherbivorous
landscapeandarethoughttobepotentialindica- carabids such as Harpalus, Bradycellus and
tors of disturbance, as they are ubiquitous and Amara species. Intensively managed grassland,
easilysampledusingpitfalltraps,aresensitiveto ontheotherhand,hasbeenfoundtofavourCol-
environmental factors, and are morphologically lembola specialists as a result of an increase in
and ecologically diverse (Lövei & Sunderland prey abundance and a more open vegetation
1996,Niemeläetal.2000).Thesebeetleshavean structurefacilitatingthesevisuallyhuntingpred-
importantroleinthefarmlandecosystem,asthey ators(Riberaetal.2001).
arenotonlyimportantpolyphagouspredatorsof Cole et al. (2002) classified ground beetles
awiderangeofagricultural pests (Thiele1977, intosevenecologicalgroups.Theprimaryobjec-
Lövei&Sunderland1996),butalsoformanim- tiveoftheworkreportedherewastousetheeco-
portant dietary component for many decreasing logicalgroupsofColeetal.(2002)todetermine
farmland birds (Holland & Luff 2000). While whethergrazingpressureintheScottishuplands
monitoringtheinfluenceofgrazingintensityon influencestheecologicalmake-upofgroundbee-
theabundanceofdifferentspeciesisvaluablein tleassemblages. This study thus focused on the
its own right (Eyre et al. 1989, Rushton et al. influenceofgrazingpressureintheScottishup-
1989, Purvis et al. 2001), findings at different lands on the ecological structure of carabid as-
geographicallocationsarerarelydirectlycompa- semblages and evaluated the robustness of this
rableduetodifferencesintheindividualspecies approachformonitoringenvironmentalimpactat
presentateachlocation.Monitoringregimesthat differentgeographicallocations.
focus on the ecological structure of a beetle as-
semblagearelesslikelytobesensitivetothere-
quirements of individual species and conse- 2.Materialandmethods
quentlymaybemorerobustthanregimeslooking
atspeciescomposition(Willbyetal.2000).Fur- 2.1.Studysites
thermore,byclassifyingassemblagesonthebasis
oftheirecologywegainabetterinsightintotheir Fourlarge(>40ha)uplandgrazedplotswerees-
ecological functioning (Whittaker 1975) which tablishedattwoScottishuplandresearchstations:
mayinturnhelpustopredicthowanecosystem Kirkton (Perthshire) and Sourhope (The Bor-
will respond to future disturbance (Diaz & Ca- ders).Thetworesearchcentreswereseparatedby
bido1997). adistanceof184km.Twoadjacentplotsateach
Life-history traits are strongly linked to the researchstationwereeachallocatedtooneoftwo
frequency of habitat disturbance and large, im- sheepgrazingintensities:anextensivelightsum-
mobilespecieswithalowfecunditytendtobefa- mer-onlygrazingandanintensivemoderateyear-
vouredinundisturbedhabitatswhilesmall,mo- roundgrazing(Table1).Thegrazingintensities
bilespecieswithahighfecunditytendtobefa- weresetbytakingintoaccountthetypeofforage
vouredindisturbedhabitats(Southwood1988). available in each of the plots. Grazing regimes
Intensively managed grassland habitats are by werestartedinJune2001atKirktonandOctober
ENTOMOL.FENNICAVol.17 (cid:127) Grazingintensityandcarabidcommunitystructure 231
Table1.Grazingtreatmentsatthetworesearchcentres.
Site Nat.GridRef. Plotsize Altitude Grazing Opento
livestock
Kirkton,Intensive NN370306 44.4ha 390–590m 1–2sheepha–1 Jan–Dec
Kirkton,Extensive NN368303 40.8ha 390–600m 1–1.3sheepha–1 Jun–Oct
Sourhope,Intensive NT846217 74.9ha 270–470m 3–3.7sheepha–1 Jan–Dec
Sourhope,Extensive NT843211 49.7ha 260–420m 3sheepha–1 Jun–Sep
2002atSourhope.Theaimoftheintensivegraz- Using the HFRO sward stick (Barthram
ingregimewastocreatearelativelyshort,homo- 1986)25swardheightsweresampledwithin25
geneous,less-tussockysward.Theaimoftheex- cmofeachsideofatransectlinecorrespondingto
tensiveregimewastocreateastructurallydiverse the line of pitfall traps. Mean sward height (in
swardwithdistincttussockandinter-tussockar- cm),swardheterogeneity(standarderrorofvege-
eas. Atotalof40locations(i.e., 10withineach tation height), transect evenness (abundance of
plot)weresampledin2003andafurther20loca- the dominant species), transect diversity (Shan-
tions (i.e., 5 within each plot) were sampled in non-Wienerindex)andtransectspeciesrichness
2004.Eightofthe2003locationsatSourhopebe- werecalculated.
cameencroachedwithbrackenandwereconse- A map was produced of the vegetation
quently relocated in 2004. Sampling locations patchesina30mdiametercirclecentredonthe
were chosen to represent the range of altitudes, middlepitfalltrap.‘Patch’wasdefinedasanarea
vegetationtypesandstructureswithineachplot ofvegetationofsimilarspeciescompositionand
andwereaminimumdistanceof8mapart. structure,distinctfromadjacentvegetation.The
plantcommunity ofeachofthepatcheswasre-
corded, and 25 or 50 sward heights were mea-
2.2.Invertebratesampling suredfromeachofthemainpatches.Thenumber
ofpatches,numberofplantcommunities,within-
Groundbeetlesweresampledusingpitfalltrap- patchspeciesrichness,patchmeanswardheight,
ping.Trapsconsistedofplasticbeakers(75mmin patchvegetationheterogeneity(standarderrorof
diameter and 100 mm deep) partly filled with patchvegetationheight),patchperimeterlength
100% monopropylene glycol as a killing agent andpatchheightratio(maximumpatchheightdi-
and preservative. To prevent small mammals videdby theminimumpatchheight)weremea-
from entering the traps and to limit damage by sured.
livestock,a15mmmeshgridwassecuredover
thetrapmouthwithametalstaple(Downieetal.
2000).Ateachsamplinglocationa16mrowof 2.4.Physicalattributes
ninepitfalltraps(2minter-trapdistance)wases-
tablishedatthebeginningofMay.Thetrapswere Duringthepitfallsamplingperiod,foursoilcores
leftinsituforaperiodoffourweeksandthesam- (6 cm diameter and 10 cm deep) were taken at
ple from each row of 9 traps was collected and randomfromeachlineofpitfalltrapsandthesoil
pooledinJune. wassubjectedtostandardsoilanalysestodeter-
mine: pH,% moisture content,% organic matter
content, phosphorus availability (mg/l) and po-
2.3.Vegetationsampling tassium availability (mg/l). Information on the
soil penetrability (blf/in2) was collected using a
Ateachsamplinglocation,vegetationheightand soilpenetrometer.Inadditiontheslopeangle(de-
species composition were measured between grees),theaspect(degreesfromNorth),andthe
JuneandAugusteachyearattwospatialscales: altitudeofeachpitfallsamplinglocationwerere-
thetransectlevelandthewiderpatchlevel. corded.
232 Coleetal. (cid:127) ENTOMOL.FENNICAVol.17
Table2.SpeciesinventoryfortheintensiveandextensivelygrazedplotsatKirktonandSourhope(E=extensive,
I=intensive).Theecologicalgroupofeachspeciesisprovided(seefootnote).
Species Ecologicalgroup Sour- Kirk- Sour Kirk-
hope,E ton,E hope,I ton,I
Calathusfuscipes Mediumnocturnalpredators X – X –
Cychruscaraboides Mediumnocturnalpredators – X – X
Harpalusrufipes Mediumnocturnalpredators X – – –
Nebriabrevicollis Mediumnocturnalpredators X X X X
Patrobusassimilis Mediumnocturnalpredators – X – X
Patrobusatrorufus Mediumnocturnalpredators – X – X
Pterostichusadstrictus Mediumnocturnalpredators X X X X
Pterostichusaethiops Mediumnocturnalpredators X X X X
Pterostichusmadidus Mediumnocturnalpredators X X X X
Pterostichusmelanarius Mediumnocturnalpredators X – X –
Pterostichusniger Mediumnocturnalpredators X X X X
Carabusarvensis Carabusspp. – X – X
Carabusglabratus Carabusspp. – X – –
Carabusnemoralis Carabusspp. X X X –
Carabusnitens Carabusspp. – X – X
Carabusproblematicus Carabusspp. X X X X
Carabusviolaceus Carabusspp. X X X X
Amaraaenea Diurnalherbivores X – X –
Amaracommunis Diurnalherbivores X X X –
Amarafamiliaris Diurnalherbivores X – X –
Amaralunicollis Diurnalherbivores X X X X
Loricerapilicornis Collembolaspecialists X X X X
Notiophilusaquaticus Collembolaspecialists X – – –
Notiophilusbiguttatus Collembolaspecialists – X X X
Agonumassimile Smallnocturnalpredators – X – X
Calathusmelanocephalus Smallnocturnalpredators X – X –
Pterostichusrhaeticus Smallnocturnalpredators X X X X
Agonumfuliginosum Small/mediumpredators – X X X
Agonumgracile Small/mediumpredators – – X –
Agonummuelleri Small/mediumpredators – X X X
Bembidionguttula Small/mediumpredators – – X –
Bembidionunicolor Small/mediumpredators – – X –
Clivinafossor Small/mediumpredators – X X X
Elaphruscupreus Small/mediumpredators – X X X
Elaphruslapponicus Small/mediumpredators – X – X
Elaphrusuliginosus Small/mediumpredators – X – X
Leistusrufescens Small/mediumpredators – – X –
Pterostichusdiligens Small/mediumpredators X X X X
Pterostichusstrenuus Small/mediumpredators X X X X
Pterostichusversicolor Small/mediumpredators – X X X
Trechusobtusus Small/mediumpredators – X X X
Harpaluslatus Nocturnalherbivores – X – X
Trichocellusplacidus Nocturnalherbivores X – – –
Agonumpiceum Insufficientinformation – – X –
Bradycelluscollaris Insufficientinformation – – X –
Carabusgranulatus Insufficientinformation – X – X
Elaphrusriparius Insufficientinformation – X – X
Harpalusquadripunctatus Insufficientinformation X – – –
Totalspeciesrichness 23 33 32 30
Totalcarabidabundance 1145 1207 1235 1436
ThesegroupscorrespondtoColeetal.(2002)ecologicalgroupsasfollows:Mediumnocturnalpredators–Group1,Carabusspecies–Group2,Diur-
nalherbivores–Group3,Collembolaspecialists–Group4,Smallnocturnalpredators–Group5,Smalltomediumpredators–Group6,Nocturnal
herbivores–Group7.
ENTOMOL.FENNICAVol.17 (cid:127) Grazingintensityandcarabidcommunitystructure 233
2.5.Statisticalanalysis tionofthecompositionofgroundbeetleassem-
blages,theyprovidelittleinformationontheeco-
The9pitfalltrapscollectedateachlocationwere logical structure of the community. To obtain
pooled prior to carabid identification. For each comprehensive information on the ecological
sampling year the following measures of diver- makeupofthecarabidassemblagesateachloca-
sitywerecalculated:thenumberofgroundbeetle tion,therelativeabundanceofgroundbeetleeco-
species(S)tomeasurespeciesrichness,Berger- logicalgroups–asdescribedbyColeetal.(2002)
Parkerdominanceindex(d)tomeasureevenness –wascalculatedforeachsamplinglocation(Ta-
and Simpson’s diversity index (N2) to measure ble2).Fivespecies(ofthe48speciescollected)
overalldiversity.Magurran(1988)recommends thatlackedsufficientecologicaldatawereomit-
combiningdiversityindicestoobtainamoreac- ted from these analyses (Table 2). All omitted
curatepictureofdiversitythansimplyconsider- specieswereextremelyrare,andconsequentlyit
ingoneortwooveralldiversityindices.Priorto is unlikely that their omission influenced the
the analyses, diversity indices were log-trans- analyses.Two-wayANOVAswereconductedon
formedwhererequiredtoapproachnormalityof thearcsin-transformeddataforeachresearchsta-
thecompareddistributions.ANOVAswerecon- tionindependentlytodetermineifgrazinginten-
ducted(ateachresearchstationindependently)to sityandyearofsamplinginfluencedtheecologi-
determinehowyearofsamplingandgrazingre- calmakeupofthegroundbeetleassemblages.
gimeinfluencedgroundbeetlediversity.The20 Canonical Correspondence Analysis (CCA)
newlocationssampledin2004,andthebracken was conducted for each research station inde-
locations sampled in 2003 at Sourhope were pendently to determine the principal environ-
omittedfromthisanalysis.Wheresignificantdif- mentalcomponentsdrivingtheecologicalassem-
ferences were indicated by ANOVA, Tukey’s blagestructure.CCAswereconductedontherel-
post hoc tests were applied to locate the differ- ativeabundanceofecologicalgroups.Atotalof
ences. 20 continuous environmental variables and one
Whilediversityindicesprovidesomeindica- categorical variable (Grazing Intensity) were
Table3.EnvironmentalvariablestakenintoconsiderationinCCA.
Environmentalvariable Description
Moisture Soilmoisturecontent%
Organicmatter Soilorganicmattercontent%
pH SoilpH
Phosphorus Availabilityofphosphorusinthesoil(mg/l)
Potassium Availabilityofpotassiuminthesoil(mg/l)
Penetrability Soilpenetrability(blf/in2)
Aspect Aspectofthepitfalltraps(degreesfromnorth)
Altitude Altitudeofthepitfalltraplocation(m)
Slope Slopeofthepitfalltraplocation(degrees)
Grazingintensity Grazingintensityofplot(intensiveorextensive)
Transectheight Transect:meanswardheight(cm)
Transectheterogeneity Transect:standarderrorofvegetationheight
Transectrichness Transect:numberofplantspecies
Transectevenness Transect:%abundanceofthedominantplantspecies
Transectdiversity Transect:Shannon-Wienerindexofvegetation
Patchratio Patch:maximumvegetationheightdividedbyminimumvegetationheight
Numberofpatches Patch:numberofdifferentvegetationpatches
Numberofcommunities Patch:numberofdifferentvegetationcommunities
Patchrichness Patch:numberofspeciesinpatch
Patchlength Patch:thetotalpatchedgelength
Patchheterogeneity Patch:standarderrorofmeanpatchheight
234 Coleetal. (cid:127) ENTOMOL.FENNICAVol.17
considered in the analyses (Table 3). Environ-
mentalvariableswerenormalisedbylogarithmic
transformation where required. The eight
brackenencroachedlocationsatSourhopewere
omittedfromthisanalysisduetoinsufficientveg-
etationdata.Aforwardselectionprocesswasuti-
lisedandonlyvariablesfoundtobestatistically
significant(atthe5%level)bytheMonteCarlo
Permutation test were included in the analyses,
thus reducing problems associated with multi-
collinearity(terBraak&Šmilauer2002).
Fig.1.Mean(+SD)relativeabundanceofCarabus
speciesandCollembolaspecialists(Group2and4,
3.Results respectively)onintensivelyandextensivelygrazed
plotsatKirktonandSourhope.
Atotalof2,643carabidsconsistingof33species
werecollectedfromKirktonand2,380carabids nificantly more species being recorded in 2003
consistingof36speciesfromSourhope(Table2). than2004(Table4b).
At both research stations, large, immobile
beetlesofthegenusCarabusweremoreabundant
3.1.Influenceofmanagementandsampling on extensively managed plots than intensively
yearondiversityandecologicalgroup managedones(Table4a–b,Fig.1).Therelative
abundance of Carabus species at Kirkton was
Two-way ANOVAs (Table 4a–b) indicated that overtwotimeshigherintheextensiveplotthan
grazing intensity did not influence the species the intensive plot, while at Sourhope the differ-
richness (S), evenness (d) or overall diversity ence was even more profound with almost a 5
(N2) of the carabid assemblages at Kirkton or fold increase in relative abundance between the
Sourhope.AtKirkton,theyearofsamplinghad intensiveandextensiveplots.Thisdifferencewas
noinfluenceonanyofthediversityindicesstud- found despite Carabus species being predomi-
ied, while at Sourhope a significant year effect nantlyautumnbreedersandhencepotentiallyless
wasfoundforcarabidspeciesrichnesswithsig- active in spring when the samples were taken.
Fig.2.Theecological
make-upoftheinten-
sively-andextensively-
managedplotsat
KirktonandSourhope.
ENTOMOL.FENNICAVol.17 (cid:127) Grazingintensityandcarabidcommunitystructure 235
Table4.Resultsof2-wayANOVAforgroundbeetlediversityandrelativeabundanceofdifferentecological
groupsatKirkton(a)andSourhope(b).LocationofsignificantdifferencesfoundusingTukey’sposthoctests(p
<0.05).n/a=notanalysedduetoinsufficientdata.
a)Kirkton
Index/Group Treatment(df=1,36) Year(df=1,36)
SpeciesRichness(S) F=1.53,p=ns F=0.26,p=ns
Berger-Parker(d) F=0.95,p=ns F=2.60,p=ns
Simpson's(N2) F=0.93,p=ns F=2.75,p=ns
Mediumnocturnalpredators F=0.01,p=ns F=2.70,p=ns
Carabusspp. F=7.17,p=0.01(Ext>Int) F=0.53,p=ns
Diurnalherbivores n/a n/a
Collembolaspecialists F=24.57,p<0.001(Ext<Int) F=1.07,p=ns
Smallnocturnalpredators F=1.82,p=ns F=4.27,p<0.05(2003<2004)
Small/mediumpredators F=0.48,p=ns F=3.20,p=ns
Nocturnalherbivores F=0.08,p=ns F=0.12,p=ns
b)Sourhope
Index/Group Treatment(df=1,20) Year(df=1,20)
Speciesrichness(S) F=0.01,p=ns F=5.34,P=<0.05(2003<2004)
Berger-Parker(d) F=0.62,p=ns F=0.85,p=ns
Simpson's(N2) F=0.11,p=ns F=0.33,p=ns
Mediumnocturnalpredators F=0.09,p=ns F=0.05,p=ns
Carabusspp. F=10.75,p<0.005(Ext>Int) F=1.35,p=ns
Diurnalherbivores F=0.73,p=ns F=2.17,p=ns
Collembolaspecialists F=0.00,p=ns F=1.58,p=ns
Smallnocturnalpredators F=0.03,p=ns F=2.51,p=ns
Small/mediumpredators F=0.87,p=ns F=1.57,p=ns
Nocturnalherbivores n/a n/a
The only other ecological group influenced by were well represented at Sourhope but largely
grazingintensitywasCollembolaspecialists.At lackingatKirkton.Despitedifferencesintheeco-
Kirkton,therelativeabundanceofthisgroupwas logicalmakeupoftheassemblagesatthetwore-
fourtimeslowerintheextensivelymanagedthan search station, consistent trends in the relative
intheintensiveplot(Table4a,Fig.1).AtSour- abundance of Carabus species were found be-
hope, no difference was observed between the tweenextensivelyandintensivelymanagedplots
twograzingtreatments(Table4b,Fig.1). (Fig.2).
Therelativeabundanceoffunctionalgroups
inthepitfalltrapsappearedtobefairlyconstant
betweensamplingyearswithonlysmallnoctur- 3.2.Influenceofenvironmentalfactors
nalpredatorsatKirktonbeinginfluencedbysam- ontheecologicalassemblagestructure
plingyear.Thisgrouphadahigherrelativeabun-
dancein2004thanin2003(Table4a,Fig.1).This CCAfortheSourhopedataproducedeigenvalues
indicatesthattheecologicalassemblagestructure of 0.318, 0.18, 0.07 and 0.03 for axes 1–4, ac-
was relatively consistent between sampling countingfor26.7%,15.7%,5.9%and2.7%ofthe
years. total variation in ecological structure, respec-
Cleardifferenceswerefoundintheecological tively (Fig. 3). CCA for the Kirkton data pro-
make-upofcarabidassemblagesatKirktonand duced eigenvalues of 0.124, 0.070, 0.025 and
Sourhope (Fig 2). Small nocturnal predators 0.004foraxes1–4,accountingfor22.9%,12.9%,
dominated the community at Kirkton, while at 4.7%and0.7%ofthetotalvariationinecological
Sourhopethecommunitywasdominatedbyme- structure, respectively (Fig. 4). The low eigen-
dium sized nocturnal predators. Furthermore, valueswereexpected,astheordinationwascon-
small to very small diurnal herbivore species ducted on only seven ecological groups as op-
236 Coleetal. (cid:127) ENTOMOL.FENNICAVol.17
Fig.3.CCAtriplotfortheKirktonecological-grouprelative-abundancedatashowingintensiveandextensive
sites,carabidecologicalgroups(blacktriangles;seeTable2),continuousenvironmentalvariables(vectors)and
intensityasacategoricalenvironmentalvariable(blacksquareboxnearorigin).Onlyenvironmentalfactorssig-
nificantatthe5%levelareincludedinthegraph(seeTable5).
Fig.4.CCAtriplotfortheSourhopeecological-grouprelative-abundancedatashowingintensiveandextensive
sites,carabidecologicalgroups(blacktriangles;seeTable2),continuousenvironmentalvariables(vectors)and
intensityasacategoricalenvironmentalvariable(blacksquareboxup-and-rightfromtheorigin).Onlyenviron-
mentalfactorssignificantatthe5%levelareincludedinthegraph(seeTable5).
posedtoalargenumberofindividualspecies.For AtKirkton,theCCAshowedaclearsepara-
bothlocations,axes1and2accountedformostof tion of intensively vs. extensively grazed plots
thevariationintheecologicalstructureofcarabid alongaxis2(Fig.3).AtSourhope,thedifference
assemblages. between the intensively and extensively grazed
ENTOMOL.FENNICAVol.17 (cid:127) Grazingintensityandcarabidcommunitystructure 237
Table5.InfluenceofenvironmentalvariablesoncarabidecologicalassemblagestructureasindicatedbyCCA.
OnlyfactorsfoundsignificantintheMonte-Carlopermutationtest(p<0.05)areshown.
Environmentalfactor Kirkton Sourhope
Slope F=8.00,p<0.001 –
Grazingintensity F=5.25,p<0.005 F=3.92,p<0.005
Altitude F=5.05,p<0.005 F=12.96,p<0.005
Moisture F=4.37,p<0.01 F=4.92,p<0.05
Phosphorusavailability F=3.18,p<0.05 –
pH – F=4.39,p<0.05
Organicmatter – F=3.21,p<0.01
Transectdiversity – F=2.57,p<0.05
plotswasnotsoapparent(Fig.4).Theseparation pressurecontributedtothisdifferenceinvegeta-
ofsamplinglocationsalongaxis1wasprimarily tionstructure.
aconsequenceofaltitude.Thelower-altitudelo-
cationsinboththeintensivelyandtheextensively
grazedplotshadhigheraxis1scoresthanhadthe 4.Discussion
higher-altitude locations. At Sourhope, sheep
grazing was more intensive at the foot of both Grazing intensity in the uplands can influence
plots where the vegetation was more nutritious carabidsatboththespeciesandassemblagelevel
than on the poorer quality vegetation found at (Dennisetal.1997;Luff&Rushton1989).Habi-
higheraltitudes. tataffinityofdifferentspeciescandifferbetween
At Kirkton, five environmental variables various geographical locations. Species de-
(Slope,GrazingIntensity,Altitude,Moistureand scribedbyThiele(1977)asbeingstrictlywood-
Phosphorus Availability) significantly influ- landspecieshavealsobeenassociatedwithlong
encedtheecologicalstructureofthegroundbee- grass,heathormoorlandintheU.K.(Luff1998).
tle assemblage, while at Sourhope six environ- Consequently, findings at the species level are
mentalvariables(Altitude,OrganicMatter,Graz- rarelytransferabletodifferentgeographicalloca-
ing Intensity, Moisture, pH, Transect Diversity) tions.Diversityindices,beingunrelatedtotheac-
did so (Table5). Threeenvironmental variables tualspeciespresent,mayprovideamorerobust
influenced ecological structure at both research way of monitoring the influence of agricultural
stations (i.e., Grazing Intensity, Altitude and managementacrossdifferentgeographicalloca-
Moisture) indicating the potential of these vari- tions.Diversityindiceshavebeenwidelyusedin
ablestobeusedaspredictorsofecologicalstruc- carabid studies (Kromp 1989, Luff & Rushton
ture. 1989,Bhriainetal.2002,Shahetal.2003)with
AtKirkton,vegetationattributesdidnotinflu- manystudiesindicatingahighercarabiddiversity
encethecarabidecologicalassemblagestructure in extensively than intensively managed fields
indicatingtheimportanceofsoilandtopography. (Luff&Rushton1989,Blakeetal.1996,Kromp
AtSourhope,thediversityofthevegetationatthe 1989).Whiletheuseofdiversityindicesmaybe
transect level, significantly influenced the eco- robust,muchoftheecologicalinformationislost.
logicalstructure.AtSourhope,theloweraltitude Bysolelylookingatthediversityofacommunity
samplinglocationsonbothplotsweredominated wemayrisktooversimplifythedataandconse-
byAgrostisspecies(i.e.,A.caninaandA.capil- quentlylooseinformationthatmaybeapparentat
laris), while the higher altitude locations were a finer scale. The use of ecological groupings
dominatedbymosaicsofAgrostisspecies(i.e.,A. couldprovideausefulwayofretainingsuchin-
caninaandA.capillaris)andNardusstricta.Itis formationwhileallowingrobustcomparisons.
likelythatacombinationofaltitude,soilfactors Inthisstudy,grazingintensitydidnotsignifi-
(e.g., soil pH and organic content) and grazing cantly influence carabid diversity but it influ-
238 Coleetal. (cid:127) ENTOMOL.FENNICAVol.17
enced the ecological structure, indicating that relative abundance of Collembola specialists at
monitoringattheecologicallevelwasmoresen- Kirkton was related to an increase in the abun-
sitive than monitoring diversity. Large species danceofprey.
belongingtothegenusCarabushadahigherrela- Thevegetationdiversityofintensivelyman-
tiveabundanceinextensivelymanagedplotsthan aged grassland tends to be more impoverished
on intensively managed ones. These findings (bothintermsofthenumberofspeciesandstruc-
wereconsistentnotonlybetweensamplingyears, turaldiversity)thanthatofextensivelymanaged
butalsobetweenthetworesearchstations.Blake grassland(Marriott2004).Thisheldtrueforthe
etal.(1994),Riberaetal.2001andTietze(1985) studysiteswherevegetationdiversity(measured
also found that extensively managed grassland bytheShannon-Wienerindex)wasricherinthe
habitatsfavouredlargercarabids,andColeetal. extensivelymanagedplotswhencomparedtothe
(2002)foundthattheabundanceofCarabusspe- intensively managed plots. It may therefore be
cies was greater in heather moorland and semi- predicted that diurnal and nocturnal herbivores
natural grassland than on intensively managed wouldbemoreabundantintheextensivelyman-
grass and arable land. Šustek (1987) found that agedplots.Thomasetal.(2001)foundthather-
urbanisationhadasignificantinfluenceoncara- bivorouscarabids(i.e.,HarpalusandAmaraspe-
bid body size with more urban areas having cies)wereassociatedwiththebotanicallydiverse
higher numbers of small species while undis- fieldmarginsinintensivelymanagedagricultural
turbedhabitatshadhighernumbersoflargesed- land,andthesespecieshavealsobeenshownto
entaryspecies.Itwouldthereforeappearthatthe be associated with weed cover in arable crops
relative abundance of large flightless carabids (Holland&Luff2000).Grazingintensity,how-
(e.g.,Carabusspecies)mightprovidearobustin- ever,didnotsignificantlyinfluencenocturnalor
dicator of habitat disturbance. It is likely that diurnal herbivores in this study. Herbivorous
large,long-living,flightlessbeetlesarefavoured carabids tend to favour vegetation associated
bythegreaterstabilityinvegetationstructurethat withdungpatches(Dennisetal.1997)andconse-
accompaniesextensivegrazingpracticesandare quentlytheyarelikelytohaveapatchydistribu-
less well adapted to the fluctuating conditions tionmakingaccuratesamplingdifficult.
characteristic of intensively grazed sites. Most Despitetheecologicalstructureofthecarabid
largeCarabusspeciesareautumn-breederswith assemblagesbeingquitedifferentatthetwoloca-
over-wintering larvae and (at least in Scotland) tions, changes in the relative abundance of
two-year breeding cycles (Ribera et al. 1999). Carabus species between extensive and inten-
Immobilespecieswithlong-lifecyclesrequirere- sively managed plots were consistent. Monitor-
sourcesthatarestableovertime. ingmethodsthatlookattherelativeabundanceof
In agreement with the findings of other au- Carabusspeciesarethereforerobustand,atleast
thors(Riberaetal.2001,Coleetal.2002),Col- inthisstudy,weremoresensitivethandiversity
lembola specialists had a higher relative abun- indices. Thereisconsensusintheliteraturethat
danceinintensivelygrazedlocationsatKirkton agricultural disturbance adversely influences
whencomparedtoextensivelygrazedlocations. larger carabids and consequently it is possible
The same trend was not observed at Sourhope. that the influence of management on Carabus
Collembolaspecialistspreferamoreopensward species could simply be the result of their large
asthisfacilitateshuntingbyvisualcues.Itispos- size.Whilesizemaybeasuitablesubstitutefor
sible that intensive grazing resulted in a more ecological groupings, and indeed would be far
openswardstructureatKirktonthanatSourhope simplertodetermineforspeciesnotintheorigi-
hencefavouringCollembolaspecialists.Ouror- nalclassificationbyColeetal.(2002),itislikely
dinations, however, indicated that vegetation that monitoring methods looking simply at size
characteristicsdidnotinfluencethecarabideco- distributionswouldbelesssensitive.Forexam-
logicalstructureatKirktonandgrazingintensity ple,itishighly unlikely thatmethodsanalysing
andaltitudeappearedtobetheprincipalenviron- carabidassemblagessimply onthebasisofsize
mental factors influencing Collembola special- distributionwouldhavepickeduptheinfluence
ists. Consequently it is possible that the higher ofmanagementintensityonCollembolaspecial-