The Fijian Nesobasis: a further examination of species diversity and abundance (Zygoptera: Coenagrionidae)

2008·2.5 MB·English

by  Van Gossum, H

Odonatologica37(3):235-245 September1.2008
TheFijian Nesobasis: a furtherexamination
of species diversity andabundance
(Zygoptera: Coenagrionidae)
H.Van Gossum¹’*,C.D. Beatty²,M.Tokota’a³andT.N.Sherrat4t
1EvolutionaryEcologyGroup,University ofAntwerp,Groenenborgerlaan171,
B-2020Antwerp,Belgium
2GrupodeEcologiaEvolutiva,DepartaraentodeEcologiayBiologiaAnimal,
Universidad deVigo,EUETForestal,CampusUniversitario,ES-36005 Pontevedra,Galicia,Spain
3International Conservation,South Pacific Program,11Ma’afuStreet,Suva,Fiji
4DepartmentofBiology,Carleton University, 1125 Colonel ByDrive,Ottawa,
Ontario,K1S5B6, Canada
ReceivedJune11,2007/ReviewedandAcceptedOctober21, 2007
Recently,anoverview ofthediversity,abundance,distribution andmorphological
characteristics ofspp. ofthegenusNesobasis,endemictoFiji,waspresentedforspp.
occurringonthe2largestislands ofthearchipelago:VitiLevuandVanua Levu.Here,
thisknowledgeisextendedbyprovidingmoreextensivediversityandabundance data
fortheisland ofVanua Levu,aswellasfor4smallerislands inFiji: Taveuni, Koro,
Ovalauand Kadavu. Previous research indicated that the Nesobasis spp.inhabiting
VitiLevu andVanuaLevu areunique,withthese islands havingnospeciesin com-
mon.Thenewdataconfirmthisproposalandalso show thatsmallerislandsinprox-
imity tothese 2largerislands usuallycontainasubset ofthelargeisland’s Nesobasis
fauna. The island ofKoro, however,isunusual in that,while itsNesobasis spp.are
predominantlythose foundonVanuaLevu,it alsoharbours N.rufostigma,asp.oc-
curringonVitiLevu.Further, N.recavaisendemic toKadavu and isnotfoundon
VitiLevu,the nearestlargeisland. Speciesrichness ishigheronlargethan smallis-
landswhile meanspeciesabundances wereconsistentlyhigheronlargeislandscom-
paredtosmallislands. Thepatternofdistribution andspeciationinthisgenusisquite
complex, andisthesubject ofongoingresearch.
INTRODUCTION
The study of oceanic islands offers an excellentopportunity to explore the
process andpattern ofselectionas wellas thenature of speciation (DARWIN,
*Correspondingauthor:[email protected]
236 H. vanGossum, C.D.Beatty,M.Tokota'a&T.N.Sherratt
1859; MacARTHUR & WILSON, 1967). Sadly, in many island groups, par-
ticularly thosein the Southwest Pacific, our knowledge ofbasic biodiversity is
limited. Moreover,thereis afundamentallack ofinformationon thebehaviour,
lifehistoryandecology ofendemicislandfauna(WHITTAKER, 1998). Inthis
context BEATTYetal.(2007) reported informationonthe diversity,abundance
andbasic morphology ofspecies of thegenusNesobasis(Odonata: Zygoptera).
Notonly is thegenusNesohasisendemictoFiji, itisalso species-rich, withspe-
cies distributedoverseveral islandswithinFiji (DONNELLY, 1990). Moreover,
for someofthe species withinthe genus,malesare seldomobservedat oviposi-
tionsites(VAN GOSSUM etah, 2007). Thismalerarity hasnot causedsex role
reversal as previously speculated (DONNELLY, 1990, 1994)butresearch is on-
going to explore whatfactorsmayexplain malerarity in somespecies ofNeso-
basisbut not inothers (seealso VANGOSSUM etal.,2007).
Inour previous report, based on research conductedin 2005 (BEATTY et
al.,2007), wefocussed onNesohasis observedon Viti Levuand partsofVanua
Levu. Duringourresearch in2006wewereableto exploreotherregions onVan-
ua Levuandalso to include informationonspecies diversityandabundancefor
four additionalsmaller islands: Kadavu, Koro,Ovalau and Taveuni.For these
fiveislands weprovide quantitative estimatesof Nesohasis species diversityand
abundance.Furthermore,as BEATTY etal.(2007) didforotherspecies, wepro-
videbasic morphological characteristicsforfieldidentificationforone described
species (N. recava) andfora newspecies weencountered(Uds3). We also make
note ofany reproductive behaviour(tandem,copulation wheel,andoviposition)
observed forthesespecies.
In thispaperwe characterisetheinter-island distributionofspeciesof Nesoha-
sis basedprimarily onour ownobservational data,butalso onearlierpublished
work (DONNELLY, 1990;BEATTY etal„ 2007). Theislands ofTaveuniand
Koroare locatedclosertoVanuaLevu(the secondlargest islandinthearchipel-
ago) than Viti Levu (the largest island inthe archipelago), while theislands of
Ovalau andKadavu are located nearerto Viti Levu (Fig. 1). Ifsmallerislands
sharespecies with nearby largerislands, weexpected the Nesohasis community
on Taveuniand Koro tobea subsetofspecies occurring onVanuaLevu, while
OvalauandKadavu species were expected to occuralso on Viti Levu.
Many ecological factors can influencewhethera disperserfromthemainland
establishes onanisland. However, abundantspecies are morelikely to produce
higherabsolutenumbersofdispersers thanrarespecies(MacARTHUR &WIL-
SON, 1967;GASTONetal.,2006). Therefore,if dispersal played an important
role in determining establishmentsuccess, onemight expect that thosespecies
foundonsmallerislandswouldcomprise asubset ofthemoreabundantspecies
onthelarge island.
Speciesdiversity and abundance inNesohasis 237
METHODS
ThedamselflygenusNesobasisisabundant andwidespreadintheFijianislands.Theyarethedomi-
nantZygopterainmoststreamhabitats,particularlyinmountainstreams,buttheyarenotfound in
largeriversorponds(DONNELLY, 1990,1994).We usedtopographicmaps(1:50,000)in combina-
tion withourpriorexperiencewith thegenus(BEATTYetal.,2007)toselect regionsonislandsthat
werelikelytocontain appropriateNesobasis habitat. Inaddition,T.W. Donnellyand D.Polhemus
communicated theirearlierexperienceswithNesobasis onthedifferent islands.
TheFijiIslandsarelocated intheeasternMelanesian regionoftheSouth-westernPacificandhave
awarm,humidtropicalmaritimeclimatewithmeanmonthlytemperaturesfrom23°Cin Julyto27°C
in January(RYAN,2000).Theislands aresubequatorialandexposedtoheavierrainfall betweenNo-
vemberandApril,especiallyonthelowislandsandtheleewardsidesofthelargeislands(EVENHUIS
&BICKEL,2005).OurstudywasconductedduringthedryseasoninFiji fromAugust6toOctober4,
2006,atimeofyearsimilartothetimingofresearchsummarisedinBEATTYet al.(2007).Fijiconsists
ofseveralhundred islands andoccupiesatotalareaofapproximately650,000km2 ofwhichtheland
areaislessthan 3percent.There aretwolargeislands in thearchipelago(Fig.1):Viti Levu(10,388
km2)and Vanua Levu(5,535km2) (seealso EVENFIU1S& BICKEL,2005).Viti Levuand Vanua
Levuarerugged,withlandformsincludingvolcanicplugs,erodedcalderas,deepgorges,andravines
carvedbymountain streams,flat-bottomedvalleyswithextensivefood plains,andmangrovedominat-
ed deltas(EVENHUIS& BICKEL,2005).Otherislandsinthearchipelagoareconsiderablysmaller,
manyhavinglesspronouncedtopographyandlackingstreams.However,several islandsaresizable and
predominantlyvolcanic in
origin,havingsignificantel-
evations and most impor-
tantly mountain streams
that could hold species of
Nesobasis.Ofthesesmaller
islandswesampledKadavu
(408km2),Koro (109km2),
Ovalau(102km2)andTave-
uni (434km2).
Study sites that com-
pliedtoourselectioncrite-
ria (see further) forVAN-
UA LEVU(seeFig. 1)in-
clude: KR-01 (I6°30.79’S,
179°32.70’ E, alt.265m),a
largestreamonthe interi-
orroad above Korotesere,
crossingapproximately 1.2
kmsouthofSeavaciRd,we
sampledupstreamfromthe
road; KR-02 (16°28.55’S,
179°33.32’ E, alt. 170m),
second stream above Ko- Fig.I. Mapofsixislands ofFiji forwhich dataarepresented,showing
rotesere, we sampled on samplelocations. ForVANUA LEVU: (1)KR-01;- (2)KR-02; -
thedownstreamside ofthe (3)NagaciCreek;— (4)VunigautulailaiCreek;— (5)WR-01.ForTA-
road crossing;NagaciCre- VEUN1:(6)Somosomo;—(7)TV-02.ForKORO:(8)BuretiniCreek;
ek(16°28.36’S,179°35.32’ - (9)K-01; - (10)K-02.ForOVALAU:(11)Lovoni.ForKADAVU:
E, alt. 130m),smallstream (12)VuniseaEast.Sitedescriptionsandlatitude/longitudecoordinates
crossing road near small areprovidedinthetext.
238 H.vanGossum, C.D.Beatty,MTokota'a&T.N.Sherratt
settlement,wesampleddownstream oftheroad; VunigautulailaiCreek (16°30.06’S, 179°37.20’ E,
alt. 110m), streamatbridgeonroad aboveVanuavou,wesampleddownstreamoftheroad;WR-01
(16°41.12’S, 178°55.29’E,alt.335m),riverathighelevation inwesternVanuaLevu.For TAVEUNI
(seeFig. 1)wesampled;Somosomo(16°46.40’S, 179°58.22’W, alt. 30m),alargeriveratthesouth-
ernedgeofSomosomovillage,wesampledupstream ofthebridge;TV-02 (16°44.12’S, I79°54.57’
W, alt.395m),small streamabove Somosomoinagriculturalarea.Wealso sampledatTavoroFalls,
in BoumaNational HeritagePark,asite thatwasindicated tobe verygood Nesobasis habitat (D.
Polhemus,pers. com.). Despitesearchinganhour with two persons wewere unable tolocate any
Nesobasis. ForKORO(seeFig. l)wesampledBuretini Creek(I7°15.82’S,179°22,08’E,alt. 150m),
astreamwith verylowflow, andpredominantlyexposedbedrock withboulders and numeroussmall
pools,wesampledimmediatelyabovealargewaterfall,workingupstreamtotheroad crossing;K-01
(I7°15.82’S, 179°22.08’ E,alt. 40m),astreamalongtheroad crossingthe interior oftheisland in
thenorth;K-02 (17°19.82’S, 179°25.92’E,alt. 50m), alargestreamontheeastside ofKoro,which
crossesthemain road southoftheintersectionwith theinterior roadacrossthenorth sideoftheis-
land.ForOVALAU(seeFig. I)wesampledLovoni (17°41.20’S,I78°47.38’ E,alt. 85m),arivernear
Lovoni village,high inthe caldera of theisland’s volcano. For KADAVU (seeFig. 1)wesampled
VuniseaEast(19°01.93’S, 178°10.79’ E,alt. 140m),alargestreamonthemain roadeast ofVunisea,
samplingupstream ofthebridgeinaregionwithmuchexposedbedrock,boulders andwaterfalls.
Oursamplingmethodconsisted ofnettingallobserved damselfliesatasite,identifyingeveryindi-
vidualbelongingtothegenusNesobasis.Wedecidedonlytoincludesitesforwhichsamplinglasteda
minimum ofonehourwithaminimum of2peoplesearching.Whileaone-hour sampleperiodmay
notbelongenoughtodetectallspeciespresentatasite(forexample,those that areveryrareorthat
may bepresentatthewateratdifferent timesofthedaythan thosesampled), this level ofsampling
effortallowed ustocharacterize thecommonspeciesataparticularsiteeffectively.Wehave alsocho-
sentoexclude sitesforwhich wesampledforonehouror greater,but whereoursampleeffortswere
focussed onthecaptureofparticularspeciesforourresearch; in these casessamplingeffortwould
not provideanunbiased sampleofspecies abundances atasite. For eachofthe sitesthat metour
criteria werecorded date,latitude and longitude,streamwidth and lengthofthe streamsampled,
and theapproximatesamplingduration (for2searchers). This information allowed ustocalculate
coarseabundance estimates; streamwidth and lengthwereused tocalculate areasampled(number
ofindividuals per unitofarea),while samplingtimeprovidedanalternativemeasureforcalculating
species abundances (numberofindividuals perunitoftime)(seealso BEATTYetal.,2007).
Analysis ofspecies distributions amongislands utilized aMann-WhitneyU Test(SPSS 13.0)to
determinewhether speciesoccurring bothonthelargeisland andoneormoreofthe smallerislands
differed inmeanabundances fromthose onlyoccurring onthelargeisland.
SPECIES DESCRIPTIONS
Thefollowing basicdescriptionsprovide characteristicsweusedinthefieldfor
species identification.In some instancesidentificationofspecies required mag-
nifying lenses(20X magnification) or a field-microscope, as a close lookat the
exactstructureofgenitaliaand/ormesostigmallaminaewas required(seeDON-
NELLY, 1990). Moredetaileddescriptions canbefoundin TILLYARD(1924),
DONNELLY(1990) and will appearin Donnelly unpubl. ms. With respect to
thelatterandas agreed uponwithT.W.Donnelly, inwhatfollowsweuse thefirst
letter(s) of thespecies namesDonnelly will be using inhis forthcoming manu-
script toallowconvenientcomparison (seealso BEATTYetal., 2007). Wefound
onespecies newto science during our samplingin 2006,whichwerefertoas un-
Species diversityand abundance in Nesobasis 239
describedspecies 3(Uds 3).Thisallowsfordistinctionbetweenthis species and
two species {Uds 1 and Uds2) discussedinBEATTY etal.(2007).
N. recava(DONNELLY, 1990):Kadavu.Thisis aslender, medium-sizeddam-
selfly,endemicto theisland. Thethoraxofmalesisbright bluelaterally,dorsal-
ly black, while femalesare morepale blueorbrownonthe lateralthorax. Fur-
ther,males are predominantly blueonthe dorsumofabdominalsegmentsnine
andten withbluecolourextending laterally, whilefemaleshavesomepaleblue/
brownonthedorsumofabdominalsegmentten and limited colorationon seg-
TableI
Speciesdiversity andabundance fornewlocationsvisitedonVanuaLevuin2006.Totalareasampled
andduration ofsamplingaregiveninitalics
LLooccaalliittyyaannddddaattee SSppeecciieess NNuummbbeerr ooff DDeennssiittyy DDeennssiittyy
iinnddiivviidduuaallss ((iinnddiivviidduuaallss//110000mm22)) ((iinnddiivviidduuaallss//hh))
KK..RR--0011 ((2277//0099)) 22225500mm22 110055mmiinn
NA.taall 2299 11..33 1166..66
NN..aauu 11 ~~00 00,,66
NN.. bbrraacchhyycceerrccaa 7788 33..55 4444..66
KN.ff 22 00..11 11..11
NN.. I1 2255 11..11 1144..33
NN..rr 55 00..22 22..99
UUddss33 33 00..11 11..77
KKRR--0022((2277//0099)) 11440000mm22 6600mmiinn
NN.aal! 4422 33 4422
NN..bbrraacchhyycceerrccaa 4422 33 4422
NN. cc I1I1 00..88 1111
NN.. I1 7755 55..44 7755
NNaaggaacciiCCrreeeekk((1177//0099)) 9900mm22 6600mmiinn
NN..aall 22 22..22 22
NN..aauu 22 22..22 22
NN..bbrraacchhyycceerrccaa 1100 I11I.I1 1100
NN..ff 22 22..22 22
NN..l1 44 44..44 44
NN.. vv 11 11..11 11
VVaanniiggaauuttuullaaiillaaiiCCrrkk(f1177//0099)) 770000mm22 6600mmiinn
NN..l1 33 00..44 33
WWRR--0011((2266//0099)) 11550000mm22 l1O0S5mmiinn
NN..aall 2255 11..77 1144..33
NN..aauu 33 22 11..77
NN..bbrraacchhyycceerrccaa 110055 77 6600
NN..ff 11 00.,11 00..66
NN. I/ 5599 33..99 3333..77
NN.rr 11 00,.11 00..66
240 H.vanGossum,CD. Beatty,M.Tokota'a&T.N.Sherratt
ment nine.Thepterostigma ofbothsexes is darkbrown. N. recava is somewhat
similarto N. selysionVitiLevu, though showing onaveragemoreextensiveblue
colorationon thoraxandabdomenthan inN. selysi(BEATTYetal„ 2007). We
didnot observeany matingassociationsorovipositions.
Uds 3:Vanua Leva. Thisis a very large damselfly, withextensive blue-green
colorationonthoraxandabdomen.Themale iseasily distinguished by thepter-
ostigma onitsforewings, whichareenlarged andhaveapearlescent pinkcolora-
tion.Femalesare generally blue-greenincolour, somewhatsimilarto femalesof
N. brachycerca, butlarger. Maleswere observed displaying to one another, but
notandemsoregg-laying wereobserved.
RESULTSAND DISCUSSION
In totalwesampled 27sites onfiveislands, collecting 886specimens ofNeso-
basis, with 12 sites meeting our criteria for inclusion(see Methods): 5 sites for
VanuaLevu(Tab. I), 2 forTaveuni(Tab. II),3 forKoro (Tab. Ill), 1 forOvalau
(Tab. IV)and 1 for Kadavu(Tab. V).Sitesthatdidnot meet ourselection criteria
containednospecies thatdidnot occurinnearby(withinisland) sites.Therefore,
our interpretation ofspecies distributionandabundancewouldnot bechanged
ifthesesites were included.
Fig. 2.VenndiagramofNesohasisspecies distributionsamongtheislands ofVitiLevu,VanuaLevu,
Ovalau,Kadavu, Koro and Taveuni. Species distributions arebased onBEATTYet at,2007and
present data,except forthefollowing;Nesobasisaurantiaca, N. caerulescens, N.flavostigma,N. ingens,
N. leveriand N.pedataonViti Levu,N. campioniandN. monticolaonOvalau(DONNELLY, 1990),
and N. tonTaveuni (J.H. Skevington,pers. com.).
Speciesdiversity andabundance inNesobasis 241
Weencountereda totalof9species fromthe 'VanuaLevu' group,whichwere
distributedoverVanuaLevu,Taveuniand Koro(see Fig. 2 forarepresentation
ofknown species distributions). All species foundon Taveuniwere also found
onVanuaLevu. ForKoro, thiswas notthecase: whereasmostspecies foundon
Koroarealso found onVanuaLevu,we additionally encounteredN. rufostigma,
aspecies occurring onViti Levu, butnotVanuaLevu(Tab. III).We didnot find
N. rufostigma to beabundanton Koro (only two specimens werecollectedat a
single location). ThefactthatKorois locatedata middledistance betweenViti
LevuandVanuaLevumayhelp toexplain thepresenceofspecies frombothViti
LevuandVanuaLevuthere.As notedearlier, VitiLevuandVanuaLevu donot
share species of Nesobasis(BEATTY etal., 2007andresults here included); at
present Korois theonly islandwhereNesohasisspecies of thetwo large islands
areknownto co-exist.
We encountered6species from the Viti Levu' group,foundon Ovalauand
Kadavu, (as wellas onKoro) (Fig. 2).All species encounteredonOvalau were
also foundonViti Levu.Species werecordedonKadavuwerealso foundonViti
Levu, except forN. recava., whichisendemictoKadavu (seealso DONNELLY,
1990). Our findings for Kadavu are similar to DONNELLY (1990), where the
samethree species were found.For Ovalau threeof thefivespecies also found
by DONNELLY(1990) were includedin our sample, whilewe didnot observe
N. campionior N. monticola.Flowever, we didfind Uds I onOvalau, whichhad
not previously been described for this island(Tab. IV). For Taveuni and Koro,
nopreviously published species accounts exist forcomparison.
SpeciesrichnessatsiteswithinTaveunivariedbetween2and3species, forKoro
itvariedbetween3and4species, forOvalau4species andforKadavu 3species.
Forboth VitiLevuandVanuaLevuthemostspeciose locationsharboured8spe-
ciesofNesobasis(BEATTY etal.,2007). Maximalspecies richness persitethus
appearshigher onthelarge islandscompared to thesmallislands.
Table II
Species diversity and abundance forlocations visited onTaveuni in 2006. Total areasampledand
durationofsamplingaregiven initalics
Localityanddate Species Number of Density Density
individuals (individuals/!00m2) (individuals/h)
Somosomo(3/10) 5500m2 60min
N. au 1 -0 1
N. 1 17 0.3 17
TV-02(3/10) 600m! 60min
N. hrachycerca 4 0.7 4
N. 1 1 0.2 1
N. v 3 0.5 3
242 H.vanGossum, C.D.Beatty,M.Tokota'a&T.N.Sherratt
Table III
Species diversity and abundance for locations visited onKoro 2006. Total area sampledand
duration ofsamplingaregivenin italics
LLooccaalliittyyaannddddaattee SSppeecciieess NNuummbbeerr ooff DDeennssiittyy DDeennssiittyy
iinnddiivviidduuaallss ((iinnddiivviidduuaallss//I1O0O0mm22)) ((iinnddiivviidduuaallss//hh))
BBuurreettiinnii CCrreeeekk((77//0099)) i1m00)0mm22 6600mmiinn
NA..bbrraacchhyycceerrccaa 44 00..44 44
NA.tf/ I1 00..11 11
NA.trruuffoossttiiggmmaa 22 00..22 22
NA..vv 44 00..44 44
KK.--0011 ((77//0099)) 220000mm22 6600mmiinn
NA.tbbrraacchhyycceerrccaa 66 33 66
NAt./f 66 33 66
NA.vv 88 44 88
KK--0022 ((88//0099)) 44000000mm22 II4400mmiinn
NA..bbrraacchhyycceerrccaa 11 ~~00 00..44
NAt./f 1133 00..33 55..66
NA.vv 11 ~~00 00..44
TableIV
Species diversityand abundance forlocations visited onOvalau in 2006. Total area sampledand
duration ofsamplingaregiveninitalics
LLooccaalliittyy aannddddaattee SSppeecciieess NNuummbbeerr ooff DDeennssiittyy DDeennssiittyy
iinnddiivviidduuaallss ((iinnddiivviidduuaallss//I1O0O0mm22)) ((iinnddiivviidduuaallss//hh))
LLoovvoonnii ((1155//0088)) 1111000000mm-2’ I13355mminin
NA. hheetleerroonneeuurraa 4422 00..44 1188..77
UUddss /I 2 ~-00 00..99
NA. rruuffoosstliiggmmaa 2233 00..22 1100..22
NN.. sseellyyssii 88 00..11 33..66
TableV
Species diversityand abundance forlocations visited onKadavu in 2006. Total areasampledand
duration ofsamplingaregivenin italics
LLooccaalliittyyaannddddaattee SSppeecciieess NNuummbbeerr ooff DDeennssiittyy DDeennssiittyy
iinnddiivviidduuaallss ((iinnddiivviidduuaallss//I1O0O0mm22)) ((iinnddiivviidduuaallss//hh))
VVuunniisseeaaEEaasstt((2222//0099)) 33550000mm11 I10055mmimn
NN.. llounnggiisstiyyllaa 44 00..11 22..33
NN..rreeccaavma 6655 11..99 3377..11
NN..rruuffoosattiiggmmaa 66 00..22 33..44
Speciesdiversityandabundance in Nesobasis 243
Fig. 3.Species/arearelationship(log/log)forspeciesofNesobasisontheislands ofViti Levu,Vanua
Levu,Ovalau,Kadavu,Taveuniand Koro. An overallpositive correlation between islandsize and
speciesrichnessisobserved.
Comparing totalknownspecies diversityperisland(Fig. 2),thetwolarge islands,
Viti LevuandVanuaLevacurrently have20 and11 knownspecies, respectively.
Thetotalspecies diversityofthe foursmall islandsis: 4forKoro, 5 forTaveuni,
6forOvalauand3 forKadavu (DONNELLY, 1990;BEATTYetal., 2007; J.H.
Skevington, pers.com.anddataherein).Considering theirsmallersizeandrela-
tive isolationfrom VitiLevu andVanuaLevu(see Fig. 1) the lowerspecies di-
versity of thesefourislands isnot surprising (e.g. MacARTHUR& WILSON,
1967).Aspecies/area curve (Fig. 3)comparing islandsize versus species number
(log/log transformations) shows an overall positive correlationbetween island
sizeandspecies richness (R =0.833,df= 4, P=0.039). Itshouldbe notedthat
Kadavu, withits greatdistancefromViti Levucompared to Ovalau, isthe only
smaller islandhavinganendemic, N.recava. Species relationships andthepattern
ofspeciation withinandbetweenislandsare thesubjectsof current phylogenetic
research,
Apositive relationship between species abundanceandspecies range size/oc-
cupancyhasbeenidentifiedinarangeoffloraandfauna(GASTON etal., 1997;
GASTON etal.,2000). Thisrelationship hasalsobeenfoundto holdforspecies
assemblages distributedon andamong islands(GASTON etal.,2006). On the
large islandsin Fiji,Viti LevuandVanuaLevu,this general pattern alsoappears
to holdfor species of Nesobasis, withrelativelyabundantspecies also being en-
counteredat alarger numberofsites (BEATTY etal., 2007 and data herein).
Betweenislands, thispatternis lessclear. Wecompared themeanabundancesof
large islandspecies foundonadjoining small islandsto large islandspecies not
foundonsmallislands. Whenconsidering combineddatafrom Viti Levu versus
Ovalauand Kadavu, and VanuaLevu versus Taveuniand Koro(all abundance
datainBEATTYetal.2007(tabs 1&2,pages22-23,25)andallabundancedata
244 H.vanGossum, C.D.Beatty,M.Tokota'a&T.N.Sherratt
fromVanuaLevu(Tab, I) herein), therewas littleevidencethatspecies foundon
oneofthelargeislandsandatleastonesmallislandhadhighermedianabundance
thanthosespecies foundonly on thelarge islands.(Mann-Whitney U = 62.0,N
- 25, P=0.406) (Fig.4).Whilequestions couldberaisedaboutthepowerofthis
test, itsupportsthe general pattern seen in our species distributiondata;while
some“common”species onthelarge islandsare likely tobefoundonsmalleris-
lands, species such as N. monticola, rare onViti Levubut foundonOvalau, and
N.f,rare onVanuaLevubutlocally abundanton Koro, suggest thatthis is not
ahardandfastruleforNesobasis.
Thedatapresented here greatly expand our knowledge on Nesohasis species
distributionandabundance, particularly forTaveuni, Koro, Ovalau and Kada-
vu, fourislandsforwhichdistributionand abundancedatawerenot previously
published. As indicatedin BEATTYet al.(2007) the damselfly faunaofFiji re-
mainsrelatively unexplored. Indeed,in total, threespecies previously unknown
to scienceresultedfrom our sampling(BEATTY etal.,2007anddataherein). It
Fig. 4. Box and whisker plot ofmeanspecies abundances (individuals/lOOm2).Values arefor (a)
populationsofspeciesfound onlyononeofthe twolargeislands ofVitiLevu orVanua Levu(large
island only), (b)largeisland populationsofspeciesfoundonthelargeislands andatleastonesmall
island,(c) smallislandpopulations.Thedarklinewithin thebox represents the median,whiletheup-
per and lowerboundaries ofthe boxrepresentthe 75lhand 25"'percentiles,respectively. Theextent
ofthe upperwhisker representsthe90,hpercentile, while theextent ofthe lowerwhisker represents
the 10thpercentile.Dotsrepresent anyobservations outsideofthese ranges. Anon-significanttrend
isobserved wherein speciesfoundon the largeislands and atleast oneadjoiningsmallisland have
higherabundances inlarge-islandpopulationsthanthosefoundonlyonthelargeisland.Smallisland
populationshaveconsistentlylowerabundances than largerisland populations.