Post on 04-Jul-2020
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ThemarchoftheCommonGreenIguana(Iguanaiguana):earlyestablishmentin
SingaporeandThailandisfacilitatedbythepettradeandrecreationalparks
MatthijsP.vandenBurg1*,StevenM.VanBelleghem2,ChristinaN.DeJesúsVillanueva3,4
1DepartmentofBiogeographyandGlobalChange,MuseoNacionaldeCienciasNaturales,SpanishNationalResearchCouncil,Madrid,Spain2DepartmentofBiology,UniversityofPuertoRico,RíoPiedras,SanJuan,PuertoRico3CollegeofEnvironmentalandLifeScience,UniversityofRhodeIsland,Kingston,RhodeIsland,USA4InternationalInstituteofTropicalForestry,UnitedStatesForestService,UnitedStatesDepartmentofAgriculture,SanJuan,PuertoRico*Correspondingauthor.email:thijs.burg@gmail.com.
Abstract
ThepopularityoftheCommonGreenIguana(Iguanaiguana)asapethascontributedto
itsglobaloccurrenceasaninvasivealienspecies.Earlydetectionandcontrolofinvasive
alienI.iguanapopulationsisnecessarytopreventtheneedforlargeandfinancially
demandingeradicationactions.Here,wecollatedinformationfromdigitalfootageand
interviewsregardingsightingsoffreeroamingI.iguanaspecimensinSingaporeand
Thailand,andpresentevidenceofearly-stageinvasionsandestablishment.Using
speciesdistributionmodeling,wefindthatlargepartsofThailandandneighboring
countrieshavesuitablehabitat,whichcouldfacilitatetheexpansionofthesealien
populationsifleftuncontrolled.Additionally,wereportsingularI.iguanasightingsin
HongKongandPeninsularMalaysia.WecallforawarenessofalienI.iguanainthe
PhilippinesduetothehighnumberofpetiguanasandreportedCITESimportationsas
wellastheavailabilityofsuitablehabitatthroughoutthearchipelago.Further,we
identifyI.iguanapresencetobefacilitatedbythereleaseofpet-tradedspecimensand
uncontrolledexhibitionpracticesinrecreationalparks.Weproviderecommendations
forimplementingmonitoringanderadicationeffortsandstrategyrecommendationsto
haltfuturespreadandrelease.
Keywords:CITES,Citizenscience,Invasivealienspecies,Legislation,Rangeexpansion,
Socialmedia,Wildlifetrade
Introduction
TheCommonGreenIguana(Iguanaiguana,Linnaeus,1758)isaheavilytradedreptilian
petspeciesthathasseenitsglobaltransportregulatedsince1977(CITES2019).Despite
regulation,thepettradeisanimportantcontributortotheoriginofinvasive
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populations(Falcónetal.2013;Bocketal.2018;DeJesúsVillanuevaetal.under
review),althoughotherintroductionfacilitatorsareknown(Censkyetal.1998;vanden
Burgetal.2020).IguanaiguanaoccursthroughoutCentralandSouthAmericaaswellas
onseveralCaribbeanislands(Stephenetal.2013;Bocketal.2018).InvasionsofI.
iguanaaremainlyrestrictedtoCaribbeanislands,withonlyasmallsetofislandsknown
fromoutsidethisregion:CanaryIslands(Spain),Fiji,Hawaii(USA),JapanandTaiwan
(Bocketal.2018;Leeetal.2019).Importantly,establishedpopulationsofthisinvasive
alienspecies(IAS)haveneverbeensuccessfullyeradicated(Leeetal.2019;Rivera-
MilánandHaakonssoninpress).
TherapidgrowthofI.iguanapopulationscanposeathreattotheeconomyof
invadedterritories,throughinfrastructuredamageandagriculturalloss,aswellas
threatstobiodiversity(Bocketal.2018).Asinvasivepopulationscanoriginatefrom
multiplegeneticlineages(Stephenetal.2013;vandenBurgetal.2018a;DeJesús
Villanuevaetal.underreview)highgeneticdiversitymightincreaseadaptivevariation
topersevereinnon-nativeenvironments(Kolbeetal.2004).InPuertoRico,and
presumablyotherinvasiveareas,I.iguanapopulationgrowthmaybefurtheraidedbya
lownumberofpredatorsanddirectcompetitors(López-Torresetal.2011).
Furthermore,invasiveI.iguanapopulationsareathreattonativespeciesthroughdirect
competitionandhybridization(Vuillaumeetal.2015;Mossetal.2018;vandenBurget
al.2018b;vanWagensveldandvandenBurg2018).OnGrandCayman,anislandof196
km2,thepresentinvasiveI.iguanapopulationwasestimatedtoreachbetween0.9–1.9
millionindividualsinearly2018beforethestartofagovernment-financedculling
program(Rivera-MilánandHaakonssoninpress).Duringthisprogram'sinitialyear,
throughcollectiveworkof500hunters,over960,000iguanaswereremovedagainstthe
expenseof5.7millionUSD(Rivera-MilánandHaakonssoninpress).Topreventfurther
spreadofthisspeciesandtheneedformultimillion-dollareradicationprograms,rapid
managementactioniskeyduringtheinitialintroductionandestablishmentphase
(Davis2009;Blackburnetal.2011).
InsoutheastAsia,ThailandandSingaporeareconsideredimportanthubsinthe
internationalwildlifetrade(Nijman2010),withherpetofaunalsurveyreportshaving
identifiednotablediscrepanciesamongCITESimportdata,andthepresenceofseveral
non-nativespeciesinthewildinthesecountries(NijmanandShepherd2007,2010,
2011;YeoandChia2010;PooleandShepherd2016).ForThailand,Nijmanand
Shepherd(2011)foundthatover150distinctspeciesofamphibiansandreptileshad
CITESimportrecordsbetween1990–2007.Incontrast,onlytworeptiles(Trachemys
scriptaelegansandI.iguana)wererecordedinThailandduringa2011–2012inventory
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ofwildalienvertebratefauna(Boonkuawetal.2014).ForI.iguana,Boonkuawetal.
(2014)reportedthreesightingsofsinglespecimensinThailand,allofwhichhad
disappearedbeforethereport’spublication.Singaporeismainlyregardedasanimport
andre-exportcountry(Nijmanetal.2012)andwasthemainregionalreptileimporter
between1998–2007(Nijman2010).IncontrasttoThailand,over20alienreptile
specieswerepresentinSingaporein2010(YeoandChia2010).Ofthesespecies,only
fourwereconsideredestablished(Calotesversicolor,Pareasmargaritophorus,
SiebenrockiellacrassicollisandXenochrophisvittatus);withI.iguanaknownfromonlya
fewscantrecordings(Chua2007;YeoandChia2010).However,despiteprevious
reportsoffewI.iguanaspecimens(YeoandChia2010;Boonkuawetal.2014),recent
reportsoffree-roamingI.iguanaonsocialmediaplatforms(e.g.FaceBookand
Instagram)andoniNaturalisthavesparkedourconcernoverthepotentialfor
establishedandgrowinginvasivealienpopulationstobepresentinSingaporeand
Thailand.Here,we1)summarizethecurrentextentofIguanaiguanainSingaporeand
Thailand,2)identifylocationswithsignsofearlyestablishmentanditsfacilitators,3)
predictthepotentialrangeintheabsenceoffutureeradicationaction,and4)provide
recommendationstopreventfuturereleasesandmitigatenegativeecologicaleffects.
Methods
Observations
WetracedthepresenceofalienI.iguanainSingaporeandThailandthroughverifiable
sightingsusingphotographsandvideosfromsocialmedia(FaceBookandInstagram),
Internetwebsites(www.flickr.com,www.istockphoto.com,www.shutterstock.com)and
iNaturalist.Wecontactedandinterviewedownersofonlineimageswhosecontent
suggestedthepresenceoffree-roamingI.iguanatoacquiremoredetailsincludingthe
locationwherethepicturewastaken,date,presenceoffreeroamingI.iguana,presence
ofdifferentI.iguanalifestagesandnumberofindividualspresent.Throughsnowball
sampling(whereintervieweeshadmorefootageorcontactswithsimilarfootage)we
wereabletoacquireadditionalverifiablesightingsnotpublicallyavailable.When
imagesweretakenwithinzoosorrecreationalparks(hereafterrecreationalparks)we
askedwhetherI.iguanawerekeptinholdingcagesorwerefreelyroaming.Inthelatter
case,werecordedthesefacilitiesaspotentialsourcesforcurrentandfutureinvasive
populations.
Suitablehabitatmodeling
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TobetterunderstandthepotentialrangeofIguanaiguanainSingaporeand
Thailandaswellassurroundingcountries,weusedMaxEnt(Philipsetal.2018)as
implementedinthedismoRpackage(Hijmansetal.2017;RCoreTeam2019)tobuild
speciesdistributionmodels(SDM),forcurrentandfutureclimatescenarios.MaxEnt
usesenvironmentalandclimaticdatafromspeciesoccurrencelocalitiestobuilda
predictiveSDMofhabitatsuitability(HS)forthestudyspecies,whichrunsbetween0
(lowsuitability)and1(highsuitability).First,weacquiredI.iguanaoccurrencedata
uploadedtotheGlobalBiodiversityInformationFacility(GBIF2019)andiNaturalist.We
filtereddatarecordsbasedongeoreferenceinaccuracy(excludedwhen>50km),added
recordscollectedduringrecentfieldworkbytheauthors(forColombiaandPuertoRico)
andfromrecentpublicationsoninvasivepopulations(Kraus2019;Leeetal.2019),as
wellaslocationsinSingaporeandThailandwherehatchlingorjuvenileI.iguanahave
beenobserved.Weremovedduplicatedlocationsandobviouslyerroneousrecordsfrom
locationswithoutI.iguanabreedingpopulations(e.g.Galapagos)andwithaltitude
recordsoutsideofthespeciesrange(>1000meters;Stephenetal.2013).Remaining
recordswerethenfilteredtoretainonlyonerecordper50km2(Boriaetal.2014)to
removedistributionskewnessinlocalitydata,leavingatotalof420recordsforfinal
modelconstruction.Weretainedoccurrencedatafromestablishedalienpopulations
arguingthat,althoughinvasiveareascanholddifferentclimaticcompositionscompared
tonativeareas,localclimaticvariablesaresuitableforsuccessfulreproductionandthus
helptogeneralizeintraspecificvariationwithinI.iguana(Elithetal.2010;Briscoe
Runquistetal.2019).
TheinitialSDMmodelwasbuiltusinguncorrelatedWorldClim2.0bioclimatic
variablesandaltitudelayer(FickandHijmans2017;at2.5arc-minutesresolution).As
correlationbetweenvariablescanleadtooverfitting,weimplementedthevifstep
functionwithinthesdmpackage(NaimiandAraújo2016).Thisstepwiseprocess
identifiesthevarianceinflationfactor(VIF),ameasureofhowmuchonevariablecanbe
explainedbytheothers,foreachvariableandremovesthosewithhighVIFvalues(here
setto10;ChatterjeeandHadi2006).Afterstepwisefiltering,10variableswereretained
forthefinalmodelwitha2.0–9.1rangeofremainingVIFscores:meandiurnalrange
(BIO2),isothermality(BIO3),meantemperatureofwettestquarter(BIO8),mean
temperatureofdriestquarter(BIO9),precipitationofwettestmonth(BIO13),
precipitationofdriestmonth(BIO14),precipitationseasonality(BIO15),precipitationof
warmestquarter(BIO18),precipitationofcoldestquarter(BIO19),andaltitude.
Bioclimaticandoccurrencedatawerenextcombinedtobuildapresence-only
SDMusingMaxEnt(Philipsetal.2018)forboththecurrentandafutureclimate
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scenario.ThesemodelsweregeneratedforsoutheastAsia,aswellasthePhilippines
giventhehighnumberofI.iguanafootageonsocialmediaplatforms.PredictionsofHS
forafutureclimatescenariowererunfor2050usingtheACmodelandrcp45for
greenhousegasemission(FickandHijmans2017).Forboththecurrentandfuture
climatescenario,asetof10SDMreplicationswererunwith80%ofrecordsusedfor
modeltrainingand20%formodeltesting.Modelperformancewasevaluatedusingthe
areaunderthecurvesummarystatistic(AUC)withone-tenthofthedata;AUCvaluesof
≥0.90indicatehighmodelperformance(Swets1988).TheHSabsencethresholdwas
determinedfromthetrainingspecificityandsensitivityasimplementedinthedismo
package(Hijmansetal.2017).
Results
ForThailand,sightinginformationwascollectedfromcontactwith15personsand
iNaturalistforrecordssince2016.Sightingsoriginatedfromatotalof12locations
distributedthroughoutThailand(Fig.1)withaminimumnumberoftotalsightingsof97
I.iguana(TableA1,SupportingInformation).Adultorsubadultlifestageswere
observedatalllocations,whereashatchlingorjuvenilelifestagesoccurredatfour
locations.Thehighestnumberofsightingsbydifferentobserverswasfoundaround
NakhonRatchasimatown(Thainame:����������)inNakhonRatchasima
province.LocationswiththehighestnumberofuniqueI.iguanawereNakhonSi
ThammarathandUbonrat,andintheUthaiThanidistrict.Lastly,atleastfour
recreationalparksexhibitnon-cagedI.iguana:ChaiNatBirdPark,ChiangMaiNight
Safari,NakhonRatchasimaZoo,andThaLatBirdPark.
ForSingapore,sightinginformationwascollectedfromiNaturalistrecords,
contactwith10persons,andfromsevenuniquegreyliteraturepublicationssince2007
(Chua2007;Yeo2014;NgandLim2015;Tay2015;Khoo2016;ChewandLow2017;
Yeo2019).Werecordedaminimumof50I.iguanasightingsfrom17locationsin
Singapore(Fig.1),ofwhichfivelocationsshowedpresenceofhatchlingsand/or
juveniles.ThehighestnumberofI.iguanasightingscomesfromtheareasurrounding
JuronghillandJurongBirdParkaswellasaroundtheWarrenGolf&CountryClub.
Recreationalparkswerenotfoundtoexhibitfree-roamingI.iguanainSingapore.
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Fig.1LocalitieswithpresenceofIguanaiguanain(A)Thailandand(B)Singaporeshowingnumberofiguanasandyearofsighting.Colorofthemostrecentyearisdisplayedperlocation.
Besidesfree-roamingI.iguanarecordsfromSingaporeandThailand,we
recordedtwoadditionallocationsinsoutheastAsia.First,onefreeroamingadultI.
iguanawasobservedsoutheastofKualaLumpur,PeninsularMalaysia;thisanimalwas
caughtintheyardoftheobserverandwasreleasedinanareanearby.Thesecond
recordisfromtwofreeroamingadultiguanasadjacenttotheTsingTamReservoirsin
HongKong.
TheSDMsforbothcurrentandfutureclimaticconditionssuggestthepresence
ofsubstantialareawithI.iguanasuitablehabitatinThailandandsurroundingcountries
(Fig.2andFig.A1).Suitablehabitatisespeciallypresentinmainlandregionsbelow15
degreeslatitude,exceptforsomeareasinThailand,southandcentralPeninsular
Malaysiaandnon-coastalregionsinVietnam.Severalhigherlatituderegionshave
suitablehabitataswellincludingpartsoftheGulfofMartaban,andlowerelevation
areasinThailand,southernLaos,andcentralVietnam.Undera2050climatescenario
HSinonlysomeareaswillsubstantiallychangewithlessareasoflowerHSintheGulfof
Martaban,PeninsularMalaysiaandSumatra(Fig.A1,SupportingInformation).AllI.
iguanalocationsreportedherebelow14degreeslatitudeareinhighHSareas,with
thoseathigherlatitudesinareaswithmarginalorlowHS,exceptfortheUthaiThani
district(Fig.2).ForthePhilippines,thecurrentclimatemodelidentifiedsuitablehabitat
inlowlandareasonallmajorislandsandmarginalhabitatorabsenceofsuitablehabitat
forhigherelevations,especiallyonMindanao.ThemedianAUCfor10SDMreplications
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forcurrentclimaticconditionswas0.944(50%interquartilerangesof0.942–0.946),
withamedianHSabsencethresholdof0.21;andforfutureclimateconditions(2050)
0.948(50%interquartilerangesof0.942–0.951)andmedianHSthresholdof0.28.
Fig.2SpeciesdistributionmodelsforIguanaiguanainSingapore,Thailandandsurroundingcountries.Modelsusedanabsencethresholdof0.17andhabitatsuitabilityrangesfromhigh(darkred)tolow(white).BluedotsrepresentlocationswithI.iguanapresence
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Discussion
WereportI.iguanainvasionsandearlyestablishmentinbothSingaporeandThailand
withdetailsaboutpopulationsizeaswellasthecurrentandpotentialfuture
distribution.Inbothcountries,thepresenceofhatchlingand/orjuvenilelifestages
indicateslocalrecruitmentandongoingestablishmentofthisknowninvasivealien
species(IAS).Importantly,thisreportdescribesthesecondrecordedmainland
establishmentofI.iguana,andincreasesthenumberofknownnon-westernhemisphere
establishmentstosix;Hawaii,Fiji,Japan,Singapore,ThailandandTaiwan(Mitoand
Uesugi2004;Engemanetal.2011;Falcónetal.2013;Kraus2019;Leeetal.2019);
thoughupdatesonthestatusoftheJapaneseandHawaiianpopulationsarenecessary.
Followinginterviews,weidentifiedthelikelysourceoftheseinvasionstobepet-trade
animalsthateitherescapedorwereintentionallyreleasedbyownersorunsecurely
exhibitedinrecreationalparks.BesidesthereleaseofpetI.iguanaduetotheirsize,
anothermotivecanbefangsheng;theBuddhistactofreleasingliveanimalsbelievedto
buildspiritualmerit(NgandLim2010).AsI.iguananativelyoccursinsub-tropicaland
tropicalbiomesidenticaltothosefoundthroughoutsoutheastAsia(Olsonetal.2001),
weexpectcontinuedspreadandgrowthofthesealienpopulationsintheabsenceof
mitigationactions.Indeed,ourcurrentandfutureclimateSDMsindicatethatlargeareas
intheregionhavehighlysuitableI.iguanahabitat.Additionaltoover-landdispersaland
facilitatedbythisspecies’swimandraftcapabilities(Censkyetal.1998;Breuil1999;
vanVeen2011;F.Kraus,pers.comm.2020),throughover-waterdispersalalarge
numberofnovellocationswithsuitablehabitatcouldbereachedfromSingapore(Fig.
2):PeninsularMalaysia,Sumatra,and>3,000islandsoftheIndonesianRiau
archipelago.Intheabsenceofremovalactions,thepersistenceanduncontrolledgrowth
ofI.iguanapopulationsisevidentasnumerouslocationsarewithinhighlysuitable
habitatandrecruitmentispresent(Fig.2).Thecasepresentedherecallsforimmediate
managementactionas1)establishmentstillappearstobeinanearlyphase,2)
eradicationexpensesarerelativelylow,3)currentrecordsarelikelyanunderestimate
asdatawerecollectedopportunisticallybynon-iguanaspecialists,4)alarge
uncontrolledI.iguanapopulationcouldhavefarreachingconsequencesfornative
biodiversity.
Knowledgeontheinvasionpathwayandsourceofalienpopulationsis
importanttopreventrepetitive(un)intentionalincursions.AlthoughI.iguanaisnative
totheAmericantropics,theirimportation,captivebreedingandescapeorrelease
practicescouldleadtounmanageablepopulationgrowthinsoutheastAsia.Between
2000and2017,atotalof1,254liveI.iguanawereimportedintoThailand(importer
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reportedquantity;CITES2019),thoughcurrentlythenumberofiguanaspresentcould
arguablybehigherduetoincountrycaptivebreedingpracticesaswellasknownimport
discrepanciesinCITESreporting(NijmanandShepherd2011).ForSingapore,542live
specimenshavebeenreportedbyimporterspre-2004(CITES2019),withnorecords
since,likelyduetothecountry’sillegalizationonpetownership.Severalinterviewees
statedthateithertheythemselvesorothers(i.e.,iguanafarms,recreationalparksor
privateresidence)havereleasedcaptiveiguanas.Thiswasinadditiontodeliberate
releasestatementsbysocialmediausers.Increasingthepublicawarenessofthe
negativeeffectsfromIASpopulationsmayhelptodiscouragefuturereleases.
Uncontrolledorflawedexhibitionpracticesofanimalscanleadtotheirescape.
InSpain,Fàbregasetal.(2010)identifiedthatenclosuresecuritywasnotsufficientto
preventescapein14%ofassessedenclosures,mainlyforenclosuresholdingalien
species,whichmightsourceIASpopulations.ForThailand,basedonthepresenceof
free-roamingiguanasclosetoThairecreationalparksthatexhibitnon-cagediguanas,
thesefacilitiesarethemostlikelysourcesofiguanasreportedfromatleasttwoareas:
NakhonSiThammarathandNakhonRatchasima.InSingapore,althoughwedidnot
acquireinformationaboutrecreationalparksthatexhibitfree-roamingiguanas,grounds
ofonepark(JurongBirdPark)areinvadedbyiguanas.Anecdotalevidencesuggeststhat
theirpresenceintheparkandsurroundingareasoriginatesfromtheformer
neighboringreptilerecreationalpark(JurongReptilePark).Inadditiontotheriskof
escapefromparks,free-roamingI.iguanawithinrecreationalparksarereproductively
unhindered,whichleadstonestingandsuccessfulrecruitment.Fromsuchnests,small
freeroaminghatchlingsemergecapableofestablishingoff-groundpopulations.This
posesaparticulardetectionchallenge.Ontopoftheirsmallsize,thelizards’green
colorationallowsthemtoinconspicuouslyblendinwiththefoliage,evadingdetection
foruptoayearintotheirdevelopment.Incontrasttoadults,thesehatchlingsareharder
tocatchandtrackgiventheirsmallsizeandcapacitytodisperse>200mwithinone
monthafterhatching(KnappandAbarca2009).
WithlittleinformationavailableforAsianI.iguanaintroductions,itisnot
possibletomakestraightforwardpredictionsabouttheecologicalimpactsofthese
novelestablishments.Datafromthewesternhemispheredemonstratesthepossibility
thatestablishedpopulationscanspreadpet-tradediseasestonativespecies(Hellebuyk
etal.2017),competitivelydisplacenativespecies(vandenBurgetal.2018b),andcause
erosionanddamagetoagriculturalfields,roadsandairplanes(López-Torresetal.
2011).InThailandwenotethatinvasivepopulationscouldhavethecapacitytodisplace
Physignathuscocincinus,theChinesewaterdragon(IUCNstatusVulnerable;Stuartetal.
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2019),givenitssmallermaximumsnout-ventlength(SVL)andecologicalnicheoverlap
betweenthespecies.Namely,P.cocincinusisalsoanarboreallizardthatresidescloseto
streamsineastandsoutheasternThailand(Stuartetal.2019).Further,hatchling
iguanaswilllikelybepredatedbynumerousnativespeciesgiventhehighregional
snakediversity(Chan-Ardetal.2015),thoughpredatorsforadultI.iguana(whichcan
reach>45cmSVL)arefew(e.g.largePythonbivittatusorMalayopythonreticulatus
[Lowetal.2016]).Additionally,I.iguanamightcompetewithnativespeciesfor
territory(Chua2007)andnestingsites(e.g.Varanussp.).However,dataonthe
reproductivecycleofI.iguanainSingaporeandThailandiscurrentlylacking,making
reproductiveperiodcomparisonswithnativespeciesdifficult.Nevertheless,imagesof
matingiguanasaswellasareleaseddevelopedeggsuggestmatingoccursaround
November–December.Lastly,highnumbersofalienI.iguanawouldpresumablycause
damagetoagriculturalfields,gardensandplantnurseriesasreportedelsewhere(foran
overviewseeFalcónetal.2013).
Fornaturalareas,over80%ofmangroveplantsinaPuertoRicanareawere
heavilyaffectedbyalienI.iguana(CarloandGarcía-Quijano2008).Asmangrovesare
globallythreatenedandindecline(Polidoroetal.2010),alsoinSingapore(Friessand
Webb2013)despitearecentminorrestoration(Laietal.2015),alienI.iguanaare
expectedtoaggravatethedeclineofSingapore’smangroves.RecordedI.iguana
presenceinSingapore’sSungeiBulohWetlandReserveisthereforeworrisome.Future
surveysandmonitoringarenecessarytobetterunderstandtheecologicalandeconomic
impactofI.iguanaestablishmentinSingaporeandThailand.
AstheglobalpettradehasfacilitatedthespreadofI.iguana,understanding
tradedynamicsmightaidthepredictionoffutureinvasions(Robinsonetal.2015;
Lockwoodetal.2019).AlthoughtheglobalI.iguanatradepeakedintheearly2000’s
(Stephenetal.2011),theimportofliveI.iguanatoAsiawashighestin2015andaclear
declineisabsent(Fig.A2,SupportingInformation).Weproposethatthisstabletrendis
partiallyduetolowershippingcostsandagrowingAsianmiddleclass(Kharas2017).In
additiontoourreport,sightingsofreleasedpetiguanashaveoccurredinTaiwansince
2004whereeradicationactionshavealreadyremoved>2,000I.iguanaindividuals(Lee
etal.2019).Similareradicationactions(plannedorongoing)ofpet-origininvasiveI.
iguanapopulationsareknownfromFijiandGrandCayman(Kraus2019;Rivera-Milán
andHaakonssoninpress).Combiningthesedata,wepredictthe(future)occurrenceof
additionalinvasivealienI.iguanapopulationswithinAsia,specificallyinthePhilippines,
giventheapparenthighoccurrenceofpetI.iguanasfromsocialmediaplatforms,high
numberofCITESimportrecords(Sy2015;CITES2019),aswellaslargeareaswithhigh
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habitatsuitability(Fig.A3,SupportingInformation).Lastly,therecordsofadultfree-
roamingiguanasfromPeninsularMalaysiaandHongKongarecauseforconcernaswell.
Futureassessmentsshouldidentifywhethertheseareisolatedcasesornot.
Assertiverapidactionisrequiredtohaltthespreadandtosuccessfullyremove
alienI.iguanapopulationsbeforetheybecomeinvasive.Tothatendweprovideseveral
recommendations.First,tomitigatecurrentandfuturenegativeeffectsoftheseI.iguana
invasions,werecommendtheimmediateimplementationofsurveyandquestionnaire
effortstobetterunderstandthespreadofthisspeciesinSingaporeandThailand.We
recommendbothdiurnalandnocturnalsurveyingwherediurnaleffortsmainlyaimto
locateadultandsub-adultspecimensandnocturnalsurveyshatchlingandjuvenile
specimens.Usinghigh-outputheadtorches(e.g.LedLenserH14r.2),small-sizediguanas
canbeeasilylocatedamongfoliagewheretheysleep.Secondly,andinparallel,we
recommendanoutreachcampaigntoraisepublicawareness,inform(future)pet
ownersofalltheconsequencescausedbyreleasingpetiguanasandpromotereporting
ofI.iguanasightingstotherelevant(local)authority.Also,informationshouldbe
providedtonewiguana-petownersuponpurchase,addressingtheincreaseinbody
size,longevity(19.8years[deMagalhãesandCosta2009]),overallexpensesand
necessaryspace.Tostrengthenthis,I.iguanaretailersshouldbeobligatedtoexhibitone
adultindividual(Maceda-Veigaetal.2019),andwerecommendthatretailersofexotic
petsareobligatedtohaveprovenknowledgeofthisspeciesandoftheirexhibition
standards.Thirdly,werecommendinspectionsofI.iguanacaptivitycircumstancesfor
allfacilitieswherethisspeciesiskept;forexample,zoos,recreationalparksandiguana
farms.Iguanasshouldnotbeallowedtoroamfreely,butinsteadbeexhibitedinlarge
cagesorsmall-sizedopenareasenclosedbyadeeptrenchwithasmoothmetallic
verticalsurfacetopreventclimbing;treebranchesfromwithintheexhibitionarea
shouldnotextendbeyondthistrench.Importantly,enclosureorentrapmentbywateris
ineffectivegiventheswimmingcapacityofI.iguana.Lastly,werecommendthat
releasingapetI.iguanabeimmediatelyprohibitedbylawinThailand,althoughdespite
itsprohibitioninSingaporethepracticecontinues(NgandLim2010).Petrelease
preventioncouldbeassistedbypittaggingallimportedandin-countrybrediguanasto
identifyregisteredowners.Besidestheabovementionedactions,additionalcountry
specificeffortsarenecessaryduringthisearlyestablishmentphaseinordertoprevent
futuremulti-milliondollareradicationefforts.
ConflictofInterest:Theauthorsdeclarethattheyhavenoconflictofinterest.
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DataAccessibility
TheRscriptanddatatorunSDMmodelsasmentionedinourMethodsandMaterials
areavailablethroughGitHub;github.com/StevenVB12/SDM_Iguana.
Acknowledgements
WearegratefultoallcontributorsforsharingdataonIguanaiguanasightings.Andwish
tothankJasonKolbeforimprovinganolderversionofthismanuscript.
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Supplementarymaterials
Fig.A1SpeciesdistributionmodelforIguanaiguanainSingapore,Thailandandsurroundingcountriesfor2050withtheACmodelandrcp45forgreenhousegasemission(FickandHijmans2017).Modelsusedanabsencethresholdof0.15andhabitatsuitabilityrangesfromhigh(darkred)tolow(white).BluedotsrepresentlocationswithI.iguanapresence.
19
Fig.A2ReportedCITESimportsofIguanaiguanatoAsiancountriesbetween2000–2017(CITESDatabase2019)
20
Fig.A3Speciesdistributionmodel(ashabitatsuitability)forIguanaiguanainPhilippinesundercurrentclimate,withabsencethreshold0.17.Habitatsuitabilityrangesfromhigh(darkred)tolow(white).
21
TableA1IguanaiguanasightingsinThailandandSingaporeincludinglocation,year,
numberofindividuals,andlifestage(s)present
Country Location GPS Year Individuals Life
stage(s)
Singapore SungeiTengahRoad 1.38075,
103.73031
2013,
2019
3 juvenile
andadult
Singapore JalanRengkam 1.36246,
103.88880
2014 1 subadult
Singapore JurongBirdPark,and
JurongHill
1.31950,
103.70503
2015,
2016,
2017,
2018,
2019
>20 all
Singapore BurgundyCrescent 1.34017,
103.76145
2015 1 subadult
Singapore SungeiPengSiang 1.3937,
103.7254
2016 2 adult
Singapore OldUpperThomson
Road
1.38030,
103.81884
2017 1 subadult
Singapore JapaneseGardens 1.33522,
103.73136
2018 2 adult
Singapore TanahMerah 1.32096,
103.96723
2018 1 juvenile
Singapore OldChuaChuKang 1.38,103.74 2018 2 adult
Singapore WarrenCountryClub 1.38500,
103.73411
2018,
2019
>10 juvenile
andadult
Singapore Temenggong
RoadMosque
1.2665,
103.8244
2018 1 adult
Singapore PasirRisPark 1.3794,
103.9503
2018 1 adult
Singapore JurongEcoGarden 1.35228,
103.69319
2018 1 adult
Singapore Serangoonarea 1.3554,
103.8632
2018 1 juvenile
Singapore BotanicGarden 1.31185, 2019 1 subadult
22
103.81609
Singapore YishunPond 1.42646,
103.84024
2019 1 adult
Singapore SengKangPcn 1.38602,
103.90940
2019 1 adult
Thailand KhaoYai
NationalPark
14.44932,
101.40164
2016 1 adult
Thailand NakhonRatchasima 14.85005,
102.07593
2016,
2017
7 adultand
juvenile
Thailand Sakaerat 14.48468,
101.92032
2017 1 adult
Thailand HuaHin 12.58,99.93 2018,
2019
3 adult
Thailand KaengKrachan
reservoir
12.91098,
99.61502
2019 1 adult
Thailand Korat 14.88712,
102.188312
2019 1 subadult
Thailand NakhonSi
Thammarath
8.4574,
99.9539
2019 >20 subadult
andadult
Thailand Ubonrat 16.77,102.71 2019 >30 subadult
andadult
Thailand Phattaya 12.86231,
100.96929
2019 6 adultand
juvenile
Thailand UthaiThanidistrict 15.42,99.74 2019 >20 adultand
hatchling
Thailand BanPongRatchaburi 13.81175,
99.86228
2019 5–20 adultand
hatchling
Thailand NattawutNambut 16.29974,
103.98282
2019 2 adult