Diversity and Distributions. 2019;00:1–14.  | 1wileyonlinelibrary.com/journal/ddi

Received:22June2019  |  Revised:9August2019  |  Accepted:12August2019DOI: 10.1111/ddi.12982

B I O D I V E R S I T Y R E S E A R C H

Topographic ruggedness and rainfall mediate geographic range contraction of a threatened marsupial predator

Harry A. Moore1 | Judy A. Dunlop2 | Leonie E. Valentine3 | John C. Z. Woinarski4 | Euan G. Ritchie5 | David M. Watson1 | Dale G. Nimmo1

ThisisanopenaccessarticleunderthetermsoftheCreativeCommonsAttributionLicense,whichpermitsuse,distributionandreproductioninanymedium,providedtheoriginalworkisproperlycited.©2019TheAuthors.Diversity and DistributionspublishedbyJohnWiley&SonsLtd.

1SchoolofEnvironmentalScience,InstituteforLand,WaterandSociety,CharlesSturtUniversity,Albury,NSW,Australia2ScienceandConservationDivision,DepartmentofBiodiversity,ConservationandAttractions,Kensington,WA,Australia3SchoolofBiologicalSciences,UniversityofWesternAustralia,Crawley,WA,Australia4ThreatenedSpeciesRecoveryHub,NationalEnvironmentalScienceProgram,CharlesDarwinUniversity,Darwin,NT,Australia5CentreforIntegrativeEcologyandSchoolofLifeandEnvironmentalSciences,DeakinUniversity,Burwood,VIC,Australia

CorrespondenceHarryA.Moore,SchoolofEnvironmentalScience,InstituteforLand,WaterandSociety,CharlesSturtUniversity,Albury,NSW2640,Australia.Email:harryamos@live.com.au

Funding informationInstituteofLand,WaterandSociety;FacultyofScienceatCharlesSturtUniversity;AustralianGovernment'sNationalEnvironmentalScienceProgram;ThreatenedSpeciesRecoveryHub;AustralianResearchCouncilEarlyCareerResearcherAward;WesternAustralianDepartmentofBiodiversity,ConservationandAttractions;BHP;RioTinto;AtlasIron;FortescueMetalsGroup;RoyHill;ProcessMineralsInternational;MetalsX;MainRoadsWesternAustralia

Editor:LucaSantini

AbstractAim: Speciesrangecontractionsareincreasinglycommonglobally.Thenichereduc‐tionhypothesispositsthatgeographicrangecontractionsareoftenpatternedacrossspaceowingtoheterogeneityinthreatimpactsandtolerance.Weappliedthenichereductionhypothesistothedeclineofathreatenedmarsupialpredatoracrossnorth‐ernAustralia,thenorthernquoll(Dasyurus hallucatus).Location: NorthernAustralia.Methods: Weassembledadatabasecontaining3,178historicandcontemporaryre‐cordsfornorthernquollsacrosstheextentoftheirdistributiondatingbetween1778and2019.Basedonthese records,weestimatedchanges in thegeographic rangeofthenorthernquollusingα‐hullsacrossfourmainpopulations.Wethenexaminedhowrangecontractionsrelatedtofactorslikelytomediatetheexposure,susceptibil‐ity,ortoleranceofnorthernquollstothreats.Result: Theextentofrangecontractionsshowedaneast–westgradient,mostlikelyreflectingthetimingofspreadofintroducedcanetoads(Rhinella marina). There were clearchangesinenvironmentalcharacteristicswithinthecontemporarycomparedtothehistoricgeographicrange,withthemostsubstantialoccurringinpopulationsthathavesufferedthegreatestrangecontractions.Thecontemporaryrangeiscomprisedofhigherqualityhabitats(measuredusingenvironmentalnichemodels),character‐izedbyhighertopographicalruggednessandannualrainfall,andreduceddistancetowater,comparedtothehistoricrange.Main conclusions: Changes to range andniche likely reflect the capacity of com‐plexhabitatstoamelioratethreats(namelypredationandalteredfireregimes),andaccesstoresourcesthat increasethreattolerance.Thisstudyhighlightsthemulti‐variate nature of ecological refuges and the importance of high‐quality habitatsforthepersistenceofspeciesexposedtomultiplethreats.Ourmethodsprovideausefulframeworkwhichcanbeappliedacrosstaxainprovidingvaluableinsighttomanagement.

K E Y W O R D S

introducedspecies,nichedecline,rangecontraction,refuge,threatenedspecies

2  |     MOORE Et al.

1  | INTRODUC TION

Thecontractionofspecies'geographicrangesistheresultofpopula‐tiondeclineandlocalextinction,andastark,prominentmanifestationofadverseanthropogenicenvironmentalchange(Hobbs,Valentine,Standish, & Jackson, 2017). Range contractions are increasinglycommon across the globe (Thomas, Franco, & Hill, 2006)—for in‐stance, 40%of 177mammal species studied byCeballos, Ehrlich,and Dirzo (2017) have experienced range contractions of >80%.As range contractions increase extinction risk (Purvis, Gittleman,Cowlishaw, & Mace, 2000), the extent of a species' geographicrange, aswell as its population size, are considered key elementsbytheInternationalUnionforConservationofNature(IUCN)inde‐terminingaspecies'globalconservationstatus(IUCN,2006).Rangecontractionsentrainaraftofchangesthatoccurwhenspeciesareindecline,suchaschangestospecies'niches(Breiner,Guisan,Nobis,&Bergamini,2017).Smallchangesinaspecies'geographicrangesizecancorrespond tosubstantial reductions in itsnichebreadth,andvice versa,duetolocalextinctionsoccurringindistinctenvironments(Breineretal.,2017),leadingtospatialpatterninginrangedeclines(McDonald,Luck,Dickman,Ward,&Crowther,2015).

Tointegratetheconceptsofrangedeclineandnichereduction,Scheele,Foster,Banks,andLindenmayer(2017)introducethe‘nichereductionhypothesis’.Thishypothesisdistinguishesbetweenaspe‐cies'‘historicalniche’—definedastherealizednicheofaspeciespriortodecline—andthe‘contemporaryniche’,asubsetofthehistoricalnicheafterareductioninnichebreadthduetonovelthreats(e.g.in‐troducedspecies,habitatloss,disease).Threefactorsthatshapethecontemporarynicheofspeciesare(a)threat occurrence,which,whenathreatoperatesvariablyacrossdifferentpopulationsorpartsofaspecies' range,maycausespeciestopersistonly inenvironmentalrefugia, (b)aspecies' threat tolerance, theability topersistdespite

threats,which can be increasedwithin a subset of environmentalconditionsdueto,forexample,largerpopulationssizes,and(c)geo‐graphic barriersthatexcludethreatsfromapartofaspeciesrange(Scheele et al., 2017). Understanding how threats shape species'niches,andgeographicranges, iscritical toconservation,as itcanassistinidentifyingecologicalrefuges(Resideetal.,2019).Further,basingconservationonthecontemporarynichecan leadtoanar‐rowunderstandingofa species'potentialhabitat, thereby limitingthe range of options available for conservation, translocation andrestoration(Scheeleetal.,2017).

Here,weapplyScheeleetal. (2017)niche reductionhypothe‐sisbyquantifyingchangesinthehistoricalandcontemporaryrangeandnicheof four populationsof amarsupial predator—thenorth‐ern quoll (Dasyurus hallucatus). The northern quoll is the smallestof fourDasyurus species found in Australia, ranging from 300 to1,200g,andmaleswithinthespeciesoftenexhibitasemelparouslife history, surviving for only a single breeding season (Oakwood&Cockburn,2001).ThegeographicrangeofnorthernquollsspansmuchofnorthernAustralia(Figure1),butissuspectedtohavede‐clinedconsiderablysinceEuropeancolonizationofAustralia(1788),andparticularlyinthepast50years(Braithwaite&Griffiths,1994).Consequently,thenorthernquollisclassifiedas‘endangered’bytheIUCN,with a ‘declining’ population trend (IUCN, 2016). Themainthreatstonorthernquollsarepredationbyintroducedanimalssuchas feralcats,poisoningbythe introducedcanetoads (Rhinella ma‐rina), and habitat degradation caused by altered fire regimes andgrazingbyintroducedherbivores(IUCN,2016).

Thenorthernquolloffersanexcellentcasestudyofrangecon‐tractionandnichereductioninadecliningspeciesforthreereasons.First,declines innorthernquoll rangehaveoccurred relatively re‐cently(i.e.fromthemidtolate20thcenturytothepresentday),andso,anextensivecatalogueofspeciesrecordsexistsfromwithinboth

F I G U R E 1  Northernquollpresencerecordsacrosseachofthefourpopulations.Bluemarkersrepresenthistoricpresencerecords,andmaroonmarkersrepresentcontemporarypresencerecords(>2,000).Populationsarerepresentedbyvaryinglinepatterns

     |  3MOORE Et al.

itshistoricandcontemporaryrange.This isnotthecaseformanyoftheAustralianmammalsthatdeclinedearlierfollowingEuropeancolonization(Woinarski,Burbidge,&Harrison,2015).

Second, in addition to range contractions, northern quolls arethought tohavesuffereda reduction innichebreadth,due to thedisproportionate lossof localpopulations fromparticularenviron‐ments, suchas lowland savannaand thearid fringeof their range(Braithwaite&Griffiths, 1994;McKenzie, 1981;Oakwood, 2000).Consistent with the niche reduction hypothesis, local extinctionsare thought to have related to both threat occurrence and threattolerance. For instance, topographically rugged areas (e.g. rockyoutcrops)areconsideredtoofferfixedrefuges(sensuResideetal.,2019)frompredation,grazingandfire(Burnett,1997),increasingthelikelihood of persistence of northern quolls (Begg, 1981). In addi‐tion,localextinctionsarehypothesizedtohaveoccurredmoreofteninmarginalhabitats(i.e.lowrainfallandlowerpopulationsize)thatpredisposepopulations to a lower threat tolerancedue to smallerpopulationsizes(Burnett,1997).

Third,rangecontractionsofnorthernquollslikelydifferacrossitsfourmainpopulations (Queensland,NorthernTerritory,KimberleyandPilbara),duetogeographicbarriersthathavesofarpreventedoneprimarythreat—thecanetoad(R. marina)—fromreachingpartsofthenorthernquoll'sgeographicrange.CanetoadswereintroducedtoQueenslandin1935andspreadwestwardsacrossthenorthernthirdofAustralia,reachingtheNorthernTerritoryduringtheearly1970s(Urban,Phillips,Skelly,&Shine,2008),andtheKimberleyin2010(Doodyetal.,2018;althoughtheyhavenotyetcolonizedthatregionentirely),buthavenotyetreachedthePilbara(AppendixS3).Theprimarymechanismbywhichnorthernquollsareimpactedbycane toads is through lethal ingestion (Shine, 2010).While therehave been a number of reports documenting local northern quollextinctions inQueensland (Burnett, 1997; Burnett & Zwar, 2009;Woinarski et al., 2008) and theNorthernTerritory (Braithwaite&Griffiths,1994;Oakwood,2004;Woinarskietal.,2010;Ziembicki,Woinarski,&Mackey,2013),fewerextirpationshavebeenrecordedin theKimberley (Hohnenet al., 2016;Start,Burbidge,McKenzie,& Palmer, 2007), and none have been documented in the Pilbara(Crameretal.,2016),apatternoflossconsistentwiththesequentialspreadoftoads.

Wequantifyandcompareenvironmentalconditionswithinthehistoricandcontemporarygeographic rangeof thenorthernquollacrossitsfourmajorpopulations,comparerangedeclineswithnichereductions (i.e. declines in niche volume), and compare environ‐mental conditionswithin the contemporary niche to thosewithinthehistoricniche.Wepredicted that rangesizeandnichevolumewouldbemostreducedinQueenslandandtheNorthernTerritory,duetotheirlong‐termexposuretocanetoads.Consistentwiththenichereductionhypothesis,wepredictedthatrangedeclineswithineachpopulationwouldrelatetoenvironmentalvariablesthatbuffer(duetoreducedco‐occurrence)or increasethethreattoleranceofquolls.Specifically,contemporaryrangeswouldtrendtowardsmoretopographicallyruggedareaswithhigherrainfallandgreaterprotec‐tionfromfirewhencomparedtohistoricrangesduetoextinctions

occurringmoreofteninmoreopen,topographicallysimpleandmar‐ginalhabitats.

2  | METHODS

2.1 | Study area

The region over which northern quolls are believed to have oc‐curredis~2,634,641km2andstretchesfromsouthofBrisbaneonAustralia'seastcoast,alongnorthernAustralia,tothePilbararegioninWesternAustralia.Thisregionincludesfourdiscretepopulationsofnorthernquolls: inQueensland, theNorthernTerritory (includ‐ing several islands), the Kimberley (including several islands) andthePilbara(Figure1).Weusedpreviousestimatesofnorthernquollrangetoguidetheplacementofpopulationboundaries(Braithwaite&Griffiths, 1994;Oakwood,Woinarski, & Burnett, 2016). Recentanalysis suggests each of these populations function as distinctevolutionally significantunits, and thus in the interestsof geneticconservation,theyshouldbeconsideredseparately(How,Spencer,&Schmitt,2009).

The Queensland population spans substantial climatic varia‐tionwithnorthernareascharacterizedbymonsoonalwetseasons(December–March),whilesoutherncoastalareasreceiverainfallthatislessseasonal,andthewesternextentexhibitssemi‐aridconditions(BOM,2019;Table1).Vegetationvariessignificantly ranging frommonsoonalrainforeststomixedeucalyptwoodlandsandtropicalsa‐vannas(NVIS,2019).TheNorthernTerritorypopulationexperiencesamonsoonaltropicalclimate,withrainfallfallingmainlyintheperiodDecember–March(BOM,2019;Table1).Vegetationismostlychar‐acterizedbyeucalyptopenwoodlandsand forests, spinifexgrass‐landsandtropicalsavannas(NVIS,2019).TheKimberleypopulationalsoexperiencesatropicalmonsoonalclimate(Table1).Vegetationis characterized by desert grasslands in the southern interior andtropicalsavannainthenorth(DPIRD,2017).ClimateinthePilbaraischaracterizedbyextremelyhotsummers,mildwintersandlowratesofsporadicrainfall (BOM,2019;Table1).Vegetation isdominatedby Acacia and Eucalyptus lowwoodlandsandhummockgrasslands(NVIS,2019).

2.2 | Data collection

Adatabasecontaining6,391northernquoll recordswascollectedfromnationalandstate/territoryfaunadatabases,museumrecords,past publications, trap records as well asmining and governmentagencies,datedbetween1788and January2019.Themajorityofrecords were sourced from online databases the Atlas of LivingAustralia (ALA,2019),NatureMap(NatureMap,2019)andWildnet(Wildnet,2019)aswellasa2008Australiangovernmentreportin‐vestigatingnorthernquolldeclineinnorthernAustralia(Woinarskietal.,2008).Duplicateswereidentifiedandremoved.Recordsmissinginformationorwithhigh locational inaccuracywerealsoremoved.Intheinterestofcontrollingforthreatabsencesonislands,allislandrecordswereremovedfromouranalysis.Tominimizetheeffectof

4  |     MOORE Et al.

localizedsurveyeffortonanalysis,all recordscollectedwithinthesameyearinthesame1km×1kmgridcellwerecondensedtoone.

FollowingMartínez‐Freiría,Tarroso,Rebelo,&Brito,2016),weseparatedourdatasetforeachpopulationintotwo:ahistoricaldataset,whichsoughttodescriberangespriortotheyear2001,andacontemporarydataset,whichsoughttodescribetherangeofpop‐ulations from2001onwards.Also followingMartínez‐Freiríaetal.(2016),thehistoricaldataset includedthecontemporaryobserva‐tions(i.e.was‘nested’),sothatitincludedallpopulationsthathavelikelybeenpresent(butmaynothavebeendetected)sinceEuropeancolonization.Thisapproachwasjustifiedgiventherelativelysparsesamplingeffortinthehistoricalperiod.Totesttheeffectthatnest‐ingcontemporaryrecordswithinhistoricrecordshadonourresults,we ran a series of analyses (methods below) on both nested andun‐nesteddatasetsandcomparedtheresults. InQueenslandandtheNorthernTerritory,wefoundnestinghadlittleimpactonrangecontraction,nichevolumeorhabitatsuitabilitypredictorimportance(AppendixS2).Conversely,intheKimberleyandthePilbara,wherehistoricalsamplingwaslessthorough,wefoundrangesizeandnichevolumeincreasedthroughtimeinun‐nesteddatasets—trendswithno supporting evidence.Basedon this comparison,we elected toonlyusenesteddatainfurtheranalysis.

Wechose theyear2000as theseparationpointbetweenhis‐toric and contemporary data sets as it allowedus to have a largenumberofpresencesbothbeforeandafterthispoint,facilitatingthedevelopmentofseparaterangeestimatesforeachpopulationduringeachofthetwotimeperiods(historicandcontemporary).Whilesep‐aratingthedataintomorethantwotimeperiodswouldhavebeenpreferable,theamountofpresenceswithinfinertemporalwindowsdidnotallowforthedevelopmentofreliablemodels.Further,whilewenotethatlocalextinctionshaveoccurredpost‐2000(Oakwood,2004), theseare likelyminorcompared to the reductions thatoc‐curredinthe20thcenturywhencanetoadsandinvasivepredatorsspreadacrossalargeproportionofthequoll'srange(Braithwaite&Griffiths,1994).

2.3 | Range contractions

Wemeasuredchangeingeographicrangeusingα‐hulls,astandardIUCN measure representing a generalization of convex polygonsthat accounts for breaks in a species range (IUCN,2006).Breineretal.(2017)foundα‐hullscloselytrackedsimulatedextinctionsandoutperformed a range of alternative range quantification metrics

(e.g. ENMs, convex polygons). Following IUCN recommendations(IUCN,2006),weusedanαvalueof twowhencalculatingα‐hullsforalldatasets.α‐hullswerecreatedusing ‘alphahull’packageinr (Pateiro‐López&Rodrıguez‐Casal,2009).

2.4 | Niche change

Wequantifiednichevolume (thespacedefinedwithintheboundsofn independentenvironmentalaxes) foreachpopulation ineachtimeperiod.Todothis,weusednichehypervolumesgeneratedbyaone‐classsupportvectormachinemethod(SVM),asdescribedbyBlonderetal.(2019).Hypervolumesweredefinedbytheboundsofthefiveenvironmentalvariables(Table2)andwerescaledpriortoanalysis (following Tingley, Vallinoto, Sequeira, & Kearney, 2014).TheSVMwasused as it is insensitive tooutliers and generates asmooth boundary around the data, yielding binary predictions ofnichevolume,facilitatingcomparisonsbetweendatasubsets.Onceall n‐dimensionalhypervolumeshadbeenassembled,nichevolumewascalculatedandcomparedwithinpopulationstoassessnichere‐duction.HypervolumeswerecalculatedintheRpackage‘hypervol‐ume’(Blonder,Lamanna,Violle,&Enquist,2014).

We created a layer of habitat quality for northern quollsacross study populations using ecological nichemodels (ENMs).Ecologicalnichemodelscombinepresencerecordswithenviron‐mentaldatatopredicthabitatthatismostlikelytosupportpop‐ulations of a given species (Guisan & Thuiller, 2005). Ecologicalnichemodelsweredevelopedusing theMaxEnt algorithm (Elithetal.,2011).MaxEntdefaultoutputconsistsofamapwitheverycell assigned a log value representing relative probability of oc‐currence,rangingfrom0to1.CellsizeforallENMsinthisstudywas1km2 (1 km×1km).Toquantifyhabitatqualitywithin therange of northern quolls, we incorporated five ecogeographicallayers based on evidence within the literature supporting theirrelevance to northern quoll ecology (Table 2). As presence‐onlydata are often subject to selection bias,we included a bias gridwithinMaxEntmodels, indicatingsamplebiasesacrossthestudyarea(Kramer‐Schadtetal.,2013).Weuseda‘targetgroup’back‐groundsamplingapproachtogeneratethebiaslayers(Phillipsetal.,2009).Wedefinedourtargetgroupasallcriticalweightrange(CWR)mammals (includingnorthernquoll)withinthestudyarea(followingMolloy,Davis,Dunlop,&vanEtten,2017).Thesespecieswereselectedassurveymethodsusedtodetectthemwouldalsodetectthenorthernquoll(followingMolloyetal.,2017)—typically

TA B L E 1  Studyareasizeandclimaticvariabilityintermsofmeancoldestandwarmestquartertemperature,aswellasannualprecipitation

Population Study area (km2)Mean coldest quarter temp range (°C)

Mean warmest quarter temp range (°C)

Annual precipitation range (mm)

Queensland 989,833 8.6–25.4 19.9–30.4 407–3,945

NorthernTerritory 619,058 17.9–24.3 28.2–31.6 340–1,834

Kimberley 362,014 19.1–25.6 27.6–33.0 419–1,453

Pilbara 663,736 13.2–21.9 28.6–33.3 216–465

     |  5MOORE Et al.

ahighlydetectablespecies(Austin,Tuft,Ramp,Cremona,&Webb,2017)—thusensuringbothnorthernquollpresencedataandmodelbackgrounddataweredrawnfromacomparablesamplinginten‐sity.Targetgroupspeciesrecordsweresubjectedtopointdensityanalysis (PDA),masked to a 1 km2 grid layer usingArcGIS 10.3,creatinga layerwithcellvaluesthataccuratelyrepresentsurveyeffortinrelationtolocation.ThislayerwasincludedasabiasgridinallMaxEntmodels.Thecontributionofvariablestoeachmodelwasassessedusingpermutation importancevalues.Permutationimportance is calculated by alternating the predictor values be‐tweenpresenceandbackgroundpointsandrecordingtheeffectthishasonmodelAUC(Phillips,2011).

Toquantifychangesintheenvironmentalconditionswithinthecontemporaryrangeofquolls,wesampledeachofourfiveenviron‐mental predictors 10,000 timeswithin historic and contemporaryα‐hulls,acrossallpopulations.Finally, toquantifychanges inhabi‐tatqualityovertime,wesampledtheMaxEnthabitatquality layerwithin both historic and contemporary α‐hulls.We used general‐izedlinearmodels(GLMs)tocomparetheaveragevaluesofthefiveenvironmentalpredictorsbetweenthetwotimeperiods,usingthehistoricperiodas the referencecategory.Weconsidered there tobesignificantdifferencebetweentimeperiodswhenthe95%con‐fidenceintervaloftheregressioncoefficientsdidnotoverlapzero.

Violinplotsweregeneratedtovisualizedthesedatausingthe‘plotly’ packageinr(Sievertetal.,2017).

3  | RESULTS

The totalhistoricdatabaseconsistedof2025historic recordsand1,153contemporaryrecords(AppendixS1).Rangesize,asestimatedby α‐hulls, declined across all populations except for the Pilbara.Consistentwithpredictions, the largest absoluteandproportionaldeclinesoccurred inQueensland (areal reductionof405,533km2,75.4% of the historic range), followed by the Northern Territory(115,024 km2, 57.7%) and the Kimberley (25,986 km2, 16.9%;Figure 2). Range declines in the Northern Territory were domi‐natedby the lossof recordoutliers fromthesemi‐aridgulf regionin the south‐east of their range. Total loss in range size across allpopulationswas546,886km2(45.2%;Figure2).InQueensland,thevastmajority of persisting northern quoll populations are presentontheCentralMackayCoastbioregion,thenorthernextentoftheNorthernBrigalowBelt,theWetTropicsregion(Cooktown,CairnsandAthertonTablelandsareas)andnearWeipaon theCapeYorkPeninsula (Figure 2). In theNorthern Territory, persisting popula‐tionsaremostlyfoundintheDarwinCoastalbioregion,thenorthern

TA B L E 2  Variablesincludedinnorthernquollecologicalnichemodelandhypervolumeanalysisaccompaniedbyjustificationforinclusionandsource

Variable Description Justification Source

Topographicalruggedness

Calculatedfromthedifferenceinelevationbetweenacellandtheeightcellssurroundingit(follow‐ingRiley,1999)

Studiessuggestqualitynorthernquollhabitatisoftenassociatedwithrockyruggedareas(Braithwaite&Griffiths,1994;Burnett,1997;Hernandez‐Satin,2016;Schmittetal.,1989)

CalculatedaccordingtoRiley(1999)GeoscienceAustralia(2018)

Elevation Metresaboveaveragesealevel Pollack1999foundnorthernquollsincentralQueenslandweretypicallyfoundatlowerelevation.Molloyetal.(2017)foundelevationwasastrongcontributortoMAXENTmodellingfornorthernquollsinthePilbara

GeoscienceAustralia(2018)

Annualprecipitation Derivedfromspatiallyinterpolatedmonthlyclimatedatabasebasedonaveragesbetween1950and2000

Increasedproductivityasaresultofhighannualprecipitationmayboostthecapacityofnorthernquollstotol‐eratethreats(Burnett,1997;Hohnenetal.,2016;McKenzieetal.,2007)

WorldClim(2019)

Precipitationseasonality Averagemonthlyvariationinrainfall(1950–2000)expressedasapercentageratioofthemeanmonthlyprecipitationtotalandthestandarddeviationofthemonthlyprecipitation

NorthernquollrecordsinQueenslandassociatedwithhigherlevelsofrainfallseasonality(Woinarskietal.,2008)

WorldClim(2019)

Distancetowater Distancetopermanentwatermeas‐uredindecimaldegrees

Studiessuggestareasproximatetopermanentwateraremorelikelytoprovidehighqualityfornorthernquolls(Begg,1981;Braithwaite&Griffiths,1994;Burnett,1997;Molloyetal.,2017)

Derivedfrom1:100,000water‐coursemappingprovidedbyGeoscienceAustralia(2018)

6  |     MOORE Et al.

extentofthePineCreekbioregion,andtheTiwiCobourgpeninsulaand the Victoria Bonaparte bioregion between the Victoria andFitzmaurice rivers.For theKimberley, contemporary recordsweremostlyfoundintheKingLeopoldRangesnorthofDerbyaswellastheMitchellPlateau region,particularlybetween theMitchell andLawley River National Parks. Northern quolls are still distributed

across the entire Pilbara bioregion and also enter the southernextentoftheGreatSandyDesertandwesternextentoftheLittleSandyDesertaroundKarlamilyiNationalPark.

Nichereduction,measuredashypervolumes,occurreddifferen‐tiallyacrossallpopulations,closelymatchingrangedeclines intheNorthern Territory (60.8%) and the Kimberley (16.9%). Marginal

F I G U R E 2  Northernquollhistoricandcontemporarypredictedrangeacrossfourstudypopulationsusingα‐hulls.ColouringwithinrangesrepresentsoutputsfromMaxEntecologicalnichemodels.Valuesintheright‐handcornerofplotsrepresentsα‐hull area

0 km 500 km 1000 km 0 km 500 km 1000 km

250 km 500 km0 km 250 km 500 km0 km

150 km 300 km0 km 150 km 300 km0 km

200 km0 km 0 km 200 km

538,080 km2 132,547 km2

199,514 km2 84,490 km2

153,824 km2 127,838 km2

319,692 km2 319,350 km2

1.0

0.5

0.0

0.25

0.75

     |  7MOORE Et al.

declinesoccurred inthePilbara (0.1%).Whilesubstantialnichere‐ductionwasalsoobservedinQueensland(49.2%),itwasapropor‐tionallysmallerreductioncomparedtorangedeclines(Figure3).

TheperformanceofMaxEntmodelswashighacrosseachofthefourdatasets,withAUCvaluesaveraging0.92(SD0.02;AppendixS2).Littlechangewasobservedinvariablepermutationimportancebetweentimeperiods,exceptfordistancetowaterintheNorthernTerritory,whichincreasedby22percentagepointsbetweenhistoricandcontemporaryperiods(Figure4).Annualprecipitationwasthemostimportantpredictorin6ofthe8ENMs.Precipitationseasonal‐ityalsocontributedhighlyinQueensland(Figure4).

Therewerecleardifferencesbetweentimeperiodsintheaver‐agevaluesofenvironmentalvariableswithinthegeographicrangesofallfourpopulations(Figure5),andinhabitatqualityasmeasuredbyMaxEnt,asindicatedby95%confidenceintervalsofcoefficientsnot overlapping zero (Figure 5). The largest changes occurred inQueensland and the Northern Territory, and smaller changes oc‐curredintheKimberleyandthePilbara(Figure6).Consistentwithpredictions,valuesfortopographicruggednessandannualprecipi‐tationincreasedinthecontemporaryrangecomparedtothehistoricrange inQueensland,theNorthernTerritoryandtheKimberley.AlargepositiveshiftinprecipitationseasonalitywasalsorecordedforQueensland.Finally,consistentwithpredictions,habitatquality(asmeasuredbythehistoricMaxEntmodel)washigherinthecontem‐poraryrange,suggestingalossoflowerqualityhabitats(Figures5and6).

4  | DISCUSSION

Weappliedthenichereductionhypothesis(Scheeleetal.,2017)toquantifychangesinthegeographicrangeandecologicalnicheofade‐cliningmarsupialpredatorthroughtime,acrossmultiplepopulations.Ourresultsconfirmacontractioningeographicrangeandnichevol‐umefornorthernquollsinQueensland,theNorthernTerritoryandtheKimberley(Braithwaite&Griffiths,1994;Woinarskietal.,2008).Aspredicted,rangedeclineshavebeenmostsevereinQueensland

andtheNorthernTerritory, lesssevere intheKimberley,andneg‐ligible in the Pilbara. These findings are consistent with localizeddeclines in each of these regions (Braithwaite & Griffiths, 1994;Burnett,1997;McKenzie,1981)andatleastpartlyreflecttheincre‐mentalspreadoftoxiccanetoadsacrossthespecies'range(Urbanetal.,2008).Reductionsinthenorthernquoll'snichevolumewere>20%inallpopulationsotherthanthePilbara,and,consistentwiththenichereductionhypothesis,wefoundevidenceofenvironmen‐talvariablesmediatingnichereduction,potentiallyduetothreatoc‐currence,species'tolerancesandgeographicbarriers.

Niche volume—the array of environmental conditionswithin aspecies'realizedniche—isapredictorofextinctionriskbothnowandovergeologicaltime‐scales(Saupeetal.,2015).Reductionsinnichevolumewerelargelyproportionatetorangecontractions,exceptinQueensland,where proportional range declines exceeded propor‐tionalreductionsinnichevolume.Thisresultalignswiththeorysug‐gestingspeciesrangeandnicheshouldbecorrelatedforthemostpart(Slatyer,Hirst,&Sexton,2013);forexample,arecentanalysisof148speciesusingsimulateddatafoundnichevolumeandrangesizeweremostlysimilar,althoughconsiderableresidualvariationdidexist(Breineretal.,2017).Thisvariationwasalsodetectedinouranalysiswithrangedeclineexceedingnichedeclineby29%inQueensland,reaffirmingthatwhileaconsistentrelationshipbetweennichevol‐umeandrangesizeholdsforthemostpart,oneisnotalwaysfullyreciprocaloftheother(Colwell&Rangel,2009).NichemayprovideapoorsurrogateforrangeinQueenslandgivenquollshavedeclinedfrom large swathes of flatter, more open (and relatively homoge‐nous)country,characterizedbyopensavannawoodlandvegetationandacaciaforests,similartodeclinesfromgrasslandsandsavannahabitatobservedintheNorthernTerritory(Oakwood,2000).Whilelessdiverseintermsoftopographyandvegetationthancoastalhab‐itats,thishabitataccountedforthemajorityofQueenslandnorthernquollhistoricrange,andthusindisappearingfromtheseareas,rangesizewasreducedtoalargerextentthannichevolume.

Our finding that the Pilbara population has experienced lessrange contraction andniche reduction compared toother regionsis consistentwithexpertopinionand the literature—thePilbara isgenerallyregardedasastrongholdforthenorthernquoll,duelargelytothe(current)absenceofcanetoadsandabundanceoftopograph‐ically complex rocky outcrops (Cramer et al., 2016).However,werecognize that a smaller range contraction in thePilbaramayalsobeanartefactoflowhistoricrecordavailability.Ourfinaldatabaseforthisregioncontained66uniquenorthernquollrecordscollectedbefore2001,and740uniquerecordsfrom2001onward—an11‐foldincrease.Thedifferenceinsamplesizeisduetoamassiveincreaseinsurveyeffortaspartofimpactassessmentsandoffsetsrelatedtoaboominironoreexplorationbetween2002and2015(ABS,2018).However,ourfindingsaresupportedtosomeextentbygeneticdatafromthePilbara,whichshowsnosignsofsubstantialrangecontrac‐tion(Spenceretal.,2013).

By comparing the average values of environmental variablesthatshapenorthernquolldistributionswithinthehistoricandcon‐temporaryniches,weassessedaseriesofhypothesesregardingthe

F I G U R E 3  Changeinnorthernquollrange(α‐hull),andnichevolume(hypervolume)plottedagainstoneanother.Queensland(purple),NorthernTerritory(blue),Kimberley(green),Pilbara(red).Thesolidlineshowswherea1:1correspondencebetweenrangedeclineandnichedeclinewouldfall

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typesofenvironmentsthatwouldfavournorthernquollpersistence.We found that the contemporarynichequolls is characterizedbymoretopographicallyruggedareas,supportingthehypothesisthatcomplex landscapes increase the resistance of northern quolls tothreats(orbecauseinsuchareasthethreatsareabsentoroflowerintensity)byactingasfixedrefuges(Resideetal.,2019).WefoundsupportforthishypothesisinallpopulationsotherthanthePilbara,withthegreatestincreaseobservedintheQueenslandpopulation.The increase in ruggednesswithin theQueensland contemporaryrangelikelyreflectsthelossofpopulationsthatpreviouslyoccupiedhighly flammable, topographically simple landscapes, thought tohavebeenmoreexposedtothethreatsoflivestockgrazing,alteredfire regimes (more frequentand intense fires)and invasivepreda‐tors (Hernandez‐Satin, 2016; Oakwood, 2000). Similarly, centralrockrats(Zyzomys pedunculatus)havecontractedfrommoresimpletomorecomplexruggedhabitatwheretheimpactoftheirprimarythreat, the feral cat, is reduced (McDonald, Stewart, & Dickman,2018). Rocky habitats are also important to northern quolls be‐causetheyprovidehighlysuitableareaswithinwhichfemalesareabletoestablishmaternaldenningsites (Oakwood,1997)—criticalfeatures in providing developing offspring with protection frompredators (Oakwood, 2000). The importance of suitable denninghabitat is further compounded when considering the unusually

short, semelparous life history of northern quolls, which makespopulation persistence particularly reliant on recruitment (Moro,Dunlop, &Williams, 2019), and thus the effectiveness of dens inproviding youngwith protection.While there is no evidence thatrugged habitats reduce the direct impacts of cane toads, it hasbeen suggested that, by limiting the impacts of grazing, fire andinvasive predators, rocky habitats may indirectly buffer againsttoadsby increasingpopulationsizes thatcanoffsetmortalitydueto toads (Burnett, 1997). And then this finding is consistentwithprevious work showing that northern quolls are found at higherdensities and that individuals live longer, in rocky habitats (Begg,1981;Schmittetal.,1989).Asimilarmechanismmightexplainwhynorthernquollcontemporaryrangeischaracterizedbyadecreasingdistancetopermanentwaterwhencomparedtothehistoricrange,asnorthernquollshavebeen found inbetter reproductivecondi‐tion closer to creek lines—ahabitat associatedwith free‐standingwater(Braithwaite&Griffiths,1994).Theauthorsofthatstudysug‐gestquolls closer towater are likely toengage in increased ratesofreproduction,presumablybecauseofanincreasedavailabilityofresources,leadingtoincreasedrecruitmentandoverallpopulationsize (Braithwaite&Griffiths,1994).This finding is also consistentwithResideetal.(2019),whoidentifiedwatersourcesasimportantfixedrefugesforthreatenedspecies.

F I G U R E 4  PermutationimportanceofvariablesincludedinnorthernquollMAXENTecologicalnichemodels.PermutationimportanceiscalculatedbyalternatingthepredictorvaluesbetweenpresenceandbackgroundpointsandrecordingtheeffectthishasonmodelAUC

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Someof the largest changes inenvironmental valuesbetweenthehistoricandcontemporarynichewereforannualrainfall,whichwasalso themost importantvariabledrivingquolldistributions inthreeofthefourregions.Thecontemporarynicheischaracterizedby much higher average annual rainfall compared to the historicniche, particularly in the two regions that have experienced thegreatest range declines (Queensland and the Northern Territory).Themost likely explanation for this shift is that rainfall increasesprimaryproductivity (Pianka,2017),andfoodresources (Dickman,Mahon,Masters,&Gibson,1999),leadingtoimprovedbodycondi‐tion,increasedoffspringsurvivorshipandpopulationsize(Meserve,Gutiérrez, Yunger, Contreras, & Jaksic, 1996), thereby offsettingincreasedmortality due to threats. Support for this hypothesis innorthern Australia is strong, with native mammals typically per‐sisting longer inareasthat receivehigherannual rainfall (Fisheretal.,2014;Start,Burbidge,McDowell,&McKenzie,2012).Northernquollsalsopersistmoreinhigherrainfallareas(Radfordetal.,2014;Woinarskietal.,2008;Ziembickietal.,2013),eventhoughthreatssuchasgrazing,predationandintensefirearepresentacrossboththearidandmesicextentsoftheirrange.Hohnenetal.(2016)sug‐gestedonereasonnorthernquollpopulationsmaybemorestableinhighrainfallareasisbecausegeneticconnectivityisgreater.Theysupported this hypothesis by showing quolls in wetter habitatsweremorecloselyrelatedthanquolls indrierhabitats (Hohnenetal.,2016).Here,itisimportanttonotethatouranalysisdidnotac‐countforchangesinrainfallpatternsovertime,afactorwhichhas

thepotentialtodriveshifts inspeciesrange(Davis&Shaw,2001)andniche (Broennimannet al., 2007).While the inclusionof suchanalysiswasoutsidethescopeofthisstudy,westronglysuggestthistopicbeaddressedinfuturestudiesasithasbeeninotherspeciesofquoll(Fancourtetal.,2015),particularlyinthecontextoftheearth'srapidlychangingclimate(Urban,2015).

WealsoobservedasubstantialincreaseinrainfallseasonalitywithinthecontemporarynicheinQueensland.Aswiththeprevi‐oustwoexamples,wesuggestthatthisshiftmost likelyreflectsincreasedpopulationsizeandoutputrelatedtothetiminginquollbreedingactivity,whereoffspringdispersal(November–February;Oakwood, 2000) coincides with a boom in resource availabilitybrought by summer monsoonal systems in northern Australia(Oakwood, 2000). By synchronizing their reproductive time linewith highly seasonal rainfall patterns, northern quolls are likelyabletoincreaseoffspringsurvivorship,allowingpopulationstobemore likely topersistdespite increasedmortalitydue to threats(e.g.canetoads,invasivepredators).

By comparing habitat quality derived from MaxEnt modelswithin the historic and contemporary niche, we found that thecontemporary geographic range of northern quolls comprises asubset of the historical niche that is of higher predicted habitatquality, highlighting the importance of high‐quality habitats forprovidingrefugefromstressors.Here,itisimportanttorecognizethatrefuges,likeniches(Guisan&Thuiller,2005),aremultivariateandcanbedefinedbytheboundsofmorethanoneenvironmental

F I G U R E 5  Violinplotscomparing10,000randomsamplesofhabitatvariableswithinthehistoric(blue)andcontemporary(maroon)rangeofnorthernquolls:(a)annualprecipitation,(b)precipitationseasonality,(c)elevation,(d)distancetowater,(e)topographicalruggednessand(f)habitatqualityderivedfromtheMaxEntmodel

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parameter(Keppeletal.,2012).Themosteffectiverefugesshouldoccurontheenvironmentalcontinuumwhereresourceavailabil‐ityandbufferingfromthreatspermitthegreatestchanceofper‐sistence (Keppel et al., 2012). In Queensland and the NorthernTerritory,whereshiftstohigh‐qualityhabitatweregreatest,hab‐itat qualitywas best predicted by annual precipitation, distancetowaterandprecipitationseasonality.ThisresultconformswithresearchshowingmammalattritioninAustraliahasbeengreatestin resource‐poor arid and semi‐arid landscapes (Johnson,2006).Topographical ruggedness was also an important predictor forhabitat quality in Queensland and the Kimberley, suggesting acombinationofcomplexandhigh‐resourcehabitatsmay insomecasesactasmoreeffectiverefugehabitatthanhabitatthatissim‐plyhighinresources.

While effective refuge habitat is clearly critical to the per‐sistenceofspeciesintheshortterm,itcanalsobeimportantatanevolutionaryscaleasrefugium—aspacewithinaspeciesnichethatcansupportpopulationsoverevolutionarytime‐scales(Keppeletal., 2012;Resideet al., 2019). In the caseof thenorthernquoll,

habitatthatlimitsbutnotfullyeliminatesexposuretokeythreatssuch as cane toads and feral predators may facilitate the de‐velopment of both behavioural and phenotypic traits throughbehavioural learningorevolutionthatcouldpotentiallyallowre‐expansion into their historic niche. Previous studies have foundthetimeframeforsuchchangestooccurinresponsetothreats(in‐cludingcanetoads)canbesurprisinglyshort(<70years;Hudgens&Garcelon,2011;Phillips&Shine,2006).Further,recentstudieshavefoundthatnotonlycannorthernquollsbetrainedtoavoidcanetoadsinasinglegeneration,butthatthetrainedquollsoff‐spring also avoided eating toads, suggesting quolls have the ca‐pacity to rapidly learn behaviour and distribute the informationto their young (Cremona, Spencer, Shine,&Webb, 2017;Webb,Legge,Tuft,Cremona,&Austin,2015).Theseresultssuggest in‐vestmentinprotectingrefuges(andpopulationswithinthem)overarelativelyshortperiodoftimehasthepotentialtoyieldimport‐antconservationoutcomes.

Animportantcaveatofourstudywasthatwedidnotexplicitlyaccountforthreatssuchascanetoads,feralpredatorsorfire,inanyofourmodels.Whileincludingthreatsaspredictorswouldlikelyaidindeterminationoftheirrelativeinfluenceinshapingthenorthernquoll's contemporary rangeandniche, the scale and resolutionofspatial layers required for this analysis do not currently exist andcreatingthemwasbeyondthescopeofourstudy.Itmaybepossibletoexplicitlytesttheeffectofthreatsonquollpopulationsinfuturestudiesbylimitingthescaleofanalysistoaregionallevelandlink‐ing changes in northern quoll occupancywith threat distributions(Hernandez‐Satin, 2016). For example, by measuring declines inrangeandnicheinrelationtofire,itmaybepossibletoelucidatethevalueoflogsandtreehollows—importantrefugefeaturesformanynorthernborealandarborealmammalspecies(Goldingay,2012)—asquollhabitat.

4.1 | Management implications

Previousresearchsuggestscanetoadshaveimmediateandlastingdetrimentalimpactsonnorthernquollpopulations(Shine,2010).Itis therefore likelythatcanetoadsareakeyculprit responsibleforlargerrangeandnichecontractionsinQueenslandandtheNorthernTerritory (Burnett, 1997;Woinarski et al., 2008), given that canetoadshaveonlyveryrecentlyarrivedinWesternAustraliaandareyettoreachthePilbara(Pizzatto,Both,Brown,&Shine,2017).Canetoads are expected to colonize the remainder of the Kimberleywithinthenext5–10years(Doodyetal.,2018)andthePilbaraby2037–2046(Southwell,Tingley,Bode,Nicholson,&Phillips,2017).Inthelightofthesepredictions,severalstrategieshavebeendevel‐opedtohaltorslowthespreadofcanetoadsfromtheKimberleytothePilbara(Phillips,Shine,&Tingley,2016;Tingleyetal.,2013).Theseincludeclosingoffwaterbodies(Tingleyetal.,2013),aswellasintroducingtoadswith‘lessdispersive’genestothefrontoftheinvasionlinetoimpedetheprogressoftoadscarrying‘highlydisper‐sive’ genes (Phillips, 2016;Phillips et al., 2016).We suggest thesestrategiesbegivenfullconsideration.

F I G U R E 6  Generalizedlinearmodelcoefficientscomparing10,000randomsamplesofhabitatvariablesfromwithinthehistoricandcontemporaryrangesofnorthernquolls:(a)annualprecipitation,(b)precipitationseasonality,(c)elevation,(d)distancetowater,(e)topographicalruggednessand(f)habitatqualityderivedfromthehistoricalMaxEntmodel.Positivecoefficientsdepictanincreaseinaveragevaluesofthevariableinthecontemporary(cfhistoric)range.Negativecoefficientsdepictadecreaseinaveragevaluesofthevariableinthecontemporary(cfhistoric)range

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Aswiththenorthernquoll,previousstudiesshowtopograph‐icallyruggedandhighrainfallhabitatsalsoprovideimportantref‐ugeforarangeofotherthreatenedspeciesofmammal(Southgate,Paltridge,Masters,&Carthew,2007)andassuchshouldformareasoffocusformanagement(Resideetal.,2019).Afirststepinprotect‐ingrefugehabitatsisrecognizingwheretheyarelocated,aprocessthathasbeenenhancedbyremotesensingtechnologies (Allanetal.,2018).Oncearefugeislocated,amanagementpriorityshouldbetoameliorateanyexistingoremergingstressorstoensuretheyremainfunctional infacilitatingspeciespersistence (Resideetal.,2019).Inthecaseofnorthernquolls,thesemayincludelimitingex‐tensivegrazingandburning,aswellasimplementingferalpredatorcontrolprogrammes(Hill&Ward,2010),andpotentiallyapplyingcanetoadaversiontechniques(O'Donnell,Webb,&Shine,2010).Althoughweexcludedislandsfromconsiderationsinouranalyses,themarkedcontractionsinrangeandnicheformainlandquollsre‐inforcetheimportanceofislandpopulationsandtheneedtomain‐tainbiosecurityfortheseislandstoreducethelikelihoodoftoadorpredatorinvasion.Finally,effectivemanagementofrefugesystemsrequires high‐quality ecological data collected over biologicallymeaningfultimeframes (Lindenmayeretal.,2012).Therefore, theimplementationofsustainedandeffectivemonitoringprogrammesinsideandoutsiderefugehabitatsishighlyrecommended.

ACKNOWLEDG EMENTS

WethankallwhocontributedtorecorddatabasesthatwereusedinthisstudyaswellasauthorsofWoinarskietal.(2008)forcollatingmanyoftheQueenslandrecords.WealsothankDeannaDuffy,RachelWhitsedandSimonMcdonaldfortheirassistancewithmanipulatingspatialdata,andDebraNoy for assistencewith administration.H.A.M.was sup‐portedbyascholarshipfromtheInstituteofLand,WaterandSociety,operatingfundsfromtheFacultyofScienceatCharlesSturtUniversityandlabspacefromtheEcosystemRestorationandInterventionEcologyGroupandtheUniversityofWesternAustralia.L.E.V.wasfundedbytheAustralianGovernment'sNationalEnvironmentalScienceProgramthrough the Threatened Species Recovery Hub. D.G.N. was sup‐ported by an Australian Research Council Early Career ResearcherAward(DECRA).ThisprojectwassupportedbytheWesternAustralianDepartmentofBiodiversity,ConservationandAttractionsaswellasenvironmentaloffsetsandpublicgoodfundingprovidedbyBHP,RioTinto,AtlasIron,FortescueMetalsGroup,RoyHill,ProcessMineralsInternational,MetalsXandMainRoadsWesternAustralia.

DATA AVAIL ABILIT Y S TATEMENT

StudydataarepubliclyavailableviadatasharingplatformDryad.

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BIOSKE TCH

Harry Moore is aPhDstudent interested inhowpredators in‐teractwithbioticandabiotic factorswithin theirenvironment,and how these shape their spatial ecology and behaviour. Theresearchersinvolvedinthispublicationhavebroadexpertiseinmammal conservation, applied ecology, field ecology and eco‐logicalmodelling.

Author contributions: H.A.M. andD.G.N. conceived the ideas;H.A.M.collectedthedata;H.A.M.andD.G.N.analysedthedatawithinputfromJ.A.D.andJ.C.Z.W.;andH.A.M.andD.G.N.ledthewritingwithinputfromJ.C.Z.W.,J.A.D.,E.G.R.,D.M.W.andL.E.V.

SUPPORTING INFORMATION

Additional supporting information may be found online in theSupportingInformationsectionattheendofthearticle.

How to cite this article:MooreHA,DunlopJA,ValentineLE,etal.Topographicruggednessandrainfallmediategeographicrangecontractionofathreatenedmarsupialpredator.Divers Distrib. 2019;00:1–14. https://doi.org/10.1111/ddi.12982