lynx habitat use - cpw.state.co.us...of habitat was below 0.102 units per ha (~1 unit per 10 ha)....

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Areasofhighhabitatusefrom1999‐2010forradio‐collaredCanadalynxreintroducedtoColorado

DavidM.Theobald,PhD.DepartmentofFish,Wildlife,andConservationBiology

ColoradoStateUniversityFortCollins,CO80523‐1474

andTanyaM.Shenk*

ColoradoDivisionofWildlife,MammalsResearchFortCollins,CO80526

31March2011*currentaffiliationNationalParkService,BiologicalResourcesManagementDivision,FortCollins,CO80525

IntroductionThepurposeofthisreportistodescribeananalysisofcurrenthabitatuseforthe

218CanadalynxthatwerereintroducedtoColoradofrom1999to2006.Theprimarydatasetusedhereislocationdatafromcollaredindividuals,andcollectedbytheColoradoDivisionofWildlifefrom1999untilpresent.Datafromindividualanimalswerecombinedtogethertoforma“population‐level”estimateofhabitatusebyweightinglocationsbasedonthenumberofmonthsdatawerecollectedforanindividual.Basicdescriptiveandsummarystatisticssuchasacumulativedistributionfunctionproviderelativeproportionofuseinagivenclassofhabitat.Notethatthisstudywasnotintendedtoexamineindividualhomerangesize,territoriality,ormovementrelativetolanduseand/ortransportationcorridors,norisitintendedtopredictpotentialorfuturehabitatuse.

Methods

PreparationoflocationdatasetIreceivedtwodatasetsonlynxlocationsfromCDOW(TanyaShenkandJakeIvan,

personalcommunication)datedNovember9,2010.TheVHFdatasetwascollectedbylocatingindividuallynxviatelemetryduringfixed‐wingairplaneflights.MostofthelocationsweresouthofI‐70,asmonitoringwasfocusedonobservinganimalsinthecorereleasearea,roughlydefinedasthehighelevationareasinsouthwesternColoradoboundedbyTaylorMesaonthewest,Gunnisonbasinonthenorth,PonchaPassontheeast,andNewMexicoborderonthesouth.Aeriallocationswereobtainedoutsideofthecoreareaonanopportunisticbasis,typicallyonly1locationper3months.TheentireVHFdatasethad11,356observationsfor257individuals(103females,117males)collectedfrom2/4/1999to6/22/2010.

TheArgosdatawerecollectedfromlynxthatwereoutfittedwithdualVHF/Argossatellitecollars,beginninginApril2000.Thesecollarsweredesignedtoprovidelocations

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onceperweek.TheArgosdatasethad33,778observationsfor196individuals(97females,88males),collectedfrom3/1/2000to8/11/2010.

Basedonanumberofdiscussionswithlynxbiologistsandstatisticians1,wefilteredthedatasetsinthefollowingways:

a. Removethefirst6monthsoflocationsafterreleaseforeachindividualtoreducelikelybiasof“justreleased”movements.Thisresultedin35,276locationsdatingfrom9/13/1999to8/11/2010,representing198individuals(152with>30locations).

b. RemoveArgoslocationswithhighspatialuncertainty(Table1;LocationClass1,0,A,B,Z)andretaintherest(LocationClass3and2).Thisresultedin15,545locationsrepresenting197individuals(129with>30locations).

c. Removelocationsthatrepresentmultiplefixesinaday,retainingthemostpreciselocationestimate(VHF,Argos3,Argos2).Thisresultedin13,803locationsrepresenting197individuals(118with>30locations).

d. Removerecordsforindividualswithlessthan30locations,resultingin12,796locationsfrom118individuals

Thus,thefinaldatasetusedintheanalysisincluded12,796observationsfor118individuals(Figures1&2;numberofindividuals:f=64,m=54;totalmonthsofdata:f=2679,m=1784).NotethatIdidnotconductananalysisthatseparatessummerfromwinteruse,ormalesfromfemales.Figure3showsthedistributionoflynxlocationsbyyear.Table1.Spatialuncertaintyofthelocationdata.*indicatesdatatypesusedintheanalysis.

Locationsource/class

Description Radius(m)encompassing68%oferrordistribution

Radius(m)encompassing95%oferrordistribution

*VHF Datacollectedbytelemetry 200 400*Argos3 <250m 250 500*Argos2 250‐500m 375 750Argos1 1500m 1500 3000Argos0 N/A Notused ArgosA,B,Z N/A Notused

1WithTanyaShenk(NPS)andJakeIvan,PaulLukacs,andMindyRice(CDOW)

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Figure1.Thenumberofobservationsandmonthsfor118individuallynxusedintheanalysisofhabitatuse.

Figure2.Thedistributionof118individuallynxusedintheanalysisofhabitatuse.Differentcolorsdenotedifferentindividuals.

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Figure3.Thedistributionoflynxlocationsusedinthisanalysis,displayedbyyearfrom1999to2010.

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GenerateutilizationdistributionsIfollowedthegeneralapproachofMillspaughetal.(2006)topreparetheutilization

distributionsurfaceandexplanatoryvariables.First,Iestimatedtheutilizationdistribution(UD)foreachindividualanimalusinga

homerangeestimatorcalledlocalconvexhulls(LoCoH;GetzandWilmers2004).Weselectedthisapproachbecauseitisnon‐parametric,producesaUD,andidentifiesabrupt“edges”inthespatialdistributionthatcanoccurbecauseofedgesinlandscapefeatures(e.g.,topographicconstraints)orterritorialityamongindividuals.Generally,LoCoHextendstheconceptofconvexhullstodelineatespaceuse,butratherthanencompassingallpointsatonce(e.g.,minimumconvexpolygon),itworksonasub‐setofpointstoidentifylocalconvexhulls.Thatis,asmallor“local”convexhullisidentifiedaroundpointi,whichcontainsasetofknearestneighbors.Thelocalhullsarethensortedbyarea,smallesttolargest,andtheUDvalue(orisopleths)aredeterminedbytheproportionofpointsfoundineachlocalhull.

Specifically,weusedtheadaptiveversioncalleda‐LoCoHbecauseitismostinsensitivetosub‐optimalvalueparameterization(Getzetal.2007).a‐LoCoHidentifiesavariablenumberofknearestneighborssuchthatitusesallpointswithinavariablecirclearoundarootpointsothatthesumofdistancebetweenthepointsandtherootpointdoesnotexceedauser‐definedthresholdvalue,a.Thismethodadjuststheradiussothatsmallerconvexhullsariseinhighuseareasandprovidemoreclearlydefinedisoplethsinregionswithhigherdensityoflocationdata.Getzetal.(2007)recommendedsettingatothemaximumdistancebetweenlocationpoints(withaminimumofk=3),whennootheraprioriinformationisavailable.Iusedtheaverageofthewidthandheightofthemaximumenclosingconvexhullbecausehabitatuseoftenoccurredindisjunctclusters.ToremoveartifactsintheLoCoHoutputthatcanbeintroducedbyspuriouslocationvalues,Iremovedthe100%isopleth(leavingallisopleths<=90%).EachUDwasnormalizedsothattheareaundertheUDsummedto1.0.

Second,tocombinetheUDsforthe118individualsintoageneral,population‐levelestimateofhabitatuse,Icomputedthenumberofmonthsoflocationdataforeachindividual.Thisprovidedaweightsuchthatindividualswhohadarelativelyshortdurationoflocationswouldhaveminorinfluence,whileanindividualwithalongduration(manymonths)oflocationdataavailablewouldhavemoreinfluenceonthepopulation‐levelUDsurface.Theweightsrangedfrom11to113,withameanof37.82(SD=18.49).Foreachcellwithinanindividual,normalizedUDvaluesweremultipliedbytheappropriateweightandtheresultwassummedateachrastercellacrossallindividuals.2Thus,ifonecellorgeneralareaisusedintenselybyonlyoneindividual,itwillbehighintensityuse.Conversely,ifnumerousindividualshaveusedalocation,eachatalowerintensity,ittoo,willhaveahighUD.

Third,IsmoothedtheUDvaluesfromaresolutionof90mtoamorebiologically‐basedresolutionthatwasequaltotheareaofthesmallestobserved“highuse”UDobservedacrossallindividuals–225.0ha.Iaggregatedthe90mcellstoacellsizeof1440m(~207ha).3Thisprovides11,934cells(at1,440m)inthepopulation‐levelUD(pUD).2Multipliedby100,000,000anddividedbytotaltogetintegergrid,from1‐1701.3Aggregatedbasedonthesmallesthigh‐qualityhabitatfrom90to1440musingMEAN,notamovingwindowaverage.

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Generatehabitatvariables BasedonpreviousworkwithCDOWlynxbiologiststhatidentifiedlikelyimportantexplanatoryvariablesforhabitatuse,Idevelopedasetoflandscape‐leveldatasetsbasedonregionally‐availabledatasets(Table2).ThesedataincludedcompositionalmeasuresoftheproportionofvariousvegetationtypescomputedfromLANDFIREexistingvegetationtypeclasses(30m),topographicvariablescalculatedfromtheUSGSNationalElevationDataset(30m),anddistancevariablescomputedfromColoradoDepartmentofTransportationhighwaysdata.Inaddition,Iexaminedtherelationshipofhabitatusetoindividualtreespeciestodiscernwhatspecificforestedvegetationstypeswereusedmore(orless)bylynx.Table2.Descriptionofthelandscape‐levelvariablesusedtoexaminehabitatuseoflynx.

Type Variable DescriptionBHD Censusblockhousingdensity(SERGoMv1.1,units*1000per

ha).DatasourcefromTheobald(2005),Bierwagenetal.(2010)Composition

RDENS Roaddensity(km/km2)Lf1 Water(Lakes,reservoirs,largerivers)LF2 Rock,snow,iceLF3 Urban/built‐upLF4 Agriculture(cropland,pasture)LF5 Forest(uppermontane)–Spruce‐fir,subalpine,lodgepole,

mixedaspen‐conifer,DouglasfirLF6 Forest(lowermontane)–ponderosapine,pinyon‐juniperLF7 ShrublandsLF8 Grasslands–includessub‐alpinemeadowsandalpinetundraLF9 Shrub(steppe)

Proportion

LF10 Riparian&wetlandsDEM Elevation(meters)SLOPE Slope–averageslopeindegrees(computedfrom30m)

Topographic

TWIP TopographicwetnessindexplussolarinsolationD4P5HA Forest(mesic)patchesatleast50haD4r2k HighwayswithAADT<2kD4R2_5K Highwayswith2k<=AADT<5kD4R5_10K Highwayswith5k<=AADT<10kDR410K HighwayswithAADT>10k

Distance

D4RDS Allnon‐highwayroads

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ResultsFollowingconvention,Idefinedlynxhabitatasareaswithinthe90%isopleth.Over

3.5millionacresinColoradoandNewMexicowerefoundtobecurrentlywithinlynxhabitat.Figure4showsthedistributionofthepopulation‐levelutilizationdistributionsurface,whileFigure5showsthenumberofindividualsthatwerefoundineachoftheUDpolygonsandFigure6depictsacumulativedistributionfunctionoftheUDvalues.Table3providesasummaryofthelandscapevariablesforlynxhabitat.

Theaverageelevationforlynxhabitatwas3,285m(10,780ft),withthemajority(68%or+and–1SD)ofhabitatlocatedbetween3,027and3,543m(9,900‐11,620ft).Theaverageslopeforlynxhabitatwas18.9(withthemajoritybetween12.8and25.1degrees).Theaveragetopographicwetnessindexvalue(TWI+)was3.38,rangingfrom2.64to4.12(lowvaluesindicatehighsoilmoisturenearthefootofslopesonnorthaspectswhilehighvaluesindicatelowsoilmoistureindicativeofridgetopsandsouth‐facingaspects).

Housingdensityinlynxhabitatwaslow,withameanvalueof0.011unitsperha(~1unitper80ha);themajorityofhabitatwasbelow0.102unitsperha(~1unitper10ha).Roaddensityinlynxhabitatwasalsolow,withameanvalueof0.51km/km2,andthemajorityofhabitatbelow1.22km/km2.

Theaverageproportionofforest(uppermontane)inlynxhabitatwas0.65,withthemajorityoccurringinareaswithatleast20%forested(uppermontane)cover.Habitatusewasalsoassociatedwithdistancefromlargepatches(>50ha)offorest(uppermontane)cover,withthemajorityofhabitatwithin3.35km,andtheaverageat0.36km.Theaverageproportionofgrasslandswas0.16.Therewaslittleassociationoflynxhabitatuseareaswithotherlandcovertypes. Lynxhabitatuseareasoccurredawayfromhighwayswithhightraffic(AADT>10k),averagingatleast43km,withmajorityatleast27kmaway.Thisdeclinedtobetween25.9and16.0kmaveragedistanceforotherhighwaytypes,withthemajorityofhabitatbeingatleast5.2kmfromthenearesthighway.Table4providesasummaryofthemostcommonlandcovertypes(fromLANDFIRE)foundtooccurinlynxhabitatuseareas.Appendix4providesscatterplotsforspeciesspecificforestedvegetationtypes.Subalpine/spruce‐firforestdominatestheUDpolygonsareawith43.3%.Otheruppermontaneandtundracovertypesareidentified,combiningtoover86%.Becauseofthegrainofthevegetationdata(aggregatedto2.25km2),covertypessuchasbarren/rockandtundracoverlikelyincludesmallstandsofforestandripariancover.

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Table3.Summaryoflandscapevariablesforthelynxhabitatuseareas.Unitsareinproportion(0.01.0)ifnototherwisedenoted.AlsoseeAppendix1forcumulativedistributionsofthesevariablesandAppendix2fordistributionmapsofeachvariable.

Type Variable Min -1 SD Mean +1 SD Max Housing density (units per ha) 0 N/A 0.011 0.102 10.531 Composition Road density (km/km2) 0 N/A 0.513 1.22 12.7Water (Lakes, reservoirs, large rivers) 0 N/A 0.005 0.03 0.9Rock, snow, ice 0 N/A 0.063 0.16 0.9Urban/built-up 0 N/A 0.002 0.01 0.7Agriculture (cropland, pasture) 0 N/A 0.003 0.04 0.95Forest (upper montane) 0 0.4201 0.653 0.89 0.99Forest (lower montane) 0 N/A 0.009 0.06 1Shrublands 0 N/A 0.008 0.06 0.95Grasslands 0 N/A 0.163 0.36 1Shrub (steppe) 0 N/A 0.061 0.14 0.94

Proportion (01)

Riparian & wetlands 0 N/A 0.031 0.06 0.56Elevation (meters) 1399 3027 3285 3543 4143 Slope (degrees) 0.1 12.8 18.9 25.1 37.6

Topographic

Topographic wetness index plus 1.40 2.64 3.38 4.12 15.20Highways with AADT ≥10k 0.20 27.86 43.88 59.91 77.00 Highways with 5k<=AADT<10k 0.20 14.59 25.96 37.32 51.80Highways with 2k<=AADT<5k 0.20 6.15 16.05 25.95 39.90Highways with AADT <2k 0.20 5.22 14.35 23.48 40.70All non-highway roads 0.03 N/A 1.88 4.26 35.00

Distance (km)

Forest (upper montane) patches ≥50 ha 0.00 N/A 0.36 3.35 27.10

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Figure4.Thepopulation‐levelutilizationdistributionfor118lynxintheanalysisdataset,shownwithmajorhighwaysandcountyboundariesforreference.Low‐intensityuseisshowninyellow,moderateinorange,highinblue.

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Figure5.Thenumberofindividuallynxthatwerefoundinpolygonsofthepopulation‐levelutilizationdistribution,shownwithmajorhighwaysforreference.

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Figure6.Thecumulativedistributionfunctionforthepopulation‐levelutilizationdistribution.Roughly50%oftheUDhasvalueslessthan12,about25%between12and30,andthetop25%between31and950.

Table4.Theproportionofdominantlandcovertypes(fromLANDFIRE)occurringinlynxhabitatuseareas.(Allremainingcovertypesarelessthan1%).

Existingvegetationtype PercentageSubalpine/Spruce‐firforest 43.3Barren/rock/tundra 13.3Alpinetundra(“turf”) 7.8Aspenforest 7.1Aspen‐mixedconiferforest 6.8Subalpine/uppermontaneriparian 6.3Snow‐ice 2.1Subalpine/spruce‐fir(mesic) 1.7Subalpinemontanemeadow 1.5

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Discussion/conclusionThisreportprovidesthefirstestimateoftheoverall,population‐levelhabitat

currentlyusedbylynxinColorado,withover3.5millionacres.ThemajorityofthecurrentlynxuseareasarelocatedonUSForestServicelands(Figure7).TwolargecontiguousareasofhabitatusearefoundintheSanJuanmountainrangeandtheCollegiatePeaksrangingnorthofMonarchPasstoVailPassandspanningI‐70nearLovelandPasstotheFrasierExperimentalForest.Threeothersmallerareaswereidentified,ontheGrandMesa,intheWestElksjustnorthofBlackCanyonoftheGunnison,andanareacenteredaroundRockyMountainNationalPark.Elevenof25downhillskiareasinColoradoarelocatedinlynxhabitat.

ThecentralfindingsofthisanalysisareconsistentwithpreviousreportsthattheCanadalynxreintroducedtoColoradohaveprimarilyusedhighelevationspruce‐firandaspenvegetationtypesashabitat.Thesereportsarebasedonvegetationdatacollectedduringaerialsurveysaswellas“ontheground”snow‐tracksurveys(CDOW2009;Shenk2009).

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Figure7.–TheutilizationdistributionforcurrentlynxhabitatinColorado,withforestserviceadministrativeboundaries.

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Highuseareas(thosewithlargerUDvalues)arecharacterizedbyahighpercentageofuppermontaneforest,highelevations,andhighmoisturepositions(i.e.lowTWI+values;Figure8andAppendix4).Withinforestvegetationtypes,thestrongestrelationshiptoUDweresub‐alpine/Spruce‐fir,andaspenandaspen/mixedconifervegetationtypes(Figure9).Figure8.ComparisonofUDforcurrentlynxhabitatversusuppermontaneforest(upperleft),Topographicwetnessindexplus(upperright),andelevation(lowerleft).

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Figure9.Forestvegetationtypeswithstrongpositiveassociationwithcurrentlynxhabitat:subalpine/spruce‐fir(left)andaspen/aspen‐mixedconifer(right).

LimitationsofanalysisAkeylimitationtothefindingshereisthatthedatarepresentonlyasampleoflynxin

thestate.Initially,100%oftheindividuallynxwerecollared,butthepercentoflynxinthestatethatweretrackeddiminishedovertime.Forexample,thenumberoflynxsampledin2010representsabout¼ofthenumbersampledduring2005(Table5).

Table5.Annualsummaryofnumberofindividualsandlocations.Year #individuals #locations

1999 9 782000 40 4432001 38 7982002 35 10992003 51 10112004 70 18112005 95 20822006 85 18912007 73 15462008 57 9362009 43 7862010 27 315

Wheninterpretingtheresults,itisimportanttorecallthattheanalysisisrestrictedto

areaswithlynxhabitatuse.Thatis,even“low”useareasprovideimportanthabitat,itisjustrelativelylowercomparedtohighuseareas.Also,rememberthatwhenthinkingabouttherelationshipbetweenuseandthevariouslandscapevariables,thevariouscovertypesarerestrictedtothehabitatuseareas,notthefullextentofcovertypeswithinabroader

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area(e.g.,corereleasesite,southernrockiesecoregion,etc.).AreasthatareoutsideoftheUDpolygonsidentifiedinthisanalysismaystillbeused,andtheUDpolygonsofhabitatusemightchangewithfuturedistributionsoflynx.

Becarefultointerpretthelandscapevariablesthatareestimatedoriginallyat30mresolution(fromLANDFIRE)becausemanyfine‐grainvariables,suchasnarrowriparianareasarenotrecordedinthesedata.Also,thesedatadonotcapturevariationinunder‐storyvegetation,ratherthesatelliteimagerypredominatelycapturesover‐storyconditions.

RecommendationsforfurtheranalysisTherearethreelogicalnextstepsfortheanalysisoflynxdistributionsinColorado:(a)comparisonoftheseresultstofield‐collectedvegetationdataonunderstoryandtopographiccharacteristics;(b)predictionofsuitablelynxhabitatbeyondthecorereintroductionarea;and(c)examinationofmovementincludinghighwaycrossinglocations.

a. Afirststepistocomparethefindingsofthisreportbasedonlynxlocationsandlandscape‐levelvariablesagainstthesite‐scalehabitatdatacollectedbyCDOWduringsnow‐trackingoflynx(forwinterseasonsforallyears).Ateachsite,datawererecordedonthelynxtracked,slope,aspect,foreststructureclass(grass/forb,shrub/seedling,sapling/pole,mature,andoldgrowth),location,andelevation(Shenk2006).Thesedatahavebeencompiledintoadatabaseandsummarizedinreports(e.g.,Shenk2009).Currently,CDOWareconductingaqualitycontrolprocesstoenablemoredetailed,spatially‐explicitcomparisonofthesite‐levelhabitatvariablesagainstlandscape‐levelvariables(JakeIvan,personalcommunication).

b. Asecondstepistodevelopaspatially‐explicitmodelthatpredictshabitatusewithinthestateofColorado,basedontherelationshipsbetweenlynxlocationsandlandscapevariablessuchasthosedescribedinthisreport.Generally,thetypeofmodelthatisappropriatedependsonthespecificmanagementquestionbeingasked,aswellasthenatureandqualityofthedatabeingused.Inparticular,understandingwhetherthelocationdataarebestconsideredpresence‐absencedataorpresence‐only.“…ifpresence‐absencesurveydataareavailable,webelieveitisgenerallyadvisabletouseapresence‐absencemodellingmethod,sinceinthatcasethemodelsarelesssusceptibletoproblemsofsampleselectionbias,thesurveymethodwilloftenbeknownandcanbeusedtoappropriatelydefinetheresponsevariableformodelling,andwetakeadvantageofallinformationinthedata(Elithetal.2011;pgs45‐46).Thelynxdatasetusedinthisreportandthatwouldbeavailableforaspatialpredictivemodelhavesomesamplingbiasissues,butshouldnotbeconsidered“presence‐only”data–becauseofthesystematiccollectionoflocationsviaVHF/aerialmethodsandthecomplementarydatafromARGOS.Certainlytherearesomeissueswiththelocationdata–suchasafocusondatacollectedsouthofI‐70andlikelymissingARGOSlocationsinhightopographicrelief/densevegetation–butcomparedwithmostotherwildlifestudiesofhabitatusethedatabaseisrobustgiventhelargenumberofindividualsanddurationofthestudy.TheCDOWhasheldpreliminarydiscussionsinDecember/January2011aboutpossiblemodelingapproachesandcandidatevariables.Aparticularchallengeistounderstandthe

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potentialhabitatuseoflodgepolepine–sinceitissoprevalentinforestsnorthofI‐70,yetmuchoftheexisting(1999‐2010)locationsaredominatedbylocationsneartheSanJuancoreareathathasverylittlelodgepolepine.Dataonforeststandage/structureareapotentialsurrogateforunderstoryvegetationtypesthatarethoughttobeimportantforhigh‐qualityhabitat(forsnowshoehares).

c. Athirdstepistoexaminelynxmovementinrelationtotransportationandotherpotentialconflictinglanduses.Giventhespatialandtemporalresolutionofthelynxlocations,itisreasonabletoexaminethedatasetforsomebroad,landscape‐levelquantificationofhighwaycrossings.But,thedataarenotsuitedtoconductanalysestoidentifyspecificlocations(<~10km)wherelynxmaybecrossinghighwaysandtoexaminehowotherlandusesmightbeinfluencinghabitatquality.

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Elith,J.,S.J.Phillips,T.Hastie,M.Dudik,Y.E.Chee,andC.J.Yates.2011.AstatisticalexplanationofMaxEntforecologists.DiversityandDistributions17:43‐57.Getz,W.M.andC.C.Wilmers.2004.Alocalnearest‐neighborconvex‐hullconstructionofhomerangesandutilizationdistributions.Ecography27:489‐505.

Getz,W.M.,S.Fortmann‐Roe,P.C.Cross,A.J.Lyons,S.J.Ryan,andC.C.Wilmers.2007.LoCoH:Nonparameterickernelmethodsforconstructinghomerangesandutilizationdistributions.PLoSONE2(2):e207.Millspaugh,J.J.,R.M.Nielson,L.McDonald,J.M.Marzluff,R.A.Gitzen,C.D.Rittenhouse,M.W.Hubbard,andS.L.Sheriff.2006.Analysisofresourceselectionusingutilizationdistributions.JournalofWildlifeManagement70(2):384‐395.Shenk,T.M.2006.WildlifeResearchReport2005­2006.ColoradoDivisionofWildlife,45pgs.

Shenk,T.M.2009.Lynxannualreport2008­2009.ColoradoDivisionofWildlife,55pgs.Theobald,D.M.2005.LandscapepatternsofexurbangrowthintheUSAfrom1980to2020.EcologyandSociety10(1):32.[online]URL:http://www.ecologyandsociety.org/vol10/iss1/art32/.