Journal of Biogeography. 2019;46:2735–2751. wileyonlinelibrary.com/journal/jbi  | 2735© 2019 John Wiley & Sons Ltd

Received:5July2016  |  Revised:22July2019  |  Accepted:16August2019DOI: 10.1111/jbi.13706

M E T H O D S A N D T O O L S

Novel summary metrics for insular biotic assemblages based on taxonomy and phylogeny: Biogeographical, palaeogeographical and possible conservational applications

Jason R. Ali1  | Miguel Vences2

Handlingeditor:RichardLadle

1DepartmentofEarthSciences,UniversityofHongKong,HongKong,China2ZoologicalInstitute,BraunschweigUniversityofTechnology,Braunschweig,Germany

CorrespondenceJasonR.Ali,DepartmentofEarthSciences,UniversityofHongKong,PokfulamRoad,HongKong,China.Email:jrali@hku.hk

Funding informationUniversityofHongKong,Grant/AwardNumber:2018HKUScienceFacultyEUtravelaward

AbstractUsing the land‐boundvertebrateson themarine islands asmodel organisms, twometricsarepresented thatpermitquantitativeandsuccinct synopsesof the ‘evo‐lutionarymaturity’ofthehostedfaunalassemblages.Inturn,thesereflectthegeo‐physical settings and geological developments of the substrates. The assemblage lineage‐taxonomy spectrum(ALTS)isbasedontheconstituentlineages’taxonomicdis‐tinctivenessanddiversity.Individuallineageswithinassemblagescaninmostcasesbeassignedtooneofsixcategories,LT1‒LT6: LT1isanon‐endemictaxon,whereasLT6 comprisesmultiple endemic genera froma family that arose elsewhere. If re‐quired,theschemecanbeexpanded:LT9isanendemicorder.Thedatacanthenbecombinedtoprovideanassemblagespectrum,forexample,00:08:38:30:08:15[13]. Here,thefirstsixvaluesdenotethenumberoflineagesassignedtoeachcategoryexpressedaspercentagesoftheoveralltotal,withthesumoftheprocessedlineageslistedastheseventh(inbracketsandbold).TheALTSmetrichighlightsefficientlythekeyfeaturesofamarineisland'sbiologicalassemblage.Notably,thecontrastbetweenspectraforsuitesongeologicallyandgeo‐physicallyvariedislandtypescanbestrik‐ing,forinstancethesquamatesuiteontheyoung,proximateorogenicmarginislandofTaiwaniscoded78:16:05:00:00:00[37]whereastheoneonthedistantlylocated,LateEocenecompositeterraneislandofNewCaledoniais00:11:00:11:33:44[9].Toovercome the subjectivity that is inherent in assigning supraspecific ranks, an al‐ternativeassemblage lineage‐age spectrum (ALAS)isalsointroducedthatmakesuseofthebinarylogarithmvaluesofthecolonizationtimesoftheislandlineages(0–2,2–4,…,32–64,>64Ma).Itisrepresentedusingaseven‐plus‐two‐numbercode,forinstanceMadagascar'ssquamatesare00:06:00:00:19:62:13[19(16)];mostcoloniza‐tionstookplaceinthePalaeogene(66–23Ma);thereare19lineages,butonly16arepresentlyage‐dated. Inadditiontomarine‐islandbiogeographystudies, theALTS–ALASspectrumapproachispotentiallyusefulforencapsulatingbiotasinothersortsof insularsetting(e.g. lakes,mountaintops),andforevaluatingpalaeogeographicalmodels.Furthermore, itmayhelpemphasize theconservationvalueof an island'sfaunalassemblage.

2736  |     ALI And VEnCES

1  | INTRODUC TION

Marine‐island faunas and floras attract much interest because oftheinsightstheyprovideintovariousimportantbiologicalphenom‐ena(e.g.Darwin,1859;Kueffer,Drake,&Fernández‐Palacios,2015;Losos&Ricklefs,2009;Wallace,1880).Eachsuiteresultsfrommul‐tipledispersaleventswithallofthesuccessfulcolonizationsleadingto one or more descendent species (Madagascar has >430 nativesquamatespeciesthataretheresultof19colonizations).Arguably,an island's biotic assemblage strongly mirrors the landmass’ geo‐physicalsettingandlong‐termevolution.Forinstanceyoungvolcanicoceanislandscanonlyhavebeenoccupiedrecentlyandmost,ifnotall,ofthelineageswilldifferonlyslightlyfromtheirclosestoff‐islandrelatives.Incontrast,oldlandmassesmayhostasizeablefractionofdistinctivecomponentsduetotheirancestorshavingarrivedappre‐ciably earlier, say in thePalaeogeneorCretaceous (66.0–33.9Ma;145.0–66.0Ma;Walker,Geissman,Bowring,&Babcock,2018).Here,deep‐time changes in a region's ocean‐current configuration mayalsohaveinfluencedstronglytheinfluxofcolonizerstoanisland.

Presently, a formal shorthand system does not exist to sum‐marize an assemblage. Associated statements are thus ostensiblydescriptive, for example, ‘the biota shares many similarities withthat of the nearbymainland’, ‘for several groups endemism levelsare>90%’or ‘the landmasshostsasmallnumberofrelictualtaxa’.Consequently,theyoftenfailconveytheintrinsiccomplexitiesofasuiteandthephysicalinfluencesthathaveshapedit.Toaddressthisissue,primarilytofacilitatediscussionsofthebioticassemblagesonandbetweenislands,wesoughttodevelopsimple,easy‐to‐applynu‐mericalspectrumschemesthatdistilthekeyelementsofeachbioticsystem.Ourmainaimisforthemtobeappliedbybiogeographersworkingonmarineislands,particularlythosewhoareinterestedinhowbiodiversityisshapedbyalandmass’ontogeny(e.g.Borregaard,Matthews,&Whittaker,2016;Whittaker,Triantis,&Ladle,2008),aswellasbytheoceanicandatmosphericsystemsthatwasharoundandover them (e.g.Ali&Huber, 2010).Additionally, theymaybeofvaluetobiologists investigatingother insularsystemtypes (e.g.lakes,mountains), researchersevaluatingpalaeogeographicalmod‐els,andpossiblyeventoconservationscientists.

2  | TERMINOLOGY, MODEL SYSTEM AND R ATIONALE

2.1 | Terminology and definitions

Tobeabletoconciselydiscussthemetricsproposedherein,wewilluseaseriesoftermsinspecificwaysthatrequirepriordefinition.Forclassificationsofisland types,seeAli(2017,2018).Indescribingthe

settingsof islandsandarchipelagos,weoftenuse thephrasegeo‐physical.Here,thefirstsyllablereferstotheEarth,whilethesecondpartconcernseitheraphysicalspaceoraphysicalprocess.Thetermis especially useful for biogeographical studies because it encom‐passes (palaeo)geographical, (palaeo)climatological, (palae)oceano‐graphical and geological (including geotectonic and geodynamic)processes.Allcanhavemouldedanisland'sbioticassemblage,andinmany cases two ormoremay have operated. It is emphasized,though,thatthistermasusedhereinisnotequivalenttogeophysical,whichreferstooneofEarth'sphysicsproperties,forexample,grav‐ity,electrical,magneticanddensity‐velocity.

Concerning the biological assemblages, lineage refers to a sin‐gle lineofdescentwithin the treeof life,heremostlyusedtode‐fine evolutionaryunits that represent a singleoriginon an island.This includes lineages composed of native non‐endemic speciesplusthosecomprisingendemicspecies.Concerningthelatter,somemaybelongtoendemicgeneraorendemicfamiliesanddiversifica‐tionmeansthattheycomprisemultiplesub‐components.Thekindofmetricintroducedhereiniscalledaspectrum,anditgroupsislandlineages using two independent criteria. One, the assemblage lin‐eage‐taxonomy spectrum(ALTS),makesuseofalineage'staxonomicrankand its levelofdiversification;variouscategoriescanthusbedefined(LTs).Theother,theassemblage lineage‐age spectrum(ALAS),isbasedonalineage'sageofcolonization,againwithseveraltypes(LAs).Thegoalof applying these spectra is to summarize theevo‐lutionary maturityofanassemblageof taxa.This termbuildsuponthe island maturityconceptasoftenusedinbiogeographical litera‐ture,butdoesnotrefertotheislanditself(Whittakeretal.,2008),nortothecompletenessofitsbiotacomparedtootherlandmasses(Trøjelsgaardetal.,2013).

2.2 | Utilizing land‐locked vertebrates on islands as a model

Although marine islands often contain numerous biological com‐ponents, the land‐locked vertebrates are arguably those that aremostcloselytiedtothesubstrates(plantsmaybephysicallybound,butformanytheirpropagulescanreadilybedispersed).Thustheyare optimally suited for a classification that aims to capture thegeo‐physical setting of an insular landmass and its geological de‐velopment.Vertebratesthatroutinelycrosssea‐waterbarriers(e.g.pinnipeds,turtles,manybatandbirdspecies,andsomefreshwaterfishes)arelessusefulbecausetheirtendencytomigratein/outofanislandwouldaddmuch‘noise’tothespectraweplantoevaluatetheislandsystemswith.

For the analysis we use: (a) the amphibians, which, althoughrare on the distant volcanic ocean islands due to their salt‐water

K E Y W O R D S

assemblageclassification,conservationtool,deep‐timevicariantlineages,endemicbiotas,insularbiotas,islandbiogeography,nativespecies,overwaterdispersedlineages,recentarrivées,relictlineages

     |  2737ALI And VEnCES

intolerance, are present onmanyof theother typesofmarine is‐lands; (b)a largesub‐setof thesquamatereptilesand (c) thenon‐flying,non‐aquaticmammals.Therewould,ofcourse,bescopeforincluding other sorts of land‐bound vertebrates, for instance theratite birds.However, focusing on large, easily defined groups fa‐cilitates the presentation of our basic idea. Furthermore, the tax‐onomies and phylogenies of the chosen faunas are generallywelldocumented.Incomparison,thesamelevelofinformationdoesnotexistformanyotherbioticcomponents,especiallytheinvertebrates.

Notably,theanimalgroupsselectedasexampleshereinseldommake overwater passages (e.g. Samonds et al., 2013), thereforethoselineagesthatarepresentonanislandwillresultfrom:(a)apro‐longedmassinvasionthatterminatedabruptlyfollowingtheflood‐ingofalandbridgeorthemeltingoficebridgeduringthetransitionfromaglacialmaximumtoaglacialminimum;(b)arare‘sweepstakes’colonizationevent (Simpson,1940) involvingagravid individualorsmallgroupor(c)arelong‐isolatedformsthatowetheirexistencetoadeep‐timevicarianceevent.

2.3 | Assemblages on shallow‐platform island clusters

Forthegoalofcomparingislandbiotas,thescaleandunitforanaly‐sismatters.Manymodern‐day islandshavebeen intermittently insubaerial contact in the recent past, and it thereforemakes littlesensetoanalysetheirbiotasseparately.Sinceabout3Ma(mid‐LatePleistocene:Walkeretal.,2018),numerousclimate‐changerelatedice‐sheet growth/retreat cycles (Lambeck, Esat, & Potter, 2002)haveeachresulted inasignificantverticaloscillationof theglobal

sea level. Through this interval the pattern has been somewhatcomplicated(Elderfieldetal.,2012),butsincec.700kathefluctua‐tionshaveacquiredaperiodicityofaround100kyr,withtheoceansurface ranging from its present height,which is the approximatepeakthewatersriseto,downtothelowestlowsof−90to−125m(Bintanja, vandeWal,&Oerlemans,2005); themost recentnadirdatesfromjustc.20ka.Asaconsequence,thoseislandgroupsthatareconnectedbyshallowseabed,forinstancethewesternandcen‐tralGalápagoschain,andthe ‘granitic’Seychelles (Figure1)wouldhave formed singlemassifs (verifiedusing theGeoMapApponlinesoftwareofRyanetal.,2009;thesystem'smenuallowstheprimarydepth‐sounding data sources to be identified). In such cases, it isproposedthattheassemblagesonsuchclustersbetreatedassingleentitiesratherthanmultipleones.Importantly,manyofthespecies’subpopulationson the individual islandswould likelyhavemergedduringthe lowsandthiswouldhaveresulted inwidespreadgene‐poolreconsolidation(Ali&Aitchison,2014,provide insightsbasedon an analysis of the geology, geography and reptile faunaof theGalápagosarchipelago).

2.4 | Rationale underpinning the proposal of ‘spectrum’ metrics

Fundamentalfeaturesofanyisland'sbiotaareitsdistinctiveness,itsdiversity andwhetherornot its constituent endemic species formmonophyletic groups (thus indicating in situ diversification). Theuniquenessofanislandlineageisdifficulttocapture,butthetaxo‐nomiclevelatwhichitisdifferentiatedfromitsclosestrelativesonthemainland/other islandprovidesaproxyfor this.For instance,a

F I G U R E 1  Locationofthevariousislandsandarchipelagosthatarementionedinthetext.ThelatitudeandlongitudemarkersonthisRobinsonprojectionmaphave45°spacings[Colourfigurecanbeviewedatwileyonlinelibrary.com]

Hawaii

South SandwichIslands

Gulf ofGuinea

Canaries

GalápagosCocos

HispaniolaLesser

An�lles

Svalbard

Mauri�us

Madagascar

Comoros

Socotra

Seychelles

Sri Lanka

Hainan

mainlandJapan

Jeju

Ryukyus

Taiwan

Timor

NewZealand

Grde Terre,New Cal.

Buru

Izu-BoninIslands

MarquesasSociety Islands

Juan FernandezIslands

2738  |     ALI And VEnCES

non‐endemic species that is present on an insular landmass is, bydefinition,effectivelyidenticaltoconspecificselsewhere.Incontrast,membersofanendemicfamilystandoutgeneticallyand/ormorpho‐logically,andmaywelloccupyunusualecologicalniches.Thediver‐sityofanislandlineagecanthusbecharacterizedbythenumberofspecies,generaandfamiliesitcontains.Determiningthestatusofamultispecieslineage,whetheritismonophyleticintheislandsystemunderconsiderationorparaphyleticwithrespecttotaxaoccupyingageographicalrangeoutsideofthatsystem,isfacilitatedbyphyloge‐neticframeworksthatexistformanygroups,particularlytheverte‐brates(e.g.Hamilton&Buell,2012;Hedges,Marion,Lipp,Marin,&Vidal,2014;Pyron,2015;Pyron,Burbrink,&Wiens,2013), includ‐ing extirpated species (e.g.Austin&Arnold, 2006).Notably, a sig‐nificantfractionofgenerarecognizedinpasttaxonomicframeworkshavebeenshowntobenon‐monophyletic (e.g.Pyron,Burbrink,etal.,2013).Aswillbeseenbelow,accommodatingsuchinformationiscriticalincalculatingtheproposedspectrummetrics.

3  | PROPOSAL FOR A TA XONOMY‐BA SED METRIC TO DESCRIBE BIOTIC A SSEMBL AGES

Thissectionexplainshowlineagesareassignedtolineage taxonomy categories (LTs)basedontheirdistinctivenessanddiversity,andhowthatinformationiscombinedtocharacterizeanislandassemblage.

3.1 | Proposed lineage taxonomy categories

• LT1–LT3:Thespeciesbelongtoanon‐endemicgenus.Thecate‐goriesLT2 and LT3 also includemembersof supposedendemicgeneraorfamilies(LT4andhigher,seebelow)thatareproventobenestedwithinagenusorfamilythatoccurselsewhere.Intheseinstancesphylogenyoverrulestaxonomy.

• LT1: Island lineagecomprisesanativenon‐endemicspeciesthatispresentalsoonthemainlandorother insular landmasses, for

example,theChinesecobra,Naja atra,onTaiwanandtheArcticfox,Vulpes lagopus,onSvalbard(Figure1).Almostinvariably,suchlineageswillhavearrivedgeologicallyrecently,withmostcoloni‐zationsresultingfromlandbridgeoricebridgeformationduringoneofthelateQuaternaryglacialepisodes.Consequently,toolit‐tletimewillhavepassedforappreciabledivergencetohavetakenplacerelativetoconspecificselsewhere.

• LT2:Islandlineagecomprisesasingleendemicspecies(Figure2).Differentiationlikelyresultsfromanagenesisoranacladogenesis(seeStuessy,Crawford,&Marticorena,1990),butnaturalextirpa‐tionofasisterspeciescouldalsobeacause.ExamplesincludethegeckoSphaerodactylus pacificusonCocosIsland,andthepitviperTrimeresurus trigonocephalusonSriLanka(Figure1).

• LT3: Island lineage comprisesmultiple endemic species and re‐sultsfrominsitucladogenesis (seeStuessyetal.,1990).Theis‐landlineageiscongenericwithtaxaonotherlandmasses(Figure2).Examples include thePhelsuma geckosonMauritiusand theMesalinawalllizardsonSocotra(Figure1).

• LT4–LT6:Thespeciesbelongtoagenusorgenerathataroseontheisland.Theirfamily,though,isnon‐endemic.

• LT4: Island lineage comprises an endemic genus that is repre‐sented by a single species (Figure 2). Inmost cases itwill be amonotype, but it is possible that descendent lineages occupyother landmasses.TwoexamplesarethechameleonArchaius ti‐grisontheSeychelles,andtheskinkHakaria simonyionSocotra(Figure1).

• LT5:Islandlineagecomprisesanendemicgenusthathasdiversi‐fiedintomultiplespecies(Figure2);forexample,theHaemodracon geckosonSocotra(Figure1).

• LT6: Island lineage comprisesmultiple genera that originated insitu (Figure 2). Exampleswould be the diplodactylid geckos onNewCaledonia(Bavayia,Correlophus,Dierogekko,Eurydactylodes,Paniegekko and Rhacodactylus)andthelandandmarineiguanasontheGalapagos(Conolophus and Amblyrhynchus)(Figure1).

If required, the scheme can be expanded to higher taxonomiclevels:

F I G U R E 2  Summaryoftheninedifferentlineagetaxonomycategories(LT1–LT9)thatareusedtoconstructanassemblagelineage‐taxonomyspectrum(ALTS)[Colourfigurecanbeviewedatwileyonlinelibrary.com]

LT2: a singleendemic species

Taxonomicrank

LT3endemic species

LT4: singlespecies from asingle endemic

genus

LT5from a single endemic genus

LT7: a singleendemic family

LT8endemic families

LT9: a singleendemic order

LT6endemic genera

family hasits originselsewhere

order hasits originselsewhere

genus hasits originselsewhere endemic

genus

Species

Genus

Family

Order

LT1: a non-endemic species

     |  2739ALI And VEnCES

• LT7:Asingleendemicfamily(Figure2;e.g.LeiopelmatidaefrogsonNewZealand;Figure1).

• LT8: An endemic lineage comprising multiple endemic families(Figure2;e.g.lemursonMadagascar;Figure1).

• LT9:This labelwouldapplytoasingleendemicorder(Figure2).However, of the animal groupsunder consideration, such a lin‐eageappearsnottoexistonamarineisland

AswithLT4,taxaassignedtoLT5–LT9allowforderivedlineagesthatarepresentelsewhere.

3.2 | Combining the data on lineage categories into an ALTS

As the lineage taxonomycategories are tobe combined toprovideameasureofanassemblage'sdistinctivenessanddiversity,whereagenusisrepresentedbytwoormoresubclades,thusrequiringsepa‐ratecolonizations,itisproposedthatthehighestrankingonebeusedasthe lineagecategory.For instance,onHispaniola (Figure1) thereare>40speciesofAnolis lizard (Hedges,2017); in thephylogenetictree of Pyron, Burbrink, et al. (2013) they are assigned to at leastseven lineages, themaximum levelbeingLT3.Whileacknowledgingtheargumentthatallsubcladestaxonomicallygroupedwithinagenusshouldbeincludedintheevaluation,thismayintroducedistortions,particularly for some of the land‐bound animals that appear suitedtomakingoverwaterjourneys(seeCensky,Hodge,&Dudley,1998).Furthermore,there isapractical issuerelatedtothefactthatmany

publishedtreesdonotincludeallspeciesrecordedonanisland.Forin‐stance,withtheSphaerodactylusgeckosonHispaniola(Hedges,2017)11speciesfeatureinPyron,Burbrink,etal.(2013),but24donot.Insuchcircumstancescarryingoutafullanalysiswouldbeimpossible.

Toenablecomparisonsofassemblagesonseparate islands,oramongelementsofabiotaonthesamelandmass,weproposeusingspectrumcodes(Table1).Inthesimpleversion,itwouldcompriseastringofsevenintegers,forexample,00:08:38:30:08:15[13].Thefirstsixvaluesrepresentthenumberof lineagesassignedtoeachofthesixcategoriesaboveexpressedaspercentagesoftheoverallnumberofthoseexamined(roundedtothenearest1%),withthelat‐terlistedastheseventhfigureusingboldfontinbrackets(Table1).Forexample,76:18:06:00:00:00[17] ismadeupprimarilyofnon‐endemictaxathatbelongto17lineages.Incontrast,thesequence00:07:21:36:21:14[14]indicatesa14‐componentsuitewithalargefractionofhighlydistinctivelineages.Intheextendedversion,thetotalnumberofnativespeciesisalsoincludedinthebrackets,butthat number is not bolded, for example, 00:07:21:36:21:14[14, 251].InthesmallnumberofinstanceswhenLT7orhigherlineagesareidentifiedanenlargedcodeshouldbeapplied,thatis,7+1/2,8+1/2or9+1/2(Table1).Furthermore,itispossibletoplotthecode sequence values, which in the examples presented below(Figures4and5)isdoneusingstacked,colouredbarcharts.

4  | PROPOSAL FOR AN AGE‐ OF‐COLONIZ ATION BA SED METRIC TO DESCRIBE BIOTIC A SSEMBL AGES

Thissectionexplainshowlineagesareallocatedto lineage age cat‐egories (LAs),andhowthatinformationisbroughttogethertosum‐marizeasuite.

4.1 | Proposed lineage age categories

Anumber of options are available for defining lineage age categories(LA1,LA2,…)priortotheircombinationintoanALAS(Figure3).Onein‐volveslinkingthemtothegeologicalperiods,forinstancePleistocene‐Holocene,Pliocene,LateMiocene,MiddleMiocene,EarlyMioceneetc.Anotherwouldadoptuniformtimewindows,say5or10Myr.Athirdusescategoriesbasedonthebinarylogarithmvalueofalineage'sage,thatis,0–2,2–4,4–8Ma,etc.Thefirstwasdiscardedbecausethestartandendofeachperiodwerespacederratically:0,2.6,5.3,11.6,16.0,23.0Ma,etc.(Figure3).Forpracticalreasonsfixedintervalswerealsodiscounted:5‐Myrperiodsrequiresanunwieldy14‐numbersequencetocovertheCenozoic(start66Ma);10‐Myrvaluesreducethistoseven,butthereisaconcomitantblurringof informationforthesuitesonislandsthatareMioceneoryounger(Figure3);thisaffectsmanyofthevolcanicones,whicharecommonly<10Ma,andthoseinthetectonicallyactiveregionswhereemergencemayhavebeengeologicallyrecent.Binarylog‐arithmsoftheinferredcolonizationagesappearbestsuited,andwede‐fineALAScategoriesspanning0–2Ma(LA1),2–4Ma(LA2),4–8Ma(LA3),8–16Ma(LA4),etc.(Figure3).Thereareanumberoflogicalandpractical

TA B L E 1   InformationcontentoftheALTSandALASmetrics

Included information

ALTS %LT1:%LT2:%LT3:%LT4:%LT5:%LT6[Nn lineages]

ALTS(extended) %LT1:%LT2:%LT3:%LT4:%LT5:%LT6:%LT7:….[Nn lineages,Nnativespecies]

ALAS %LA1:%LA2:%LA3:%LA4:%LA5:%LA6:%LA7[Ne lineages(Nd included lineages)]

ALAS(extended) %LA1:%LA2:%LA3:%LA4:%LA5:%LA6:%LA7[Ne lineages(Nd included lineages),Nnativespecies:Nendemicspecies]

NoteThetaxonomy‐basedALTSliststhepercentagesofeachofthelineagecategories(atleastLT1‐LT6),whichareseparatedbycolons;thetotalnumberofnativelineages(Nn)isthefigureinbrackets;eachofthenon‐endemicspecies(LT1)countsasasinglelineage.TheschemecanbeextendedbyincludingcategoriesLT7orhigher,andbyrecordingthenumberofnativespeciesintheassemblage(addedtothebrack‐etedpart).Theage‐basedALASliststhepercentagesoftheendemiclineagesthatoriginatedontheisland(viadispersalorvicariance)duringthetimeintervals0–2Ma(LA1),2–4Ma,(LA2),4–8Ma(LA3),8–16Ma(LA4),16–32Ma(LA5),33–64Ma(LA6),and>64Ma(LA7).Inbrackets,thefirstvalueisthenumberofendemiclineages(Ne;non‐endemicspeciesarenotincluded—seetext).Thesecondvalue(Nd; bolded and in parentheses),isthenumberoflineagesthathavedivergence‐dateesti‐mateswiththeirnearestoff‐islandrelatives;NdactsasthedenominatorinthecalculatingtheALAS‐categorypercentages.WiththeextendedversionofALAS,thenumberofnativespeciesandthenumberofen‐demicspeciesarealsopresented(intheright‐handsideofthebrackets).

2740  |     ALI And VEnCES

advantagestoemployingsuchascheme,butitisnotedthatmolecularclockagesmayhavelargeerrorvaluesduetotheassociateddataandmethodsthatwereavailableforcalibration;thiscanbeespeciallyprob‐lematicforthosegroupswhereonlyolderstudiesareavailable.However,theerrorsassociatedwithage‐calibratednodesinphylogenetictreesin‐creasewithage,thusthechosenintervalsgosomewaytoreflectingthis.

4.2 | Combining the data on lineage age categories into an ALAS

TheALASisgeneratedinasimilarwaytotheALTS.Havinganuppercategory of >64Ma (LA7), an assemblage can then be convertedintoaseven‐numberspectrumcode,whichiscloselycomparabletothetaxonomy‐basedscheme.Theonedifference,however, is thatnon‐endemic species, including endemic subspecies, are omittedfromthespectrumgeneration.AswiththeALTS,twovariantsareprovided.Thesimpleoneappearsas25:50:25:00:00:00:00[11(8)].Here,11indicatesthetotalnumberoflineagesthatarepresentonalandmass;eightisthenumberoflineagesforwhichcolonizationagesareavailable(presently,itisrareforsuchinformationtobeavailableforall lineages). Intheexpandedversion,more information ispro‐vided,forexample,25:50:25:00:00:00:00[11(8),31,28].Inthiscase,31denotesthetotalnumberofnativespeciesthatarepresent,while28indicatesthosethatareendemic.

5  | APPLYING ALTS TO VERTEBR ATE FAUNA S ON DIVERSE ISL AND T YPES

Data for squamates, and in somecases amphibians,were collatedforaseriesofdiversephysicalislandtypesbasedaroundtheland‐mass’sizeandage/emergence/stabilityovergeologicaltime‐scales.

The influence the substrate hason the evolutionarydevelopmentofaland‐lockedvertebrateassemblageshouldthusbecomeappar‐ent.Alsonotethatinallofthepresentedcasesonlytheshortenedspectrumcodesareused.

5.1 | Assemblages on three proximate continental islands

The first three examples are the suites on the islands adjacent toacontinentallandmass:Hainan,TaiwanandSriLanka(Figure1).Intermsofareatheyareofasimilarmagnitude (3.3–6.5×104km2).Importantly, all are separated them from their respective hinter‐landsbyshallowseasandduringperiodsofloweredglobalsealevelthereshouldthushavebeenhighmigrationfluxesbothinandout.However,althoughsuperficiallyalike,theassemblagesexhibitnota‐bledissimilarities.

Hainan (c.33,200km2)offsouthernChinaisatypicalshelfisland:geologicallycontiguouswith thenearbycontinentandgeodynam‐ically stable (Ali, 2018). Thewaters separatingHainan frommain‐landAsiaarelessthan40mdeep(verifiedusingRyanetal.,2009).Processingoftheisland'ssquamates(Lu,Wang,&Shi,2004)yieldsmainly LT1lineages(88:06:06:00:00:00[17];Figure4).Theonlyen‐demicsareOphisaurus hainanensis(aglasslizard),andGoniurosaurus hainanensis and Goniurosaurus bawanglingensis(sistercavegeckos).

TaiwanIsland(c.35,900km2)resultsfromthecollision‐inducedcrustalthickeningofthesouth‐eastChinapassivecontinentalmar‐ginthatislocallybeingover‐thrustbytheLuzonarconthewest‐ernedgeof thePhilippineSeaplate (e.g.Lallemand,2014;Teng,1990).Ali (2018) labels it orogenicmargin.Although the associ‐atedemergenceandupliftstartedjust5Ma,therearepresentlymorethantwodozenindividualpeaks>3,500m.TaiwanconnectstomainlandAsia via seabed≤70mdeep (verifiedusingRyanet

F I G U R E 3  Threeoptionsforcategorizingalineagebasedonitsage.Theschemeinthelower‘row’utilizesthefollowingintervalsofgeologicaltime:PleistocenethroughHolocene,GT‐1;Pliocene,GT‐2;Late,MiddleandEarlyMiocene,GT‐3,GT‐4 and GT‐5;Oligocene,GT‐6; Eocene,GT‐7;Palaeocene,GT‐8andCretaceous,GT‐9(thetime‐scaleisfromWalkeretal.,2018).Fixedperiodsof5and10Myrareshowninthetwomiddlerowsofthefigure.Theonethatisemployedforthecalculationoftheage‐basedspectra,ALAS,isshownintheupperrowandusesbinarylogarithmvaluesofthelineageages:0–2Ma=LA1;2–4Ma=LA2;4–8Ma=LA3;8–16Ma=LA4;16–32Ma=LA5; 32–64Ma=LA6;64–128Ma=LA7.Forinstance,onedatedas13.6MawouldbeassignedtoLA4 [Colourfigurecanbeviewedatwileyonlinelibrary.com]

Plei.&

Hol.

Plio. LateMiocene

MiddleMio.

EarlyMiocene

Oligocene Eocene Paleocene Cretaceous(starts at 145.0 Ma)

LA1

LA2

7AL6AL5AL4AL3AL(>64 Ma)

Geol.divs.

5 m.y.10 m.y.

Binarylog.

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80Age (Ma)

     |  2741ALI And VEnCES

al.,2009),thusitsland‐lockedfaunaisprimarilyduetocoloniza‐tionsviarecentlandbridges.Analysisoftheterrestrialsquamates(TaiwanBiodiversityNational InformationNetwork,2016;Xiang&Li,2000)identifiesmainlyLT1lineages(78:16:05:00:00:00[37]; Figure 4), but the presence of LT2 and LT3 lineages (Achalinus snakesandTakydromus lizards) indicates low levelsofendemismandsmallamountsofinsitucladogenesis.

SriLanka(c.65,600km2) isalsoashelf island(Ali,2018),buttheassemblagespectrumforitssquamatesisnotablydifferenttoHainanandTaiwanwitha sizeable fractionofmiddle‐andhigh‐endlineages(49:16:20:04:05:05[55];Figure4;basedonDas&DeSilva,2010;Pyron,Burbrink,etal.,2013).Notably,therearethreeLT6 lineages: agamid lizards (six genera), shieldtail lizards (threegenera)andskinks(twogenera).UnlikeTaiwan,SriLankaisanan‐cient landmass andhasbeen subaerial throughout theCenozoicand beyond (Colorado Plateau Geosystems Incorporated, 2016)hence some of its lineages have likely been present for consid‐erable periods. The c. 200‐kmwide neck of seabed connectingthe island to southern India is <20m deep (verified using Ryanetal.,2009), thus itshouldbeeasyfor terrestrialvertebratestocross from/to the subcontinent during eustatic lows.Why thenaresomeof itsbioticcomponentssodistinctive (e.g.Bossuytetal.,2004;Goweretal.,2002;Pyron,Kandambi,etal.,2013)?Ali(2018)presentsevidenceforastrongenvironmentalfilterimped‐ingtransfersbetweentheislandandthemainsubcontinentduringthelateCenozoic.

5.2 | Assemblages on three volcanic islands atop deep ocean floor

Animportantgroupofislandsarethevolcanoes(activeorextinct)thathavebuilt‐up from thedeepocean floor. These landmasses

commonlydevelop in supra‐subductionzonesettings, forexam‐ple,theSouthSandwichandIzu‐Boninchains(Figure1),orabovemantle‐plume hotspots, for example, Hawaii group (Figure 1).

F I G U R E 4  Examplesoftheassemblagelineage‐taxonomyspectra(ALTS)plots.Thoseontheleft‐handsideareforvariousislandtypes(seetext).Mostdrawuponnon‐aquaticsquamatedata,butforthe‘Granitic’Seychelles,JejuandPríncipetheamphibiansalsoincluded(seeTable2forthecodedversionoftheALTSwhichalsoincludesthenumberofprocessedlineages,thevaluesalsobeingpresentedontheplotinbrackets).Ontheright‐handsideofthefigure,thelowersixplotsareforthenon‐flying,non‐aquaticmammals,non‐aquaticsquamatesandamphibiansonTaiwanandMadagascar.ThetwoplotsabovethisareforBuru(non‐aquaticsquamatesandamphibians)andTimor‐East(non‐aquaticsquamatesonly).[Colourfigurecanbeviewedatwileyonlinelibrary.com]

0 20 40 60 80 100

HainanTaiwan

Sri Lanka

MontserratMauri�us

Galápagos "core"

SocotraGrande Terre, New Cal.

"Grani�c" Seychelles

JejuBarbados

Príncipe

Assemblage Lineage-Taxonomy CategoriesLT1

LT4

LT7

LT2

LT5

LT8

LT3 (Non-endemic genus)

LT6 (Endemic genus/genera)

LT9 (Endemic family/families/order)

0 20 40 60 80 100

Taiwan: mamTaiwan: squa

Taiwan: amph

Madag: mamMadag: squa

Madag: amph

Unusual sortsof island

Remote islands withcont. basements

Volcanic oceanislands/pla�orms

Large proximalislands

0 20 40 60 80 100

BuruTimor-East

The lineage categories making up the assemblages on the various islands/pla�orms.The totals should be 100, but due to "rounding" some are 99 and others 101.

Spectra for three land-boundvertebrate groups on two

very different sorts of island

Using the assemblage spectra inpalaeogeographical modelling

[11]

[6]

[15]

[10]

[9]

[12]

[4]

[7]

[7]

[55]

[37]

[17]

[5]

[19]

[4]

[19]

[37]

[34]

[27]

[13]

Spectra for varioussorts of island

F I G U R E 5  Comparisonofthetaxon‐basedspectra(ALTS)withtheage‐calibratedones(ALAS)(seetextandFigures3and4).PresentedaredataforthesquamatesonMauritiusandtheamphibiansandsquamatesonMadagascar.Thebracketednumbersdenotethenumberofprocessedlineagesthatwereusedtogenerateeachspectrum[Colourfigurecanbeviewedatwileyonlinelibrary.com]

Assemblage Lineage-Taxonomy CategoriesLT1

LT4

LT7

LT2

LT5

LT8

LT3 (Non-endemic genus)

LT6 (Endemic genus/genera)

LT9 (Endemic family/families/order)

0 20 40 60 80 100

Mauri�us: squa (ALAS)Mauri�us: squa (ALTS)

Madag: frogs (ALAS)Madag: frogs (ALTS)

Madag: squa (ALAS)Madag: squa (ALTS)

[16]

[5]

[5]

[7]

[3]

Assemblage Lineage-Age CategoriesLA1 (0-2 Ma)

LA5 (16-32 Ma)

LA2 (2-4 Ma)

LA6 (32-64 Ma)

LA3 (4-8 Ma)

LA7 (>64 Ma)

LA4 (8-16 Ma)

The lineage types making up the assemblages on the variousislands and pla�orms. The totals should be 100, but due to"rounding" some may be 99 or 101.

[19]

2742  |     ALI And VEnCES

Biogeographically, they are characterized by: (a) substrates thatemergefromthewatersasblankslates;(b)theyhaveneverbeenconnectedtoacontinent,hencethecolonizersmusthavearrivedduetooverwaterdispersalorpassagealonganicebridge;(c)thelandareasare typically100–1,500km2,which is relatively small(cf. the islands discussed in the preceding section) and (d) it israreforthemtobeolderthan10Ma,severalintheCanaries(vandenBogaard, 2013) plus Sal andMaio in theCapeVerde group(Ramalho,2011)beingobviousexceptions.

MontserratisanactiveislandarcvolcanointhenorthernLesserAntilles(Figure1).The102km2 landmassisyoungwiththeoldestrocksdatingfrom5Ma(Wadge,1986);emergencemayhavebeenc. 3Ma (Ali&Meiri, 2019). Theprocessed squamate lineages (Ali&Meiri,2019)areprimarilyLT2(Figure4;14:86:00:00:00:00[07]).

Mauritius (c. 2,040 km2; Figure 1) is a c. 8 Ma mantle‐plumehotspotisland(Duncan&Hargraves,1990)inthesouth‐westIndianOcean.Therearenonativeamphibiansornon‐flying,non‐aquaticmammals.Allbutoneofthesquamatespeciesareendemicandtheseven processed lineages exhibit moderate to high levels of dis‐tinctivenessanddiversification (14:43:14:14:00:00:14[7];Figure4;datafromthecompilationofAli&Meiri,2019).Notablythereisanendemic family of snakes (LT7), Bolyeriidae,which comprises twomonotypicgenera,Bolyeria multocarinata and Casarea dussumieri.

TheGalápagos’centralandwesternislandssitonashallowplat‐formintheeasternequatorialPacific(Figure1).Liketherestofthechain,theyresultfrommantle‐plumehotspotvolcanism.Duringpe‐riodsofloweredrelativesealevel,the‘core’cluster(Ali&Aitchison,2014)exposesa landmassc.13,500km2 (thearchipelagocontains

other sizeable islands, but they are isolated by deep water); thisgroupofislandshostfoursquamatelineages.Severalriceratspeciesalso occur, but they have suffered greatly following the arrival ofhumans,whohaveintroducedvariouspredatoryorenvironmentallydestructive mammals (Dowler, 2015; Dowler, Carroll, & Edwards,2000). There are no native amphibians. The islands are remote(930kmwestofSouthAmerica)andalsopresentrathersmalltargetsforadriftanimalstogroundupon.Moreover,at≤4Ma(Geist,Snell,Snell,Goddard,&Kurz,2014)theyareyoung,sothe‘sweepstakes’process(Simpson,1940)thatisafundamentalfeatureofoverwaterdispersalcolonizationhasbeen runningonly forashort time.Thebiotic assemblage (00:00:75:00:00:25[04]; Figure 4; based on thecompilationofAli&Meiri,2019),indicatesthatnosquamatespeciesaresharedwithacontinentandthatmoderatetohighdifferentia‐tionhastakenplace.OfparticularnoteisaLT6lineageintheformoftheAmblyrhynchusmarineiguanasandtheConolophuslandiguanasthatrespectivelycompriseoneandthreespecies.Recentestimatesindicate that their colonizer ancestor diverged from their CentralAmericansistergroupc.8.25Ma(MacLeodetal.,2015).Astheold‐estlandmassinthechain,SanCristobal,isnomorethan4Ma(Geistetal.,2014),thelandingmusthavebeenonanow‐submergedislandashortdistanceeastof theextantarchipelago (seeChristieetal.,1992),orextinctionofamuchyoungermainlandsisterlineagemustbeassumed.ThetwoGalápagosgenerasplitc.4.5Ma.

5.3 | Assemblages on three isolated continental‐basement islands

Thissub‐sectionconsidersassemblagesonthreeisolatedcontinen‐tal‐basement islands.However, due to their differinggeo‐physicalsettings(Ali,2017,2018),theiremergencehistoriesareuniqueandthishasstronglyaffectedthehostedfaunalsuites.

Socotra (c. 3,800 km2) lies 230 km east of theHorn ofAfrica(Figure1).Ali(2018)categorizestheblockasamicro‐continentalter‐ranebecauseofitscomplexvertical‐motionrecordduetoitbeinglo‐catedonthesouthernriftflankoftheGulfofAdenspreadingridge,andadjacenttoamajortransformfracture(Manighetti,Tapponnier,Courtillot,Gruszow,&Gillot,1997;Ryanetal.,2009).AlthoughtheAfrica‐Arabia breakup started at about the Eo‐Oligocene bound‐ary (33.9Ma;Walkeretal.,2018),Socotra'sgeological succession(Leroyetal.,2012) indicatesthatmarineconditionspersisteduntilthe EarlyMiocene (23.03–15.97Ma). This iswhen the protractedphaseofcontinentalstretchingswitchedtoocean‐floorspreading;theattendantinfluxofwarmasthenospherebeneaththelithospherewouldhavebuoyed‐uptheregion,includingthecrustthatSocotraisfoundedupon.Ina26March2018emailtoJRA,SylvieLeroysug‐gested that parts ofwestern Socotra became subaerial c. 20Ma;by18–17Mamuchoftherestoftheislandwasexposed.Therep‐tilelineagedata(Pyron,Burbrink,etal.,2013;Razzettietal.,2011;Vasconcelosetal.,2016)arebiasedtowardsthemiddleofthespec‐trum: 00:25:33:33:08:00[12] (Figure 4). The five endemic generaare theHakaria skinks,Pachycalamusworm lizards,Ditypophis and Hemerophiscolubridsnakes,andtheHaemodracongeckos.Notably,

TA B L E 2  Taxonomy‐basedspectra(ALTS)fortheassemblagesofsquamatesonvariousislandsystems(squamatesandamphibianson‘Granitic’Seychelles,JejuandPríncipe)

Island/Island type Spectrum (ALTS)

Unusualislandtypes

Príncipe(Enigmatic−1) 00:100:00:00:00:00[11]

Barbados(accretionaryprism) 17:83:00:00:00:00[06]

Jeju(shelfvolcano) 100:00:00:00:00:00[15]

Isolatedcontinental‐basementislands

GraniticSeychelles(isolatedblock) 00:10:20:30:00:40[10]

NewCaledonia(compositeterrane) 00:11:00:11:33:44[09]

Socotra(micro‐continentalblock) 00:25:33:33:08:00[12]

Volcanicoceanislands

Galápagos‘core’(centralandwest‐ernislands;mantle‐plumehotspot)

00:00:75:00:00:25[04]

Mauritius(mantle‐plumehotspot) 14:43:14:14:00:00:14[07]

Montserrat(islandarcisland) 14:86:00:00:00:00[07]

Proximatecontinentalislands

SriLanka(shelf) 49:16:20:04:05:05[55]

Taiwan(orogenicmargin) 78:16:05:00:00:00[37]

Hainan(shelf) 88:06:06:00:00:00[17]

Note: SpectraaretranslatedintobarplotsinFigure4.

     |  2743ALI And VEnCES

fourofthesearemonotypes:Hakaria simonyi,Pachycalamus brevis,Ditypophis vivax and Hemerophis socotrae.Arguably,Socotra's rela‐tivelysmallareahasimpededdiversificationwithintheselineages.

New Caledonia's Grande Terre is a composite terrane island(Ali,2017;Figure1;c.16,660km2)thatemergedintheLateEocene(38.0–33.9Ma:Walkeretal.,2018),due to thenorthernsegmentof the Norfolk Ridge, in its entirety a >2,000‐km‐long ribbon ofthinnedcontinentalcrust(typically12‐to15‐km‐thick;verifyusingRyanetal.,2009), locallycollidingwiththeLoyalty islandarc.TheLateEoceneevent ledtotheobductionofthe ‘UltramaficNappe’,which comprises numerous fragments of a dismembered fore‐arc(e.g.Cluzel,Maurizot,Collot,&Sevin,2012;Whattam,Malpas,Ali,&Smith,2008),andtheformationofanarrowzonewherethecrustwas thickenedbyaboutanother10km (verifiedusingRyanetal.,2009).GrandeTerre'sisolationaccountsforthelackofamphibiansandland‐lockedmammals(Australia,thenearestlargelandmass,isc.1,200kmaway).Thereareninereptilelineages(Bauer,Jackman,Sadlier, & Whitaker, 2009, 2012; Bauer & Sadlier, 2000; Bauer,Sadlier, Jackman, & Shea, 2012; Sadlier & Bauer, 2002; Sadlier,Bauer,&Smith,2006),withmost categorizedaseitherLT5 or LT6 (00:11:00:11:33:44[09];Figure4).

The ‘granitic’Seychelles (Figure1) comprises fourmain islandsranging from10 to157km2, plus several smallerones.Thearchi‐pelagositsonasizableplatform(c.44,000km2) thatbecomesex‐posedwhensealevelfallstoaround−60m(verifiedusingRyanetal.,2009).ThecrustalblockwasisolatedfollowingitsbreakupwiththeIndiansubcontinentatabouttheCretaceous–Palaeogeneboundary,66Ma(Ali&Aitchison,2008).Biologicallyspeaking,theSeychellesarefamousfortheirdeep‐timevicariantsooglossidfrogs(twogen‐era,fourspecieseach;LT6)andindotyphlidcaecilians(threegenera,six species total; LT6; based on San Mauro, Vences, Alcobendas,Zardoya,&Meyer,2005;SanMauroetal.,2014)whoseprogenitorswerepresentprior to India's separation.Theoneotheramphibianspecies,thehyperoliidtree‐frogTachycnemis seychellensis,andallofthesquamates(Gardner,1986;Gerlach,2005,2007a,2007b,2008;Maddock,Day,Nussbaum,Wilkinson,&Gower,2014;Rochaetal.,2009;Rocha,Harris,&Posada,2011;Rocha,Posada,&Harris,2013;Townsend, Tolley, Glaw, Böhme, & Vences, 2011; Valente, Rocha,&Harris,2014)aredescendedfromoverwaterdispersedcoloniststhatarrivedatdifferenttimesintheCenozoic.TherearetwootherLT6 lineages, the first comprising the skink generaPamelaescincus and Janetaescincus, the second the gecko genera Ailuronyx and Urocotyledon.Thespectrum,00:10:20:30:00:40[10](Figure4),mir‐rorsthechain'sageandrelativeisolation.

5.4 | Assemblages on three unusual island types

The sectionpresents assemblagedata for three rare island types,tworesultingfromvolcanisminatypicalsettings,JejuandPríncipe,thethirdbecauseof itsuniqueplatetectonic locationonan intra‐oceanicfore‐arc(Barbados).

The volcanic island of Jeju has grown atop what is presentlythe submerged continental crust that floors the East China Sea

(Figure 1). The terrain, c. 1,850 km2 in area, is not related to ahotspotnora subduction system;Ali (2018) classifies it asa shelfvolcano island. Subaerial eruptions commenced c. 1Ma,with thelatestactivitydatingfromjustafewthousandyearsago(Koh,Park,Kang,Kim,&Moon, 2013; Sohn&Park, 2004). Bathymetric data(verifiedusingRyanetal.,2009)revealthattheseabedconnectingJejutothenearby landmasses is≤100mdeep.Thesquamateandamphibianoccurrencedata(JejuIslandNatureEnvironmentEcologyInformationSystem,2019;MinistryofEnvironmentoftheRepublicofKorea,2005)indicatethatthenativelineagesareexclusivelyLT1 (100:00:00:00:00:00[15];Figure4).Inlightoftheisland'sage,thisisnotunexpected.Mostofthespeciesarederivedfromcontinen‐talAsia,butsomemaybefromthemainarchipelagoofJapan.Thecolonizationslikelyoccurredwhenland‐connectionsformedduringrecentglacialperiods.

Barbados (432 km2) is another geo‐physical oddity and rep‐resents the Lesser Antilles arc's exposed accretionary prism (Ali,2017)(Figure1).Theisland'sbasementcomprisesmainlysedimen‐tarypackagesthatarepreservedinaseriesoffault‐boundwedgesthatwereoff‐scrapedas theoceaniccrustof theSouthAmericanplatewassubductedwestwardsbeneath theCaribbeanPlate (e.g.Kearey, Klepeis, &Vine, 2009; Speed& Larue, 1982). Later, afterthe trench had migrated a short distance eastwards due to thebuildof the thrust stack, the rockswereblanketedbymarine for‐mations(Donovan,2005;Speed,2013;Speed&Larue,1982).Theverticalmotionhistoryof thesub‐regionmayhavebeencomplex,aswouldbeexpected inafore‐arcsetting;Speed (2013)suggeststhatthemodern‐dayislandemerged700–350ka.Processingofthesquamatedata(Hedges,2017)yieldsalow‐endweightedspectrum:17:83:00:00:00:00[06](Figure4),whichisconsistentwithBarbados’youthfulness.

Príncipeisasmallisland(136km2)intheGulfofGuinea(Figure1)andformspartoftheCameroonLinevolcanicchain(Fitton,1987).Intra‐plateeruptionshavebuilt‐uptheedificefromtheflooroftheeasternequatorialAtlantic, although themechanismbywhich themagmatism was/is being generated is contended (Fitton, 1987;Njome& deWit, 2014). As a consequence, Ali (2017) labelled theislandEnigmatic‐1asassigningittooneofthemoreobviousgeotec‐toniccategorieswasnotpossible.ThesynthesisofFitton(1987)in‐dicatesthatsubaeriallyeruptedlava‐flowpackagesdatefromc.24,c.19and6–3Ma(Fitton,1987),hencethelandmasshaspotentiallybeenemergentthroughouttheNeogene.Theherpetofaunalassem‐blage, comprising five lizard, three snake and three frog lineages(Ali&Meiri,2019;Bell,Drewes,&Zamudio,2015;Gilbert&Bell,2018;IUCNRedList,2016)isentirelyLT2(00:100:00:00:00:0[11]; Figure4).Theprobable reason for therebeingnoLT3s is that theislandistoosmallforinsitucladogenesistohavetakenplace(Ali&Meiri,2019);lackoftimecanreasonablybeexcluded.

5.5 | Null spectrum islands

A minority of marine islands do not host native land‐locked ver‐tebrates, for instance those in the Hawaii, Society, Marquesa

2744  |     ALI And VEnCES

and Juan Fernandez groups. As such they are categorized as00:00:00:00:00:00[00]. This reflects the archipelagos’ isolationand/or youth. The first three are 3,700–5,800 km from the near‐estcontinent;thelastisonly600–700kmwestofSouthAmerica,butitslocationrelativetotheflowsoftheSouthPacificgyremeansthat it is effectively impossible for land animals to raft over to it;theoldestlandmassesinthefourclustersarec.6Ma.Notably,theyrepresentthefarendofarangethatstartswiththeeasilycoloniz‐able islands that are characterizedbynumerous low‐end lineages,forexample,Hainan,JejuandTaiwan.

6  | USING ALTS TO COMPARE A SSEMBL AGES

6.1 | Comparisons among various sorts of marine islands

ThenumericalcodingsandderivedplotsshowninTable2andFigure4emphasizethemajordifferencesbetweentheassemblagesonthevar‐ioussortsofmarineislands,implyingthattheschemehassomeworth.Importantly, it permits exact, succinct statements to be made, forexample: ‘ThesuiteonTaiwancomprisesprimarilyLT1 lineages,butlow‐leveldifferentiationhastakenplacewithinthreelineages’,or‘TheisolatedlandmassofNewCaledonia'sGrandeTerre,whichemergedinthemid‐Cenozoic,isdominatedbyLT5 and LT6lineages’.

6.2 | Comparisons among different faunal groups occupying the same island

Wheredifferentland‐lockedfaunalgroupsarepresentonanisland,insightsmightbegleanedthroughcomparingtheirassemblagespec‐tra.Forexample,dataforTaiwan'smammals(85:12:03:00:00:00[34]; Wilson&Reeder,2005;IUCNRedList,2016),non‐aquaticsquamates(78:16:05:00:00:00[37]) and amphibians (52:32:16:00:00:00[19]; Lue, 2016) are plotted in Figure 4. Although the three bar chartsindicatethatthesuitesaredominatedbyspeciesthatarealsopre‐sentonmainlandAsia,therearesomedifferences,withtheamphib‐ians inparticularhavingahigherproportionofendemics includingthree LT3 lineages: Hynobius salamanders, Rana pond‐frogs andRhacophorustree‐frogs.

OnMadagascar (587,000km2), thespectra for thesamethreegroups(Figure4;Crottinietal.,2012;Samondsetal.,2013)arelessalike,andcontrastdramaticallywiththoseonTaiwan.Asaconse‐quenceoftheislandbeingolderandmoredistantlypositioned,someofitslineagesarehighlydistinctiveandthespectrahavehadtobeextendedtoincorporatetheLT7 and LT8categories.Themammals(excluding the extirpated hippos due to their taxonomic ambigu‐ities)areallLT6orhigher (00:00:00:00:00:50:25:25[04];Figure4),and include the lemurs (LT8) that comprise five families, and theEupleridae carnivorans, which are LT7. The four mammal‐lineagecolonizations date from the EarlyMiocene or prior (Ali & Huber,2010;Pouxetal.,2005).Thesquamateshaveabroaderspectrum(11:05:11:05:16:16:26:11[19]; Figure 4) with some of the earlier

arrivéeshavingevolvedtoLT5‒LT8,inadditiontosomenewcomers(e.g.afewhousegeckosandanagamidlizard).Relativetothemam‐malsandthefrogs(00:20:00:00:40:20:20[05];Figure4),reptilesarefarbetterat colonizing remote islandsas is alsoevidencedby thesuitesontheGalápagos,Mauritiusandthe‘granitic’Seychelles.

6.3 | Emergence of notable/consistent patterns?

Althoughdataforonly13islandshavebeenpresented(Figure4),itisworthconsideringiffundamentalpatternscanbeextractedfromtheassociatedassemblagespectra.

1. If the landmass is separated from a continent by a shallowsea floor, during the recent glacial periods they would havebeen connected. Hence, many lineages will be present withmost being LT1s.However, as the suite on Sri Lanka indicates,additionalfiltersmayhaveexisted,thusoccasionallysomemiddleand high‐end lineages may also be present.

2. Islandswithdeep‐waterbarriersaredominatedbyendemics.Onislands<5Ma,theseareprimarilyLT2.Onsubstrates8–15Ma,in‐cludingsomenotespeciallylargeones(e.g.Mauritius,Galápagos‘core’,Socotra),endemicgeneraemerge.Theassemblagesontheevenolderislands/platformsoftencontainmultipleendemicgen‐era(e.g.NewCaledonia,Seychelles).

3. Large,oldislandslikeMadagascarhostendemicfamilies(thean‐cestorsofitsterrestrialvertebratesbegancolonizingintheearlyandmiddleCenozoic).Additionally,lateCenozoicoverwaterdis‐persershavearrivedandestablishedthemselves.

7  | AL A S: AN ALTERNATIVE TO ALTS

AnobviouslimitationtoALTSisthefactthatitisbasedontaxonomicinformation,which is an imperfect representation of evolutionaryhistory and age. Consequently, the application of non‐equivalentconceptsanddissimilarsourcesofdatamay leadtodifferences intheway that taxa are delimited (e.g.Humphreys& Linder, 2009),thus potentially impacting the accuracy and comparability of thespectrumcodings.Moreover,thestateoftaxonomicknowledgeofagrouporgroupsmayhaveaninfluence.Anexampleofthisispro‐videdbytheSooglossidaefrogsontheSeychelles.Currentlytheyareassignedtotwogenera,Sechellophryne and Sooglossus,andwithtwospeciesapiecethelineageisthusclassifiedasLT6. Inrecentyears,though, some authors have recognized a single genus, Sooglossus,inwhichcasetheywouldbecategorizedasLT5,orhaveseparatedthemintotwogenera,Sooglossus and Nesomantis,withrespectivelythree and one species each (Frost, 2016, and references therein),againLT6. A broadly similar scenario is associatedwith the skinks(c.1,600speciesworldwide).InHedgesandConn(2012)proposedthatthetraditionalsinglefamilybedividedintosevenfamiliesandthissparkedalivelydiscussion(e.g.Hedges,2014;Pyron,Burbrink,etal.,2013).TheSooglossidaeexampleillustrateshowaspectrumbased on taxonomic rank can introduce considerable partiality. In

     |  2745ALI And VEnCES

fact, assigning taxa to supraspecific rank is highly subjective (e.g.Vences,Guayasamin,Miralles,&delaRiva,2013);howagenus,fam‐ilyororderisdefinedwilldifferamongorganismgroups,historyandindividualtaxonomists.

Asolutiontothissubjectivityisaspectrumthatisbasedontheinstantsintimewheneachoftheislandlineagessplitfromtheiroff‐islandsistergroups:ALAS.AnadvantagesharedwiththeALTSap‐proachissimplicity,giventhatthedataneededforanALASspectrumcanbeinferredfromtime‐treesaswellasfromthefossilrecord.Theapproachworkswellforthesquamates00:06:00:00:19:62:13[19(16)]and frogs00:00:00:20:40:40:00[5(5)] onMadagascar (Figure5) asmostofthelineageshavebeenage‐dated(Crottinietal.,2012).OnMauritius (00:00:00:00:33:66:00[7(3)]; Figure 5), though, the situ‐ationisratherdifferent.Firstly,colonization‐agedataonlyexistforthreeofthesevenhostedclades.Secondly,allconflictwiththeisland'sageofc.8Ma(Duncan&Hargraves,1990).TheGongylomorphus and Leiolopismaskinkssplitrespectivelyfromthenearestrelatives47.3and38.9Ma,(Zheng&Wiens,2016),buttheseareprobablyover‐estimatesastheyarebasedpredominantlyonmitochondrialDNA.ForthePhelsumageckos(originoftheentireMascareneradiation),theiragesspan35‒21Ma(Zheng&Wiens,2016).Insummary,theMauritius squamate ALAS is largely incomplete and plagued withconsiderable uncertainty, and it is probable that assemblages onmanyotherislandsaresimilarlyaffected.

8  | OTHER APPLIC ATIONS FOR ALTS AND AL A S

8.1 | Applying ALTS and ALAS to other isolated biogeographical systems

ItisalsoenvisagedthatALTSandALAScouldsummarizebiologicalsystems in other geo‐physical settings. Perhaps themost obviouscaseswouldbethoseinlong‐livedlakes(e.g.Baikal,Tanganyika),onthemiddleandupperreachesofstand‐alonemountains(e.g.Kenya,Kilimanjaro,Kinabalu),orinlargeprotectedareas.

8.2 | Evaluating palaeogeographical models

The outlined schemes can also be used to test palaeogeographi‐cal models, especially for those tectonically active regions whereverticalmovementsaresometimesconsiderable.Youngislandsarelikely tohaveALTSdominatedbyLT1‐LT3 species.Older landsur‐faceswill typically host LT4 and higher lineages, given the longertimeavailablefordifferentiation.Forexample,Timor(30,800km2)andBuru (9,500km2) are twomicro‐continental terrane islands ineasternIndonesia(Figure1;Ali,2017).Theysit inoneofthemostgeotectonicallycomplexregionsonEarthwheretheEurasian,Indo‐Australian and Philippine‐Pacific plates are converging (e.g. Hall,2012).Inanearlierwork,Hall(1998)producedaseriesofland‐seamapsfortheregionandshowedmostofitsubmergedat15,10and5Ma, butwith Buru notably exposed in all three.More recently,however,Hall(2013)hasdepictedforthesamesnapshotsBuru(and

Timor)asbeingsubmarine.Interestingly,theassemblagespectraforthe two landmasses (Figure4), based respectivelyon thepublica‐tionsofKreyetal.(2012),andO'Sheaetal.(2015)andKaiser,Tighe,and O'Shea (2015), support the newer reconstructions. The line‐agesonbothislandsaredominatedbyLT1s,particularlythatofBuru(92:08:00:00:00:00[13];Figure4).OnTimor,however, thesuite isslightlymorematureandincludesfiveLT3s(70:09:22:00:00:00[27]; Figure4):thegeckogenusCyrtodactylus;andtheskinkgeneraCarlia,Cryptoblepharus,Eremiascincus and Sphenomorphus.

8.3 | ALTS and ALAS as tools for revealing the conservation value of island systems

Theterms‘endemism’and‘endemic’oftenplayacentralroleincon‐servation‐focused programmes and publications, especially thosedealingwiththebiologicallyrichregionsthatarethreatenedbyhu‐mankind (e.g.Myers,Mittermeier,Mittermeier,daFonseca,&Kent,2000).Manyhave argued that phylogenetic information should in‐forminitiativesanddiscussions(e.g.Faith,1992;Forestetal.,2007;Isaac,Turvey,Collen,Waterman,&Baillie,2007;Rollandetal.,2012;Vane‐Wright,Humphries,&Williams,1991).AstheALTSandALASsystems highlight key features of island's biology, theymight com‐plementexistingphylogeny‐basedmetricssuchas theEvolutionaryDistinctiveness and Global Endangerment (EDGE) classification ofspecies (Isaac et al., 2007).Once the various categories havebeenexplained, the exclusivity of some of the faunal suites, for exam‐ple, those on Socotra, Seychelles, NewCaledonia andMadagascar(Figures 4 and 5), is readily apparent. A spectrum‐based approachcouldbeusedtoextendtheEDGEclassificationfromsinglespeciestoentirespecies’assemblages,andanALASvariationbasedonanEDGEmetric(Gumbs,Gray,Wearn,&Owen,2018)wouldemphasizeanas‐semblage'sconservationrelevanceratherthanageofcolonization.

9  | FURTHER CONSIDER ATIONS

9.1 | Transparency and repeatability

Wheneveraspectrumispresenteditwouldusefulifeachofthelin‐eagecategorizationsthatareusedtocalculatetheALTSandALASbe appropriately documented, possibly in appendices, with thesupporting publications/authorities also being stated. ConcerningALAS,therewouldbemuchmeritiftheprincipalinformationsourceforthecladeageswasretrievedfromtheTimetreeofLifedatabase(TToL;Kumar,Stecher,Suleski,&Hedges,2017)asthiswouldfacili‐tatethecomparisonofresultsfromdifferentstudies.Iftherelevantinformationwereunavailable,thenothersourceswouldbecited.

9.2 | Extension towards age‐based spectra and phylogenetic diversity metrics

In the taxonomy‐based ALTS approach, taxonomic rank (endemicgenus,family,order)isusedasaproxyforevolutionarydistinctive‐nessofa lineage, influencedbothbycladeage,diversificationand

2746  |     ALI And VEnCES

ecomorphology.IncomparisonwiththeALTS,theage‐basedALASmissestwokeyelementsofanassemblage'sevolutionarymaturity.Thefirstistheamountofintra‐islanddifferentiationthatintheALTSiscapturedbydefiningthelineagecategoriesLT3,LT5,LT6 and LT8 inwhichmultiple species/genera/families have originatedwithin asystem. Adding this information for each geological period to theALASwouldmakethisapproachoverlycomplex,thusemphasizingthemeritsofthesimplifiedtaxonomy‐basedALTS.AlsoALASstrug‐glestoaccommodatethenon‐endemicspeciesastheirearliestoriginonanislandistypicallyunknown.Toacknowledgethisissue,wesug‐gestthatthebracketedpartofthespectrumalsoincludesthetotalnumberofnativespeciesplusthenumberthatareendemic.

Anotherdimensionmissedbythepure‘timebanding’categoriza‐tionoflineages(Avise&Johns,1999)asintheALASistheevolution‐arydistinctivenessof lineages.Lineagesmightbeveryoldbutstillphenotypicallyindistinguishablefrom,andoccupyingsimilarecolog‐icalnichesas theirancestorsandsistergroups.Alternatively, theymayhavedivergedintomanynoveladaptivezones,asisoftenob‐servedinislandradiations,andinsuchcasestheyaremorelikelytobeplacedinahighertaxonomicrank.Hence,despiteallshortcom‐ingsandsubjectivityofsupraspecificLinneanclassification,weareconvincedthattheevolutionarydistinctivenessofalineagecouldatleastinsomecasesbemoreeffectivelysummarizedinataxonomy‐basedspectrumthaninapurelyage‐basedone.

As amain advantage, the spectrum representationof both theALTSandALASmetricsisanintuitivewaytosummarizeandvisual‐izetheevolutionarymaturityofabiota.Amajordisadvantageisthatspectracannotreadilybeharvestedforcomputational,quantitativecomparisons.Nosinglevaluecanrepresentthemultidimensionalin‐formationcontainedinthespectra(taxonomicoragedistributionoflineages,totalnumberoflineages,totalnumberofspecies,numberofendemicspecies;andecomorphologicaldistinctivenessasitisoften,thoughinconsistently,containedintaxonomicranks).However,de‐pendingonthespecificevolutionaryquestion,usageofameasureofphylogeneticdiversitycancapturearelevantportionofthisinforma‐tionfromaphylogenetictree.AssummarizedbyKellar,Ahrendsen,Aust,Jones,andPires(2015)andTuckeretal.(2017),variousphylo‐diversitymetrics exist that quantify, in termsof branch lengths ordistances the richness, divergence and regularity of a community(Tuckeretal.,2017).Forthepurposeofunderstandingtheevolution‐arymaturityofislandassemblages,thesecouldbemodifiedtofocuson (a) those branches of a phylogenetic tree separating the islandlineages from their non‐island sister groups, for example, average,varianceor evennessofbranch lengthsof endemic lineages,or (b)onthewithin‐islandsplitstocharacterizethepatternsofintra‐islandradiations.Itis,however,beyondthescopeofthispapertoevaluatethepromiseofothersingle‐valuemetricsforthispurpose.

9.3 | Limitations with the lineage‐based assemblage metrics

Amajordrawbackwiththetwo lineage‐basedassemblagemetricsproposedhereinarethoseinstanceswheresevereextirpationshave

resultedfromtheactivitiesofhumankind,directlyand/orindirectly,for example the decimated rice‐rat populations on theGalápagos(Dowler, 2015; Dowler et al., 2000) and numerous land mammalgroupsintheWestIndies(Woods,2001).Asmanyareknownonlyfrom sub‐fossils, assigning them to anALTS or anALAS categorywouldbedifficult.Afurtherproblemrelatestointroducedspecies.Ifunderappreciated,thesewouldcreatea low‐endbiastoanyde‐rivedspectrum.ThisissueisparticularlyacuteintheMediterraneanbasinwhereoverthepastfewthousandyearsnumerousmainlandforms have colonizedmany of the islands due to the activities ofhumans(e.g.Corti,Masseti,Delfino,&Pérez‐Mellado,1999;Pinya&Carretero,2011).

Identificationofanotherissue,whichwelabelthesource‐uncer‐taintyphenomenon,arosefromtheanalysisofdatafortheRyukyuarchipelago.RunningbetweenTaiwanandthemainislandsofJapan(Figure1),thechainincludesseveralshallow‐platformgroupsthatareseparatedbydeepwater (verifiedusingRyanetal.,2009). Insuchcircumstances,itmightbeanticipatedthatasizeablenumberof endemicswould exist on each.However, a sizable number ofspeciesthatareexclusivetothechainarepresentontwoormoreislandgroups,forinstancetheskink,Plestiodon marginatus,andthetree‐frog,Hyla hallowellii (Goris&Maeda,2004). It thussuggeststhat overwater dispersal is taking place regularly between theclusters,but this isnotunexpectedas theKuroshioCurrent runsthrough the archipelago (Cook, 2015;Qui, 2001) and the regioneach year experiences several typhoons (Kim & Seo, 2016). Theproblem,though,withapplyingtheproposedclassificationschemeisdecidingwhereindividualspeciesaroseasinmanycasesthedataareambiguous.It ispossible,however,tocarryoutananalysisofsome island groups using assemblage sub‐sets. For instance, theYaeyama platform islands towards the south‐west of the chainyieldanALTSof50:30:20:00:00:00[10].Interestingly,theadjacentMiyakocluster isbroadlysimilar,40:60:00:00:00:00[05],but it isbasedon fewerusable lineages.Unfortunately, the suiteson theplatforms to thenorth‐east (Okinawa,Akajima,TokashikjimaandAmami,whicharealldownstreamoftheKuroshioCurrent),cannotbeprocessedduetotheuncertaintiesregardingtheoriginsoftheirlineages.

9.4 | Assemblage metrics and possibilities for their automated compilation and computation

Obviously, the two lineage‐based assemblagemetrics are particu‐larlyaffectedbyincompleteorinaccuratetaxonomicandphyloge‐neticknowledge.However,keepingtrackofallnewinformationonthe systematics of diverse island assemblages is time‐consuming,andfutureimplementationsmightconsidercompilingandprocess‐ing automatically the spectra frommachine‐accessible databases.Suchasystemmightconstructalistofspeciesmakingupanassem‐blage, inputting it in theTToL, and then extract a time‐calibratedtree containing the listed species aswell as their sister groups. Ina second step, the requested metrics characterizing phylogeneticdiversity of island lineageswould be computed from this tree. At

     |  2747ALI And VEnCES

present, however, the database (accessed in February 2019) con‐tainsrecordsforonlyc.100,000species,which is justover1%ofEarth'sestimatedtotal(c.8.7×106;Mora,Tittensor,Adl,Simpson,&Worm,2011).SpeciesrepresentationismorecompleteinboththeOpenTreeofLife(Hinchliffetal.,2015)andOneZoomTreeofLifeExplorer(Rosindell&Harmon,2012),buttherespectivetreeslackdivergencedate information.However, these treescouldbeused,asafirststep,toidentifythenearestrelativesofanislandspecies,before proceeding with further computations based on the TToLdatabase.Distributionaldataoftherespectivelineagescouldthenbe retrieved from theMap of Life database (Jetz, McPherson, &Guralnick,2012). Ina futureofbigdataandmachine‐learningap‐plications, it is inevitablethattoolswillbecomeavailabletocalcu‐lateALTSandALAStypemetricsforislandbiota,andindeedforanycommunityassemblage.

10  | CONCLUSIONS

Twoparallelschemes,ALTSandALAS,havebeendevelopedthaten‐ablethebioticassemblagesonmarineislandstobesummarizedinawaythat reflects thegeo‐physicalsettingandgeologicalevolutionofthesubstrates.InthefavouredALTSsystem,thelineagesthatarepresentonaninsularlandmasscanbeassignedtooneofsixcatego‐ries(LT1‒LT6)usingtaxonomyasaproxyfortheirevolutionarymatu‐rity,LT1beinganativespeciesthatisalsopresentonthemainland,LT6comprisingtwoormoreendemicgenerathathavespawnedmul‐tiplespecies.Anisland'ssuitecanbeencapsulatedusingastraight‐forwardnumericalspectrum,forexampletheamphibiansonTaiwanarecoded52:32:16:00:00:00[19].Here,52%ofthelineagesusedintheanalysisareLT1,32%areLT2,16%areLT3,etc.Thelastnumber,19, indicatesthetotalnumberofprocessed lineages.Furthermore,thedatacanbeplottedgraphically:weprefercolour‐coded,stackedbarcharts.AscanbeseenfromFigure4,thesuitesontheproximalislandsofHainanandTaiwanaremarkedlydifferenttothoseontheolderandmoreremoteislands/platformsofNewCaledoniaandtheSeychelles.

Onindividualislands,differentfaunalgroupsmayexhibitdissimilarspectraillustratinginherentdifferencesintheirbiology.Thespectrumapproachthushasthepotentialtocharacterizethosefeatures.

Shortcomingsof theALTSmethod include taxonomicuncer‐tainty and the non‐equivalence of taxa since the various ranksunderpinthescheme;ALAScircumventstheseproblems.Ontheother hand, it is unlikely that complete dated phylogenies formany groups of organisms, for example, species‐rich arthropodclades,willbecomeanytimesoon;thereforeweseeameritfortheALTSmetricfordecadestocome.OtherissuesaffectingALTSandALASconcernextirpatedforms,invasivespecies,andtheam‐biguities related to the sourceof a lineage, especially for thosearchipelagoswhere overwater dispersal has occurred regularly.Regardless of these limitations, we suggest that the two alliedsystems will prove useful for summarizing the biotic suites onmanymarineislands.

TheALTSandALASmethodsmayalso informbiogeographicalstudiesofotherinsularsystemssuchaslakesandmountains,aswellaspalaeogeographicalmodelling.Additionally,theycouldbeuseful(anddevelopedfurther)forconservationefforts,particularlythoseassociatedwithislandswithdistinctive(LT4andhigher)and/oroldcomponents,astheyconveythesignificanceofanisland'sbiotainasimple,conciseway.

ACKNOWLEDG EMENTS

JonathanAitchison,ClaudiaCorti,BlairHedges,AndréKoch,SylvieLeroyandMarkO'Sheaarethankedforsharinginformation.Sun‐YiAliandEricaLeekindlycheckedvarious island‐areaestimates.Discussions with Mark Carine, Peter Linder and Hanno Schäferconcerningalternativestoataxonomy‐basedassemblagespectrumsystem proved very useful. Formal critiques provided by variousreviewershelpedustoimprovethemanuscript.Thestudywasinpartsupportedbya2018HKUFacultyofScienceEUtravelaward.

DATA AVAIL ABILIT Y S TATEMENT

Thevariousislandassemblageexamplesusedinthisworkdrawuponalreadypublisheddata. The associated literature is fully cited; re‐latedqueriesshouldbedirectedtoJRA.

ORCID

Jason R. Ali https://orcid.org/0000‐0002‐5214‐620X

Miguel Vences https://orcid.org/0000‐0003‐0747‐0817

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BIOSKE TCHE S

Jason R. AliisanEarthscientistattheUniversityofHongKong.Hehasspent30yearsworkingonvariousregional‐scalegeologicalinvestigations.Aboutadecadeago,hewasdrawntoMesozoic–Cenozoic biogeography, in particular how various geo‐physicalprocesseshaveshaped thedistributionsof the land‐lockedani‐mals.Hisresearchnowfocusesalmostexclusivelyonthistopic.Miguel Vences is a zoologist and evolutionary biologist atBraunschweig University of Technology, Germany. He leadsa long‐standing research program on the vertebrate fauna ofMadagascar,mainlytheamphibiansandreptiles,withtheinves‐tigations spanningclassical taxonomy,molecularevolution,di‐versificationprocesses,biogeographyandconservationbiology.Morerecently,hehasworkedontheGalápagossystem.

How to cite this article:AliJR,VencesM.Novelsummarymetricsforinsularbioticassemblagesbasedontaxonomyandphylogeny:Biogeographical,palaeogeographicalandpossibleconservationalapplications.J Biogeogr. 2019;46: 2735–2751. https://doi.org/10.1111/jbi.13706