Metapopulation vicariance explains old endemics on young ... · Metapopulations can be ruptured by...

Metapopulation vicariance explains old endemics on young volcanicislands

Michael Heads

Buffalo Museum of Science 1020 Humboldt Parkway Buffalo NY 14211-1293 USA

Accepted 20 March 2017

Abstract

Terrestrial plants and animals on oceanic islands occupy zones of volcanism found at intraplate localities and along island arcsat subduction zones The organisms often survive as metapopulations or populations of separate sub-populations connected bydispersal Although the individual islands and their local subpopulations are ephemeral and unstable the ecosystem dynamismenables metapopulations to persist in a region more or less in situ for periods of up to tens of millions of years As well as sur-viving on systems of young volcanic islands metapopulations can also evolve there tectonic changes can break up widespreadinsular metapopulations and produce endemics restricted to fewer islands or even a single island These processes explain thepresence of old endemic clades on young islands which is often reported in molecular clock studies and the many distributionpatterns in island life that are spatially correlated with tectonic features Metapopulations can be ruptured by sea floor subsi-dence and this occurs with volcanic loading in zones of active volcanism and with sea floor cooling following its production atmid-ocean ridges Metapopulation vicariance will also result if an active zone of volcanism is rifted apart This can be caused bythe migration of an arc (by slab rollback) away from a continent or from another subduction zone by the offset of an arc attransform faults and by sea floor spreading at mid-ocean ridges These mechanisms are illustrated with examples from islands inthe Caribbean and the Pacific Endemism on oceanic islands has usually been attributed to chance long-distance dispersal butthe processes discussed here will generate endemism on young volcanic islands by vicariancecopy The Willi Hennig Society 2017

Introduction

ldquoPlate tectonics perhaps more than any other phenomenon

has had profound effects on the biogeographic patterns of

both terrestrial and marine biotasrdquo (Lomolino et al 2010

p 306)

For many years biologists assumed that plant andanimal taxa attained their distributions by physicalmovement away from a centre of origin Until the1970s few authors accepted that vicariancemdashthe subdi-vision of widespread ancestral biotasmdashcould generatediverse widespread clades Instead most biologistsargued that barriers acted to isolate clades because ofthe rarity of chance dispersal across them not by theformation of the barriers themselves (review in Ebachand Williams 2016)

Vicariance became more widely accepted throughthe 1970s and 1980s but many biogeographersassumed that it could operate only on continents asthe result of continental breakup or the uplift ofmountain ranges Now in the molecular era mostauthors accept that vicariance occurs in many differentgeographical contexts and at a wide range of scalesHowever vicariance is still not accepted as an explana-tion for the classic exemplars of evolutionmdashendemicland organisms on young volcanic islands andarchipelagos This paper suggests several ways inwhich vicariance could account for these

Metapopulation theory

Most species whether on continents or islands havedistributions that are patchy and located in discontinu-ous areas of suitable habitat These species each exist

Corresponding authorE-mail address mjheadsgmailcom

CladisticsCladistics (2017) 1ndash20

101111cla12204

copy The Willi Hennig Society 2017

as a metapopulation that is a population of distinctsub-populations that are separated geographically butconnected by dispersalIndividual habitat islands and their populations are

often ephemeral Yet the constant production of newhabitat islands can lead to long-term survival of thespecies depending on the balance between local extinc-tions and recolonizations in the patchwork of frag-mented landscape (Hanski 1999) The process permitsldquothe metapopulation persistence of unstable but moreor less independently fluctuating local populationsrdquo(Hanski 1999 p 11)This model provides a good description of the popu-

lation dynamics in many species that inhabit activevolcanic archipelagos Metapopulations persist therethrough constant colonization of younger activeislands from older extinct ones and the latter eventu-ally subside Volcanic islands are short-lived in geolog-ical time but the volcanic centres that generate themare much older Most archipelagos in the central Paci-fic for example have been active for tens of millionsof years although their current islands are all muchyounger than thisThe metapopulation model explains how a group

can survive in a dynamic region In addition activevolcanic centres are often rifted apart into separateactive sections (eg at subduction zones offset bytransform faults) and so it is likely that the popula-tions there can also differentiate If an active volcanicarchipelago hosting a metapopulation is divided intoseparate active segments moving away from eachother the genetic cohesion of the metapopulation willbe reduced and eventually fail and vicariance into twoor more metapopulations can result Thus tectonicchanges including those discussed below can breakup widespread insular metapopulations and produceendemics restricted to fewer islands or even a singleisland Many regional zones of oceanic volcanism havebeen rifted apart and so clades endemic to young vol-canic islands there are likely to originate by vicarianceof widespread ancestors For example a group inhab-iting young volcanic islands in western Polynesia andits sister group with similar ecology in eastern Polyne-sia could both be derived from a widespread Pacificgroup that has been ruptured by sea floor spreading atthe East Pacific Rise Molecular phylogenetic studiesare documenting a growing number of such patternswith precise allopatry among terrestrial insular cladesthat each occupy a large sector of the Pacific (Heads2012 2014) and these could be the result of simplevicariance in an oceanic settingThis ldquometapopulation vicariancerdquo model of island

biogeography differs from the standard one in the sig-nificance attached to former islands In traditional the-ory these act as ldquohalting-placesrdquo or ldquostepping stonesrdquothat facilitate migration of rare individuals from a

continent to a distant island In contrast the metapop-ulation model proposes that the sequential emergenceof past present and future islands allows a metapopu-lation to survive in its particular region more or lessin situ and so it is not necessary to assume that thegroups have dispersed there from a continent In the-ory a lineage can persist in an insular region more orless indefinitely for as long as new islands are beingproduced

Earlier theories of island biogeography

The ldquoequilibrium theory of island biogeographyrdquo

Island biogeography has been explained in severalways The best known is MacArthur and Wilsonrsquos(1967) ldquoequilibrium theory of island biogeographyrdquoThis proposed that the two main processes determin-ing an islandrsquos biota were dispersal from the nearestmainland and extinction of groups on the island Vari-ation in these processes was in turn attributed to theislandrsquos area and its distance from the mainland Thetheory did not consider the islandrsquos specific location onthe Earthrsquos surface or the tectonic history of the vol-canic centre that produced the islandMacArthur and Wilsonrsquos (1967) model is still widely

accepted For example one illustrated scenario for anew volcanic island began with a large blank spacelabelled ldquoNothingrdquo (Gillespie and Roderick 2002fig 1) In this scenario the site has no geographicallocation and in particular no tectonic contextAlthough MacArthur and Wilson (1967) assumed

that mainland-to-island dispersal is a key factor deter-mining island biota ldquomigration among the islands isignoredrdquo (Hanski 2010 p 189) Yet migration amongneighbouring islands is a common process and it isprobably critical for evolution This is not because itleads to speciation but because it allows thepersistence of metapopulations more or less in situ forexample in the region occupied by a singlearchipelago

The ldquogeneral dynamic model (GDM) of oceanic islandbiogeographyrdquo

A recent model of oceanic island biogeography rep-resents an advance over the ecological approach ofMacArthur and Wilson (1967) as it incorporates thegeological ldquolife cyclerdquo of a volcanic island from smallto large and then small again (Whittaker et al 20082010) ldquoThe general dynamic model of oceanic islandbiogeography (GDM) has added a new dimension totheoretical island biogeography in recognizing thatgeological processes are key drivers of the evolutionaryprocesses of diversification and extinction within

2 Michael Heads Cladistics 0 (2017) 1ndash20

remote islandsrdquo (Borregaard et al 2017 p 830 italicsadded) This general approach is advocated here Stud-ies in comparative biogeography have often integratedgeological and biological data for example in analysesof old taxa endemic on young islands (Heads 2011)A detailed review of the GDM by Borregaard et al

(2017) only mentioned metapopulations once ldquoconnec-tivity serves to reduce extinction rates by facilitatingmetapopulation dynamicsrdquo (p 839) But connectivityimplies other processes in addition to simple survivalfor example what happens if the connectivity in anactive archipelago changes The GDM is not yet gen-eral or dynamic enough to answer this question itdoes not incorporate the tectonic changes that cantake place in an active archipelago and so it overlooksthe metapopulation vicariance that this is likely tocause Although it represents an advance over theequilibrium theory of island biogeography the GDMstill only considers geological evolution at the spatialand chronological scale of an individual island ldquoThecritical parameter for establishing the timescales ofbiological evolution on oceanic islands is the age ofemergence of an island rdquo (Triantis et al 2016 p2) In fact however as Triantis et al (2016 p 3) alsowrote ldquothe current geography of the archipelago maybe misleading of the configuration(s) relevant tounderstanding the evolutionary assemblage processes most archipelagos are older than the oldest extantisland rdquo This important principle of dynamic tec-tonic development also explains the fact that manyisland endemics are much older than their currentisland (Heads 2011)Borregaard et al (2017) supported the notion that

ldquothe spatial arrangement of islands within an archipe-lago and how this changes over time may have animportant influence on gene flow and differentiationwithin archipelagos rdquo (p 3 italics added) Yet intheir section on ldquoarchipelago dynamicsrdquo they referredonly to the rise and subsidence of individual islandsto whether or not islands have ever been conjoinedand to Pleistocene sea level change In fact volcanicarchipelagos can undergo a wide range of tectonicchanges these include subsidence with sea floor cool-ing and with volcanic loading and rifting of subduc-tion zones and intraplate volcanic centres at transformfaults and spreading ridges

Geology of oceanic islands

A small number of oceanic islands such as Mac-quarie Island south of New Zealand are tectonic inorigin and represent upfaulted sea floor but mostoceanic islands are formed by volcanism Volcanicislands do not develop at random sites but at volcaniccentres of different kinds These occur along active

plate margins where volcanism might be expected butthey are also found far from plate margins at intra-plate localities Both kinds of centres usually producemultiple islands over long periods of time and theyare older than the individual islands

Plate margin volcanism

Volcanic arcs along subduction zones can occur incontinental crust for example along the Andes or inoceanic crust for example in the Lesser Antilles andMelanesia Andesite (named after the Andes) is a typi-cal feature of subduction zones and the volcanic arcsthat they produce whether in continental or oceanicsettings In intraplate settings volcanic islands oftenform linear chains and are instead composed of alkalibasalts (oceanic island basalt) Normal sea floor crustproduced at mid-ocean spreading ridges (and also ter-restrial flood basalt) is tholeiitic basalt

Intraplate volcanism

The causes of intraplate volcanism are the subject ofcurrent debate (Foulger et al 2013) In the traditionalmodel intraplate volcanism develops above a hot nar-row deep mantle plume but the tomographic evidencecan be interpreted in different ways Also some linesof intraplate volcanics such as the Cameroon VolcanicLine do not show a simple linear sequence in the agesof the individual volcanoes In some regions such asthe eastern South Island New Zealand volcanism haspersisted in the same area for long periods eventhough the plate has moved and the South Islandwould have moved away from a mantle plume hot-spot French Polynesia contains five major volcanicchains with each attributed ldquosometimes with greatdifficultyrdquo to the drift of the Pacific plate over hot-spots (Bonneville 2009 p 339) The chain in the Mar-quesas Islands deviates 20ndash30deg from the direction ofthe absolute plate motion and this deviation is ldquoquiteoddrdquo (Bonneville 2009 p 342) The CookndashAustralisland chain has age distributions that are ldquoparticularlydifficult to resolve based on the hotspot hypothesis [there is] a wide geographic range of recent [and older]volcanismrdquo (Rose and Koppers 2014 p 1)To deal with these problems some geologists have

suggested complex ad hoc hypotheses such as multiplehotspots in an area hotspots that turn on and offand hotspots that move Other geologists have rejectedmantle plumes in the traditional sense as a cause ofintraplate volcanism and instead they have proposedmechanisms based on plate tectonics effects in thecrust (Smith 2007 Anderson 2010 Hamilton 2011)Propagating fissures in the crust caused by flexing andextension rather than mantle plumes could explainlines of volcanism in which the individual volcanoes

Michael Heads Cladistics 0 (2017) 1ndash20 3

along the line follow a simple age sequence and alsolines of volcanism without an age sequence

Metapopulations and volcanism

Outside a few specific localities notably Hawaii theconcept of metapopulations is seldom related to ocea-nic island volcanism Standard texts on metapopula-tions (eg Gilpin and Hanski 1997 Hanski 19992010 Hanski and Gaggiotti 2004) make little refer-ence to volcanism In one leading textbook on islandbiogeography the section on metapopulations (inChapter 10) does not mention volcanism while thesection on volcanism (in Chapter 2) does not mentionmetapopulations (Whittaker and Fernandez-Palacios2007)This neglect is probably because the usual concept

of metapopulations as adopted by many authorsspans only ecological timescales in metapopulationsldquothe timescale of their dynamics may be of theorder of decadesrdquo (Whittaker and Fernandez-Palacios2007 p 263) However metapopulations also have abiogeographical and geological context and they maypersist for tens of millions of years For example inmolecular clock studies the frog Leiopelma hochstetteriendemic to the New Zealand archipelago has beendated as Cretaceous (67 Ma Carr et al 2015)

Molecular evidence for metapopulation dynamics oldtaxa endemic to young volcanic islands and mountains

Groups that exist as endemic metapopulations atvolcanic centres can be much older than the individualislands themselves This principle has become morewidely accepted following the publication of molecularclock dates Fossil-calibrated clock dates give mini-mum clade ages and these show that many clades areolder than the islands they are endemic to (Heads2011) The results suggest that a young island couldhave been populated by endemics from nearby olderislands that later sank below sea level leaving thegroups endemic to the young island As long as newvolcanic islands are being produced the plants andanimals in the region can survive by a process of per-petual hopscotchSome young islands with endemics dated as older

were listed earlier (Heads 2011) and additional casesare constantly being reported For example a clade ofMalvaceae (ldquoClade Ardquo) endemic to Mauritius andReunion in the Mascarenes was dated as much olderthan the current islands (Le Pechon et al 2015) Theauthors wrote that ldquoTraditional interpretations ofinsular radiations often assume that endemic taxa radi-ated after the origin of the insular habitats on whichthey were established rdquo (p 211) In contrast the

authors concluded ldquoThe clade A pattern of old taxaon young islands indicates diversification before theformation of the Mascarenes and this characteristic isinconsistent with traditional scenarios of insular diversi-fication rdquo (p 218 italics added) The origin of cladeA was probably related to prior tectonic events thataffected former islands in the Mascarenes region (Ash-wal et al 2017)

Extinction on subsiding islands

Metapopulations of terrestrial organisms can survivein a zone of oceanic island volcanism for as long asthis is active If the centre becomes inactive the popu-lations there will go extinct one by one as the islandserode and subside and no new ones are formedBiological evidence for this sort of extinction includesfossil material of high island organisms such aswet-forest landsnails on what are now low sparselyvegetated atollsmdashformer high islandsmdashin the Pacific(Heads 2012 p 280) A small number of organismscan survive the harsh atoll environment and these willpersist in the region for much longer

Metapopulation survival in oceanic island systems

Metapopulation survival on single volcanic edifices

De novo volcanic edifices occur as islands in theocean basins and as habitat islands in continental set-tings As Darwin (1859 p 380) observed ldquoA moun-tain is an island on the landrdquo Belts of volcanism oncontinents include arcs (as in the Andes) and rift zones(as in the East African ldquoarcrdquo mountains) Endemics onthe volcanoes include species that are dated as olderthan the individual volcano they inhabit an exampleis the cricket Monticolaria kilimandjarica endemic onKilimanjaro by the Great Rift Valley (Heads 2012p 71) One explanation is that communities have sur-vived more or less in situ by small-scale metapopula-tion dynamics as the separate eruptions do not coverthe whole mountain at any one time New lava andash is colonized as soon as it cools by organismsfrom neighbouring areas of older strata Later the col-onized areas can act in turn as sources for coloniza-tion of other newer deposits in the vicinity

Metapopulation survival at an intraplate volcanic centrethe Hawaiian Islands

The most-discussed case of intraplate island bio-geography is the Hawaiian archipelago One theoryaccepts that the Hawaiian biota has survived asmetapopulations the islands are thought to haveformed continuously as the plate moved over a mantle


plume and successive new islands have been colonizedby populations from older ones (Beverley and Wilson1985) In the Hawaiian chain the oldest high island(Kauai) formed at ~5 Ma and the oldest emergentisland (Kure atoll) at ~30 Ma but the oldest sub-merged seamount that has been dated Detroit Sea-mount near the north-western end of the chainformed at 81 Ma (Cretaceous) This provides a mini-mum age for the chain its actual age is unknown asthe rest of it has been subducted beneath AsiaTriantis et al (2016) accepted the metapopulation

model for oceanic islands and wrote ldquoWithin volcanicarchipelagos comprising islands of multiple geologicstages for the younger growing islands the nearbyolder islands are generally the dominant sources ofcolonizers Species may be dynamically colonizingand going extinct from islands within an archipelagobut the species presence ie the metapopulation at thearchipelago level is conservedrdquo (p 7 italics added)Triantis et al (2016) noted that the Hawaiian lobeli-

ads (Campanulaceae) had an origin ldquo13 million yearsago (more than twice the age of the current oldestlarge island) rdquo (p 5) The authors concluded ldquoun-derstanding diversity dynamics at the island or eventhe archipelagic level necessitates understanding of thedynamics at the meta-archipelagic regional level rdquo(p 6 italics added) This approach adopted here alsostresses the former high archipelagos around Hawaiisuch as the Musicians seamounts to the north and theatolls of the Line Islands to the southApart from the lobeliads several other Hawaiian

endemics have been dated as older than the presentislands of the archipelago These include the plantsHillebrandia (Begoniaceae sister of Begonia) Hespero-mannia (Asteraceae) and ldquoPeucedanumrdquo sandwicense(Apiaceae) (Heads 2012 Spalik et al 2014) Spaliket al (2014) observed that the existence of these oldlineages on a young island may be explained by theirsurvival on former islands in the Hawaiian chain oron other island groups in the region They may alsohave occurred on former island groups in the regionDispersal theorists have occasionally considered

dynamic metapopulation-style survival on young vol-canic islands but they have rejected it OrsquoGrady et al(2012 p 703) wrote ldquoit is a fantastical conjecture topropose that single metapopulations have existed per-petually rdquo No-one is suggesting they have existedfor all time but if volcanic centres are active for mil-lions or tens of millions of years as they often are itis likely that metapopulations in the same region arejust as oldOrsquoGrady et al (2012 p 703) wrote that ldquometapop-

ulation theory fails to explain how taxa may persistfor millions of years on terrestrial real estate that hasyet to exist Geologically most oceanic archipelagoshave formed intermittently with periodic lulls leaving

large evolutionary time between emergences [of anyislands]rdquo The authors cited just one example as evi-dence for this idea they wrote ldquoOur well‑supportedunderstanding of the geologic processes underlying[Hawaiian] island formation precludes the panbiogeo-graphic persistence of metapopulations in any realsenserdquo (p 703 italics added) But this glosses over akey problemmdashcalculating the heights of formerislandsMany biologists have accepted that in the Hawaiian

region ldquothere was a period between at least 33 and29 Ma in which no islands existed and distant colo-nization was thus crucial rdquo (Triantis et al 2016 p5) Nevertheless the heights of the former islands wereestimated from the present surface area of the volca-noes assuming a 7deg slope for subaerial lavas (Clague1996 Price and Clague 2002) There is a great poten-tial for error in these calculations and Clague (1996p 40) stressed that estimating the longevity of anisland ldquois far more complex and therefore far moreuncertain than estimating either the age or size of thevolcanoesrdquo Other authors have also noted that theresults are ldquofairly approximaterdquo (Whittaker andFernandez-Palacios 2007 p 30) In fact the methodconsiderably underestimates the heights of present vol-canoes and so it probably also underestimates theheights of past volcanoes (Table 1) Despite this theidea that there were no emergent Hawaiian islandsbetween 33 and 29 Ma is now well entrenched in theliterature and it forms the entire basis of the theorythat all Hawaiian groups (and the biotas of all othersimilar archipelagos) dispersed there Instead it islikely that terrestrial groups have existed in the regionsince the origin of the chain at some time before theorigin of the oldest dated seamount Detroit Sea-mount in the Cretaceous (81 Ma)OrsquoGrady et al (2012 p 704) criticised the idea of

ldquowidespread connectivity across the paleo‑Pacific viametapopulations inhabiting a series of Atlantean [iemythical] archipelagos because of lack of evidencefor intervening populations and suitable island habitatin the regionrdquo Yet they overlooked the geological

Table 1Actual heights of volcanoes on Maui and Hawaii and maximumheights predicted by Clague (1996)

VolcanoActualheight (m)

Clague (1996)estimateof height (m)

E Maui 3055 2180Kohala 1670 1740Hualalai 2521 1040M Kea 4205 3050M Loa 4170 3050Kilauea 1277 1040


evidence for prior land that was cited in the work theywere criticising (Heads 2012) Thousands of atolls andsubmerged flat-topped seamounts (guyots) occur onsubsided sea floor throughout the Pacific and all theseare former high islands Maps of the ocean floor arefar from complete and only ~15 000 out of possibly~200 000 seamounts more than 1 km in height havebeen mapped there are better topographic maps ofthe Moon and Mars (Heads 2012 p 326) Thus it isnot too surprising that in 2005 the nuclear submarineUSS San Francisco was involved in a fatal collisionwith an uncharted seamount south of GuamIn addition to the evidence for islands on unthick-

ened sea floor there is also good evidence for sub-aerial eruptions on the large igneous plateaus of thecentral Pacific and the volcanics include fossil woodin intercalated sedimentary strata

Metapopulation survival along active plate margins

Volcanism along a subduction zone will generatenew habitat and allow metapopulation survival for aslong as subduction continues (Fig 1) Many clades areendemic to these zones and survive there as ldquovolcano-weedsrdquo An example is the shrub Scaevola gracilis(Goodeniaceae) restricted to the Kermadec and TongaIslands north of New Zealand The active KermadecndashTonga Ridge lies over the Australia platePacific plateboundary In Tonga Eocene volcanics are exposed onlsquoEua but S gracilis is only known from youngerislands including Tofua in Tonga and Raoul Island inthe Kermadecs which are still active S gracilis is mostcommon on Raoul Island where it forms dense standson open pumice slopes in the main crater (Sykes1998)

The volcano-weed Scaevola gracilis appears to bewell adapted to life on a subduction zone and withinits sector of the margin has probably been colonizingnew volcanoes as they appeared for millions of yearsmuch longer than the age of any individual islandRaoul Island endemics include many species and evengenera including the terrestrial isopod genusOkeaninoscia (Schmalfuss 2003)Island formation along the KermadecndashTonga arc is

ongoing In 2015 volcanic eruptions in Tonga createda new island 17 km across and 100 m high betweenthe islands of Hunga Tonga and Hunga Harsquoapai Theisland was composed of ash and large rock fragmentsand the first visitors reported that ldquoThere are thou-sands of seabirdsmdashall kinds laying eggs on the islandrdquo(Telegraph 2015)

Physical contact between islands is not necessary formetapopulation vicariance

It is usually assumed that vicariance of terrestrialgroups can only take place in a continuous populationon an area of continuous land Thus because mostvolcanic islands have never been joined with any otherland it is inferred that their terrestrial endemics musthave been derived by dispersalGillespie and Roderick (2002) wrote that for island

systems the primary distinction is between ldquofragmentrdquoislands that were joined to other land in the past andldquodarwinianrdquo islands that formed de novo the latterldquohave never been in contact with the source of colo-nistsrdquo (p 595 italics added) This emphasis that bio-geographers have placed on physical contact hasobscured the importance of metapopulations thatinhabit unconnected islandsWhittaker and Fernandez-Palacios (2007 p 19) pro-

posed that a vicariance origin for an island biotarequires ldquothe breaking of a past land connectionrdquo Theauthors accepted vicariance as a possible mode of evo-lution on continental fragment islands such as Mada-gascar but ldquoFor true oceanic islands the startingpoint is different dispersal across a pre-existing bar-rierrdquo (Whittaker and Fernandez-Palacios 2007p 203) In situ speciation by vicariance is thusaccepted for differentiation within single islands andarchipelagos but it is ruled out for large oceanicregions such as west Pacific islands vs east Pacificislands or east Pacific islands vs AmericaThe suggestion that vicariance can only take place

within a single completely continuous population is apopular one but it appears to be flawed Most speciesand presumably most ancestors have patchy distribu-tions with separate populations connected by normalecological dispersal This dispersal occurs for examplebetween populations located in different parts of one

= Past and future volcanic islands= Present volcanic islands with populations

Time 1

Time 2

Trench

Arc

Fig 1 Survival of a metapopulation along the island arc of anactive subduction zone The barbed line indicates the trench withthe barbs on the over-riding plate Arrows indicate plate movementVolcanic arcs are located along subduction zones on the over-ridingplate ~200 km back from the trench


island and among populations on different neigh-bouring islands The process is not long-distance dis-persal in the sense of biogeographers as (i) it isobserved not inferred (ii) it involves the regularrepeated movement of many individuals or diasporesnot events that are rare or unique in geological timeand (iii) it does not lead to speciation or indeed anydifferentiation This ldquonormalrdquo dispersalmdashunlike long-distance dispersalmdashis a key process that needs to beincorporated in analysis not because it causes specia-tion (it does not) but because it enables metapopula-tion survival in a dynamic environmentAll individual organisms that establish anywhere

have dispersed from their point of origin across areasof land or water and if there are available sites themetapopulation will survive Whether the sites are con-nected by continuous land is irrelevant to the basicpopulation dynamics propagules of a species maycross a fence or a stream an area of land or a seawayas a regular part of the speciesrsquo ecology A metapopu-lation surviving in this way especially a widespreadone is likely to be polymorphic but if conditionsremain constant it will not differentiate into distinctnew speciesOrsquoGrady et al (2012) criticised the idea of metapopu-

lation vicariance in the central Pacific (Heads 2012)writing that it ldquoreally is not a theory at allrdquo becauseldquothe lack of any significant connections between theseremote islands and the mainland are ignoredrdquo (p 703)But this lack of connection is not ignored instead it isthe whole point of the metapopulation conceptmdashthesubpopulations are not connected by continuous suit-able habitat but they are connected by dispersal andgene flowIn rejecting the ldquopanbiogeographic persistence of

metapopulationsrdquo and its relevance for island biogeog-raphy dispersal theorists (OrsquoGrady et al 2012 p703) reject the normal overwater dispersal that isoften observed taking place over say tens of kilome-tres within archipelagos Yet at the same time disper-sal theory accepts that the biota of remote islandgroups such as Hawaii is derived entirely by long-dis-tance dispersal over thousands of kilometres The posi-tion seems untenable

Metapopulation vicariance in oceanic island systemstectonic mechanisms

Geological change in systems of oceanic islands

As Borregaard et al (2017 p 836) wrote ldquo thespatial arrangement of islands within an archipelagoand how this changes over time may have an importantinfluence on gene flow and differentiation within archi-pelagosrdquo (italics added) How exactly do changes in

the spatial arrangement of oceanic islands and archipe-lagos take placePleistocene sea level change is one obvious mecha-

nism and it is the only mode of vicariance amongislands that is accepted in dispersal theory For exam-ple for many years it was the usual explanation forclade distributions in the Philippines Yet most molec-ular studies of Philippines groups now agree that themodel is flawed This is because there is no spatialagreement between the main patterns of clade distribu-tions and the geography of the Pleistocene islands andbecause the minimum clade ages calculated in clockstudies are older than the Pleistocene (Heads 2014chapter 10) The new molecular evidence suggests thatthe events in Earth history that are relevant for evolu-tion in the Philippines were tectonic in origin and pre-Pleistocene in ageIn oceanic environments vicariance of terrestrial

and reef metapopulations would be expected to accom-pany particular types of tectonic change in the crustthat are well documented at plate margins and intra-plate volcanic centres The next sections deal withsome of these processes

Vicariance caused by volcanic loading and subsidence

The growth of oceanic islands by repeated eruptionsis often followed by subsidence of the edifices causedby the weight of the rocksmdashvolcanic loadingmdashand iso-stasy These processes ldquohave reiteratively mixed andisolated populations creating a mechanism for vicari-ant speciationrdquo (Triantis et al 2016 p 3) The Hawai-ian Islands provide good examples of vicarianceprobably caused by subsidence and the process isoften accepted for islands in the group that were oncejoined Borregaard et al (2017 p 836) stressed thatldquoOrsquoahu was in the past briefly conjoined to Molokarsquoiwhich then became conjoined with Lanarsquoi Maui andKahorsquoolawe to form Maui Nui although they arecurrently separate islandsrdquo (italics added)However as stressed already islands do not have to

be conjoined and then separated for metapopulationvicariance to occur If islands that were never con-nected are close enough for normal dispersal to occurbetween them ancestral forms can exist as metapopu-lations If the distance between the islands then in-creases with subsidence vicariance can developbetween the islands The former metapopulation canthen evolve into endemics restricted to fewer islands orto single islandsFor example several groups in the Hawaiian archi-

pelago display a break between a clade on Hawaiiisland and its sister-group on the other islands (reviewin Heads 2012 p 366) Hawaii and its nearest neigh-bour Maui were originally 8 km apart but followingvolcanic loading they are now 50 km apart Organisms


that can disperse 8 km and maintain a metapopulationare not necessarily able to disperse 50 km and so formany groups vicariance would result This mode ofspeciation does not seem to have been discussed forHawaiian taxa

Vicariance caused by sea floor cooling and subsidence

As sea floor drifts away from the spreading ridgethat is producing it it cools (increasing its density)over tens of millions of years and subsides by largeamounts (van der Pluijm and Marshak 2004) Thisleads to the submergence of many islands that haddeveloped on it earlier most current high islands onolder oceanic crust such as the Hawaiian group arenew ones Modern dispersal models for oceanic islandseither do not acknowledge this massive subsidence(eg Cantley et al 2016) or even reject it (OrsquoGradyet al 2012) but it is another likely cause of breaks inmetapopulations on groups of oceanic islandsOne recent analysis of the Hawaiian Islands biota

stressed the former islands in the central Pacific thatare now submerged and it mapped the 2000- 4000-and 5000-m isobaths in the region (Heads 2012figs 7-1 7-2) Yet Holland (2012 p 146) wrote thatldquothe figures appear to be a disingenuous and mislead-ing depiction aimed at advancing the vicariantagendardquo OrsquoGrady et al (2012 p 704) agreed that thefigures were ldquomore than slightly disingenuousrdquo as sealevel has not dropped by more than ~100 m and sothe many submerged seamounts could not have beenemergent Nevertheless all these authors overlookedthe thousands of metres of subsidence that the Pacificsea floor itself has undergone through the Cenozoic(van der Pluijm and Marshak 2004 p 404 Hillierand Watts 2005 Zhong et al 2007 fig 1)

Vicariance caused by migration of an arc away from acontinent

Biogeographers are well aware that the two platesconverging at an active subduction zone are mobilebut they often neglect the fact that subduction zonesthemselves along with their associated arcs can alsomove Usually the trench marking the subduction zoneretreats towards the subducting plate The processtakes place by slab rollback with the descending slabof crust falling backwards even though its plate ismoving forwards as in a retreating wave on aseashoreSlab rollback can lead for example to the migration

of a volcanic arc away from the edge of a continentand far into the ocean This is another way in which ametapopulation can be subdivided (Fig 2) There isno fundamental difference between a metapopulationon a drifting island arc and one on a drifting

continent In both cases the organisms survive by dis-persal among suitable habitat patches whether theseare new islands in an arc or for example new moun-tains on a continentSlab rollback is thought to be a fundamental process

in the development of the south-west Pacific (Fig 3)The history there over the last 200 Myr has been dom-inated by the following processes

1 Accretion of oceanic terranes (including sea-mounts and island arcs) from the pre-Pacific onto con-tinental crust with associated uplift2 Pre-drift rifting and magmatism (from ~100 Ma

to 80 Ma)3 Gondwana breakup with sea-floor spreading4 Migration of the main Pacific subduction zone

and its island arc by slab rollback into the Pacific(~90 Ma onwards) So far the subduction zone hasmigrated as far east as TongandashKermadec IslandsndashNewZealand As the arc migrated eastward a series ofbackarc basins including the Tasman and Coral Seabasins opened behind it (Backarc basins are localizeddivergent rifts but are formed in zones of overall plateconvergence) Some of the basins opened in the conti-nental crust of Gondwana and caused its breakup(Fig 3) Some of the backarc basins notably theSouth Loyalty basin opened but then later closed5 Development and migration of other subduction

zones behind the first belt (Fig 3)

These processes all led to profound geographicalchanges that are likely to have caused vicariance forexample in widespread Pacific and Indo-Pacific ances-torsThe neglect of slab rollback in biological work has

led to problems in dating studies For example astudy of Fijian taxa calibrated a phylogeny using asuggested age of Kadavu Island in southern Fiji (15ndash25 Ma) to date endemics there (Monaghan et al2006) The geological age was based on the age ofexposed volcanic strata on the island These stratabelong to the current phase of volcanism in whichocean island basalts (typical of intraplate volcanism)have been erupted and emplaced over earlier rocksNevertheless before the latest volcanism a prior arc

passed through Fiji (the extinct trench ldquo1rdquo in Fig 3)and instead produced andesites typical of subductionzones Exposed rocks of this earlier phase are datedfrom the Eocene to Miocene (Colley and Hindle 1984Cronin et al 2003)Yet the history of volcanism in the antecedents of the

Fijian archipelago probably goes back even furtherRegional tectonic models propose that the subductionzone and its island arc date back to the Cretaceouswhen the ancestral arc migrated away from the proto-Australian part of Gondwana (Fig 3) This slab roll-back and the long history of earlier islands is probably


more important for the biogeographical history of Fijithan the age of the current islandsThe SW Pacific sea floor includes many ridges with

distinctive linear morphology These can represent rib-bons of continental crust (Norfolk Ridge Lord HoweRise in Fig 3) arcs at subduction zones (LoyaltyndashThree Kings LaundashColville TongandashKermadec inFig 3) or mid-ocean spreading ridges (none areshown in Fig 3)

Vicariance caused by the lengthwise splitting of anactive subduction zone with one active arc separatingfrom another

One tectonic model for the TasmanndashCoral Sea regionproposes three sets of subduction zones (Fig 3 simpli-fied from Schellart et al 2006) As the primary subduc-tion zone migrated eastward into the Pacific secondaryand tertiary arcs developed behind it The secondarysubduction zones differed from the first in their subduc-tion polarity and they underwent westward rollback

In one example of this from 50 to 25 Ma the Loy-alty IslandsndashThree Kings subduction zone and its arc(labelled ldquo2rdquo in Fig 3) split off from the initial Pacificsubduction zone (labelled ldquo1rdquo in Fig 3) (Note that anarc is typically located ~200 km behind its associatedtrench) Westward rollback of the new arc pulled theLoyalty Islands ridge (now part of the New Caledoniaarchipelago) away from proto-Vanuatu until eventu-ally it collided with the continental crust of mainlandNew Caledonia and Norfolk Ridge At this point sub-duction at the trench and volcanism along the arc bothceasedThis tectonic history would explain the great biolog-

ical difference between the Loyalty Islands and thenearby mainland of New Caledonia which is other-wise enigmatic It would also explain the great similar-ity of the Loyalty Islands with the more distantVanuatu (Heads 2008) As the new Loyalty arcformed it would have been colonized from the adja-cent primary Pacific arc but with continued slab roll-back the biotas of the two arcs have diverged

Continental hinterland with lsquoislandsrsquo of suitable habitat (gray)

Volcanic arc along continental margin with lsquoislandsrsquo of suitable habitat (gray)

Openingof backarc basin

New continental margin with lsquoislandsrsquo ofsuitable habitat(gray)

New island arc with volcanic islands(gray)

= Past and future islandshabitat islands

Trench rollback

Time 1 Time 2

= Present volcanic islandshabitat islands with populations

Continental margin Trench

Fig 2 Migration of a subduction zone and its arc away from a continent by slab rollback


WestAntarctica

Australia

HikurangiPlateau

Antarctica

Australia

HikurangiPlateau

Australia

HikurangiPlateau

Australia

90 Ma

75 Ma

50 Ma

60 Ma

Australia

45 Ma

Australia

35 Ma

12

12

2

BT

T

CSBCSB

SLSL

NC

2

LT

VTKNL

2 1

NRLHR

VTKLT

East Ant- arctica

East Ant- arctica

SLSL


Vicariance caused by the lengthwise splitting of anactive subduction zone with an active frontal arcseparating from a remnant arc

The opening of a backarc basin behind a migratingoceanic arc can separate one active island arc fromanother in which subduction and volcanism cease Forexample at ~15ndash10 Ma the Ontong Java Plateau andthe Melanesian Border Plateau arrived from the Pacific

at the Vitiaz trench section of the Pacific plate subduc-tion zone These are large igneous plateaus and theirarrival blocked subduction along the Vitiaz trench sub-duction then developed (with opposite polarity) alongthe trench at Vanuatu (labelled ldquo3rdquo in Fig 3) The newtrench propagated from the Bismarck Archipelago tothe Solomon Islands Vanuatu and FijiIn this case the VanuatundashFiji section of the primary

arc (at the Vitiaz trench) has been left inactive The

Australia

15 Ma

Australia

10 Ma

Australia

5 Ma

Australia

Present

12

33

2

1

1

2 3

2

3

1

23

NFLL

LCTKTK

LC

Fig 3 Continued

Fig 3 Tectonic reconstruction of the south-west Pacific from the Late Cretaceous to the Present The reference frame is Australia-fixed Lightgrey = continental crust and island arc crust dark grey = oceanic plateaus Geographical outlines are shown to help identify the location of the crus-tal blocks but have no palaeogeographical significance Arrows in the 90-Ma reconstruction = migration of subduction zone by slab rollback 1 23 = 1st 2nd and 3rd generation subduction zones BT Bounty Trough CSB Coral Sea Basin LC LaundashColville Ridge LHR Lord Howe Rise LTLoyaltyndashThree Kings Ridge NC New Caledonia Basin NL North Loyalty Basin NR Norfolk Ridge SL South Loyalty Basin T Tasman BasinTK TongandashKermadec Ridge NF North Fiji Basin VTK VitiazndashTongandashKermadec Ridge Simplified from Schellart et al (2006)


new arc (ldquo3rdquo in Fig 3) has probably inherited most ofits biota from the old oneAnother case concerns the Lau group of islands in

eastern Fiji (Fig 3 reconstruction for 5 Ma) The LauRidge is a remnant arc that has subsided but it is stillemergent in parts and maintains a distinctive biotaThis is known for its altitudinal anomalies includingotherwise montane species found near sea level on thesubsided islands (Heads 2006)The Lau Ridge dates as a separate feature to 6 Ma

when the TongandashKermadec arc (ldquoTKrdquo in Fig 3) onthe oceanic side began to separate from the LaundashCol-ville arc (ldquoLCrdquo in Fig 3) on the continental side andmigrate eastwards away from it The LaundashColville arcthen ceased activity Ever since the separation of theTonga arc a backarc basin (Lau Basin) has been

rapidly opening between it and the Lau ridge separat-ing the biotas of Tonga and the Lau group At thesame time the Fiji plateau has rotated anticlockwiseto meet the Lau ridge (Martin 2013)The close biogeographical connections that the Lau

group has with Tonga (rather than with western Fiji)are well known For example the landsnail Samoanaand the parrot Vini each have species on Lau Tongaand islands further east but do not occur west of Lauin the main Fijian islands (Heads 2012 fig 6-2 and6-11) This pattern is consistent with the tectonicdeformation that has taken place

Vicariance caused by the fracturing and offset ofsubduction zones at transform margins

Geologists classify plate boundaries into three mainkinds

1 Convergent margins These are marked by sub-duction zones and are usually associated with volcan-ism and uplift Most plate margin islands areproduced at subduction zones2 Divergent margins These are marked by spread-

ing centres which may be either mid-ocean ridges orcontinental rifts3 Transform margins (ldquotransformsrdquo) These are

marked by transform faults that display neither con-vergence nor divergence but connect convergent anddivergent margins (Fig 4)

Transform faults are strike-slip faults in which theplates slide past each other horizontally rather thanvertically Unlike most strike-slip faults transformfaults cut through the entire lithosphere and thus actas plate margins Transforms connecting two

Time 2

Fracture zone

Fracture zone

Transform margin

Time 1


Trench of active subduction zone

Island arc

Fig 4 Disjunction at a subduction zone (barbs on over-riding plate)caused by strike-slip displacement at a transform margin Note thelack of current strike-slip on the fracture zones and the lack of vol-canism along the transform

1

2

4 5 3

Caribbean plate

Toxostoma clade 1 (2 (3 (4 + 5)))

Fig 5 Distribution of a clade in Toxostoma (Mimidae) 1 = Tcurvirostre 2 = T ocellatum 3 = T rufum 4 = T guttatum 5 = Tlongirostre Phylogeny from Lovette et al (2012) distributions fromIUCN (2016) Continuous lines = divergent and transform platemargins Lines with barbs = subduction zones (barbs on over-ridingplate) Plate boundaries simplified


subduction zones can cut though continental crust (asat the Alpine fault in New Zealand the San Andreasfault in California and the southern margin of the

Caribbean plate) or through oceanic crust (as at thenorthern margin of the Caribbean plate)Active transform margins continue beyond their

junction with a convergent or divergent margin asfaults termed fracture zones (Fig 4) There is no cur-rent strike-slip displacement on the fracture zones asthe crustal blocks on each side (both part of the sameplate) are moving at the same speed and in the samedirection Active strike-slip is restricted to the trans-form (Fracture zones display evidence of past strike-slip however as the crustal blocks on opposite sidesof a fracture zone have different ages)Island arcs along convergent plate margins have

often been offset by displacement at transform faultsAt the time of the displacement metapopulations onthe island arc segments will also have been riftedapart and this would generate vicariance and ende-mism along the plate margin This provides a simpleexplanation for the 2600-km disjunction in the birdToxostoma (Mimidae) between Mexico (CozumelIsland) and the Lesser Antilles (Fig 5) The gap in therange can be explained by the displacement that hasoccurred along the northern and southern margins of

Vanuatu

NewCaledonia

New Caledonia

LauRidgeLau Ridge

TongaRidgeTonga Ridge

Loyalty Ridge

TongaTonga

SamoaMBP

SLBSLB

LB

NR

TavTav

LauLau

OJP

Vitiaz trench

Hunter fractu

rezo

ne

LHR

= 1 = 2 = 3 = 4 = 5 = 6

LoyLoy

Fiji fracture zone

SCSC

500 km

FijiFiji

180deg170deg

15deg

20deg

Fig 7 Tectonics of eastern Melanesia (after Schellart et al 2006 Martin 2013) 1 = Continental crust (LHR and NR) and arc crust2 = Oceanic plateau 3 = Active subduction zone (barbs on over-riding plate) 4 = Extinct subduction zone 5 = Mid-ocean spreading ridge6 = Normal (extensional) fault LB Lau Basin LHR Lord Howe Rise Loy Loyalty Islands MBP Melanesian Border Plateau NR NorfolkRidge OJP Ontong Java Plateau SC Santa Cruz Islands SLB South Loyalty Basin Tav Taveuni

Present

120 Ma120 Ma

1001008484

7171 5656 4646 33331919

1010

Fig 6 Former relative positions of the Caribbean Trench from120 Ma to the Present The base map has no palaeogeographical sig-nificance over the time period shown North and South Americahave drifted apart (Pindell and Kennan 2009)


the Caribbean plate (Fig 6) and passive transport ofthe bird populations The strike-slip has accommo-dated the eastward migration of the active Caribbeantrench with its arc the zone of volcanism has rolledback through mainland America to its present positionin the Lesser Antilles where it remains activeIn the SW Pacific there has been a complex history of

subduction zone development over the last 100 Myrand the belts are offset in many places by transformsThe island arc archipelagos of Vanuatu and Fiji providea good example (Fig 7) The two together form animportant centre of endemism that is well defined byabout 20 seed plant species or putative sister species (23if the Santa Cruz Islands are included with Vanuatu)(Smith 1979ndash1996) For example the palm Neoveitchiacomprises one species in Vanuatu and one in Fiji whileBalanops pedicellata (Balanopaceae) is a tree of uplandrainforest in the two archipelagos Several VanuatundashFijigroups are in Vanuatu only on the southern islands thepart of the archipelago that originally lay next to FijiThe VanuatundashFiji centre of endemism and its biota

have been rifted apart by the opening of the North Fijibasin along spreading ridges and transform marginsespecially the Hunter and Fiji fracture zones (Fig 7)Many groups in Vanuatu and Fiji would each haveexisted as metapopulations when the islands were adja-cent but the archipelagos and the metapopulationshave since been rifted apart by ~800 km of sea floorspreading Martin (2013) and Patriat et al (2015) pro-vided detailed reconstructions of the region showingFiji and Vanuatu rotating away from each other in thesame way that double saloon doors openAs discussed above the Lau group in eastern Fiji

was formerly adjacent to the Tonga arc and there arefive seed plants each endemic to Vanuatu Fiji andTonga (Smith 1979ndash1996) This suggests that each ofthe five species represents a disrupted metapopulationIn Vanuatu islands such as Tanna are currently being

built up by active volcanism while older islands havedisappeared in historical times by sliding down-slopeinto interarc rifts (Nunn et al 2006) In Fiji recent vol-canism (beginning at 08 Ma) has built the island ofTaveuni 1241 m high while 100 km to the south-eastin the remnant arc of the Lau group there has been con-siderable subsidence The distinctive montane endemicson Taveuni include the national flower tagimaucia(Medinilla waterhousei Melastomataceae) These ende-mics could have originated on the Lau group andcolonized Taveuni before subsidence of the Lau islandsled to the extinction of many higher-altitude groups there

Metapopulation vicariance of marine groups attransform faults

Deep-sea hydrothermal vents including black andwhite smokers are located at zones of magmatism

usually at mid-ocean ridges As with volcanic islandsthe vents are ephemeral features Nevertheless theorganisms found around the vents include local andregional endemics restricted to the habitat Theseinclude the giant tube worm Riftia that forms columnsup to 24 m tall and 4 cm wide Many authors haveaccepted that organisms at the vents can displaymetapopulation dynamics and that ancestral metapop-ulations on the mid-ocean ridges have undergonevicariance with displacement at transforms (Johnsonet al 2006 Plouviez et al 2009 Vrijenhoek 2010Moalic et al 2011) This research represents an excit-ing new synthesis of tectonics and marine biology Incontrast the possible effects of transforms on reefgroups and terrestrial groups in oceanic settingsremain unexploredDifferent oceanic groups of plants and animals

including volcano weeds and hydrothermal marinetaxa at the plate margins intertidal groups aroundoceanic islands and terrestrial groups on oceanicislands all differ in the details of their ecology Yetthey all share metapopulation dynamics and if theyare to survive all require active magmatism and itsproducts (such as hydrothermal vents shallow reefsand islands) Likewise groups in these different set-tings are all likely to undergo vicariance whenever thesubduction zones are ruptured by transform faults

Vicariance of oceanic metapopulations by sea floorspreading at mid-ocean ridges

Mid-ocean spreading ridges are divergent plate mar-gins and it is often accepted that they can causevicariance between continental biotas Yet their activityalso separates biotas of oceanic islands and archipela-gos as in the North Fiji Basin and the Lau BasinThis process has also taken place at a much largerscale in the Pacific Basin as a whole Its main spread-ing ridge the East Pacific Rise is generating the Paci-fic plate to its west and the Juan de Fuca CocosNazca and Antarctic plates to its east The sea floorspreading would explain disjunction in many groupsOne example comprises Fitchia + Oparanthus (Aster-aceae) of SE Polynesia and the pairrsquos sister Selleophy-tum + Narvalina of Hispaniola (Mort et al 2008Heads 2012 fig 6-15) Others include a clade of Fuch-sia (Onagraceae) in New Zealand and Tahiti and itssister in South America (Heads 2016 fig 103) andApostates (Asteracae) of Rapa Island and its sister theNew World Bahia group (Baldwin and Wood 2016)Apart from causing divergence between plates

spreading ridges can themselves migrate and themigrations of the East Pacific Rise and other spreadingridges in the Pacific are of particular significance forbiology For example a broad belt of mid-ocean ridgebasalts dated as Cretaceous extends for 7000 km from


Easter Island in SE Polynesia north-west to the Tua-motu PlateauAustral Islands Line Islands Mid-Paci-fic Mountains and Shatsky Rise (1500 km east ofJapan) (Samples from the oldest dated seamount inthe HawaiianndashEmperor chain the Detroit seamountalso show an isotopic signature indistinguishable fromthat of mid-ocean ridge basalt) This belt of on-ridgevolcanism surrounds the off-ridge intraplate volcan-ism of the Hawaiian chain and is likely to mark a for-mer position of the East Pacific Rise (Heads 2012fig 6-1)Tectonics in the Pacific can be summarized as fol-

lows The Pacific plate originated in the mid-Jurassicas a local feature near the modern Cook Islands at asite where three ridges met at a triple junction (Smith2007) (Although the precursor of the modern PacificOcean has grown smaller through the Cretaceous andCenozoic the Pacific plate along with its active mar-gins has expanded) One of the ridges at the triplejunction the East Pacific Rise has migrated east andeventually it collided with the western seaboard ofNorth America (which was migrating west) Through-out the eastward migration of the ridge the sea floorspreading taking place along it was probably animportant mode of metapopulation vicariance in theterrestrial and reef biotas of the Pacific islandsLarge-scale volcanism has persisted in the central

Pacific region since at least the Jurassic At that timethe oldest of the Pacific large igneous provinces theShatsky Rise began to be erupted in the regionnow occupied by French Polynesia Plate movement hastranslated this plateau to its present position in deep seaeast of Japan (Heads 2012 fig 6-1) The fossils andlithology at the plateau indicate shallow-water or sub-aerial volcanism during its emplacement (Sano et al2012) Following the eruption of the Shatsky Rise vol-canism continued in the central Pacific through the restof the Cretaceous and the Cenozoic

Dating clades

Vicariance is often rejected as a mode of differentia-tion between clades because the clades concerned arethought to be too young that is younger than the tec-tonic structures at their boundaries Yet the dates arecalibrated with fossil ages and without adding ad hocassumptions this can only give minimum ages forclades Actual clade ages are likely to be much older

Fossil calibration of Bayesian timetrees the problem ofthe priors

How much older than its oldest fossil can a groupbe In Bayesian analyses this amount is stipulated fora group before analysis as a ldquopriorrdquo and it is used to

calibrate the timetree Priors are not observed or evencalculated they are simply imposed they representldquoexpert knowledgerdquo and these ldquoprior-encoded beliefsvary from expert to expertrdquo (Landis 2017 p 129)Experts in the Modern Synthesis tradition haveassumed that a group is only a little older than its old-est fossil and modern Bayesian clock studies maintainthis view However there is no logical basis for itHow should priors be selected This is controversial

and ldquojudgement of the degree to which fossil minimaapproximate divergence timing could be considereda dark art rdquo (De Baets et al 2016 p 1) Naturallythe priors that are specified have a great effect on theresults ldquoErrors in the time prior and in the rate priorcan lead to very precise but grossly inaccurate time esti-mates rdquo (dos Reis et al 2016 p 74) Kumar andHedges (2016 p 863) wrote ldquowe feel an urgent needfor testing the accuracy and precision of third andfourth generation methods [for generating timetrees]including their robustness to misspecification of priorsin the analysis of large phylogenies and data setsrdquo Totest the priors and the fossil-calibrated timetrees theseneed to be compared with the results from anothermethod One other method of calibrating phylogeniesis discussed next

Tectonicndashbiogeographical calibration of timetrees

The tectonicndashbiogeographical method of datingclades correlates biogeographicalndashphylogenetic breakswith spatially coincident tectonic breaks For exampledifferentiation between a group endemic to Vanuatuand one in Fiji could be dated to the separation ofthe two archipelagos at ~10 Ma Differentiationbetween a group endemic to the main Pacific subduc-tion zone and a sister on mainland Australia could bedated to the separation of the arc from the continentin the Cretaceous (Fig 3) De Baets et al (2016 p 1)discussed the use of tectonic features to date cladesand wrote

ldquoFossils only really provide minimum clade age constraints

In their place phylogenetic trees can be calibrated by pre-

cisely dated geological events that have shaped biogeography

Biogeographic calibrations are no panacea for the short-

comings of fossil calibrations but their associated uncertain-

ties can be accommodated Biogeographic and fossil

calibrations are complementary not competing approaches

to constraining molecular clock analysesrdquo

Because the methods are independent it is possible tocompare and test fossil-calibrated clade ages againstbiogeography-calibrated agesThe standard view of evolutionary chronology

through the Phanerozoic is the fossil-calibrated time-line Despite this tectonic dating is now beginning tofind favour A recent review of evolution in the cab-bage family Brassicaceae concluded


ldquoWe suggest that the few known fossils require a critical re-

evaluation of phylogenetic and temporal assignments as a pre-

requisite for appropriate molecular dating analyses within the

family In addition (palaeo)biogeographical calibrations not

explored so far in the family should be integrated in a syn-

thesis of various dating approaches rdquo (Franzke et al

2016 p 554)

An analysis of New Zealand Brassicaceae using(palaeo)biogeographical calibrations is presented else-where (Heads 2016)Landis (2017 p 129) argued that ldquofossil-free calibra-

tion methods are desperately neededrdquo and he sup-ported the use of tectonicndashbiogeographical dating

ldquoMany major paleogeographical events are dated and since

biogeographic processes depend on paleogeographical condi-

tions biogeographic dating may be used as an alternative or

complementary method to fossil dating Biogeographic dat-

ing may present new opportunities for dating phylogenies for

fossil-poor clades since the technique requires no fossils This

establishes that historical biogeography has untapped practi-

cal use rdquo (pp 128 142)

Spatial coincidence between geological structures andbiological groups is widespread and so there are manyopportunities for testing tectonicndashbiogeographical cali-bration These include groups on young oceanic islandsAlthough Landis (2017) advocated testing tectonic

methods of dating clades Matzke (2015 p 328)argued that using vicariance events for dating ldquomakes[the] inference circularrdquo Nevertheless it is not circularto make an assumption (Heads 2016 p 61) Authorsusing fossil ages to date clades also make critical

assumptions (the Bayesian priors) about just howmuch older than its oldest fossil a clade can be

A case-study metapopulation vicariance in a continentaland oceanic group

The tribe Anthospermeae (Rubiaceae) has a south-ern distribution with the four main clades foundrespectively in South Africa (Carpacoce) Africa(Anthosperminae) Australia (Operculariinae) and thePacific (Coprosminae) The distribution and phylogenyare shown in Fig 8 The first three clades occur oncontinents while the last inhabits continental landsand islands in the west Pacific but also most of thehigh oceanic islands in the central and east PacificThe usual model of spatial evolution in the Anthos-

permeae proposes a centre of origin in Africa becauseof the paraphyletic basal grade there (Carpacoce andAnthosperminae) With respect to time Bayesianmolecular clock analyses using fossil calibrations andstipulating narrow priors gave clade ages that areyounger than the opening of the oceans (Wikstreuroomet al 2015) thus supporting trans-oceanic dispersalLikewise in the Pacific group Coprosminae Cantleyet al (2016) rejected a vicariance origin for the islandclades (including a VanuatundashFiji pair of sister species)as the current islands have never been joined to a con-tinent or to each otherAn alternative model for Anthospermeae proposes

that the four main clades evolved more or less in situ by

1

2

3

41 (2 (3 + 4))Anthospermeae

x

Fig 8 Distribution of tribe Anthospermeae (Rubiaceae) and its four main clades 1 = Carpacoce 2 = Anthosperminae 3 = Operculariinae4 = Coprosminae (Rydin et al 2009) The phylogeny is 1 (2 (3 + 4)) Black dots = localities of Coprosminae on Pacific islands east of AustraliaOpen circle with ldquoxrdquo = fossil pollen on Easter Island


vicariance of a pan-austral ancestor (Heads in press)Subsequent dispersal of the subtribes has been restrictedto South Africa and part of SE Australia explaining thelocal overlap there The basal node involves a breaksomewhere in or around South Africa and this is fol-lowed by breaks in the Indian and Atlantic Oceans Thesame sequence is seen in the breakup of Gondwana Thebreak in SE Australia between Operculariinae andCoprosminae coincides with the pre-drift rifting anduplift that took place in this part of Gondwana in themid-Cretaceous at ~100 MaThe Pacific contingent of Anthospermeae the sub-

tribe Coprosminae has originated persisted andevolved in its own particular sector by means ofmetapopulation survival and evolution and there is noneed for it to have invaded the region There is noessential difference between the evolution of this lar-gely oceanic group and that of its continental relativesin Africa and Australia

Metapopulation vicariance in the south-west Pacific

The idea that the degree of an islandrsquos isolation iskey to understanding its biota can be abandonedinstead the main factor determining the biota of a sitemdashwhether insular or continentalmdashis the sitersquos locationThe biotas of Vanuatu and Fiji for example havebeen determined by their development around conver-gent and divergent plate margins In another case fromMelanesia the flora of New Caledonia has a ldquogoodclaim to be considered the most remarkable in theworldrdquo (Thorne 1965 p 1) For example it includes43 endemic conifers (one parasitic) and several ende-mic angiosperm families This is not explained by theislandrsquos distance from the nearest mainland or its size(18 600 km2 about that of Wales or Massachusetts)but by its particular location in the SW Pacific one ofthe most complex tectonic regions on EarthMany studies of groups in the SW Pacific have

described spatial coincidence between well-documentedbiogeographical patterns and major tectonic features(reviewed in Heads 2014 2016) One important pro-cess in the construction of New Caledonia New Gui-nea and New Zealand has been the repeated accretionof island arcs and intraplate seamounts to the main-lands and this would have provided a rich source ofterrestrial and marine groups Fracturing of theaccreted arcs into segments both before and afteraccretion will have led to metapopulation vicarianceand endemismOne recent study on Australasian birds suggested

that

ldquoVicariance has not been considered to be a significant pro-

cess of speciation in archipelagoes because many islands were

never connected to other landmasses in the past (ie isolated

volcanic islands) However at least two factors make vicari-

ance a plausible and potentially common mode of speciation

in island settingsrdquo (Weeks and Claramunt 2014 p 4)

The first factor that these authors cited was fluctuationin sea level This can cause subdivision and reconnec-tion of islands and the process has been used toexplain many biogeographic patterns But the authorsrsquosecond factor has been neglected They wrote ldquo most islands have not been completely isolatedthroughout their history but are part of tectonicallydynamic archipelagoes with complex geological histo-ries of fragmentation and collisionrdquo (p 4 italicsadded)Weeks and Claramunt (2014) also stressed the great

evolutionary power of vicariance They observed thatldquowhereas a single long-distance dispersal event usuallyinvolves an individual lineage a single vicariance eventcan affect entire biotas potentially leading to multiplespeciation events As a consequence even if not com-mon vicariance can be responsible for a substantialportion of speciation events in archipelagosrdquo (p 4)Weeks and Claramunt (2014) were writing on birds

in the SW Pacific but vicariance mediated by tectonicshas also been used to explain evolution there in inver-tebrates such as oribatid mites These have been inter-preted as ldquoolder taxa persisting on younger islandthrough localised dispersal within island arc metapop-ulations [The distribution pattern] is consistent withthe hypothesis of differentiation of old metapopula-tions by vicariance as plates drifted apart older vol-canic islands subsided and new ones emerged rdquo(Colloff and Cameron 2014 p 272)

Conclusions

The long-term persistence of volcanic activity at par-ticular centres means that terrestrial groups in oceanicsettings could have survived there as metapopulationsmore or less in situ for tens of millions of years Italso means that they could have evolved in situ andoriginated by vicariance with their relatives Metapop-ulation vicariance in archipelagos of young islands islikely to occur with migration of an arc away from acontinent with the rifting of arcs at transform faultswith divergence at spreading ridges with sea floor sub-sidence caused by sea floor cooling and volcanic load-ing and with global change in sea level With themassive subsidence of the Pacific plate for examplemany metapopulations that were widespread andmobile in the Mesozoic would have settled downthrough the Cenozoic into isolated clusters of immo-bile more or less local endemics displaying differentlevels of differentiationIn practice many areas will have experienced more

than one of the mechanisms that cause metapopulation


vicariance For example most intraplate archipelagos inthe central Pacific will have been affected by rifting atmid-ocean ridges sea floor subsidence volcanic loadingand Pleistocene sea level changeAs a result of metapopulation dynamics many

archipelagos host endemic species that are much olderthan any of the individual islands Likewise on conti-nents many regionally endemic species occur in habi-tat islands such as mountains new landslides oldtermite mounds leaves and puddles that are all indi-vidually ephemeral Yet these habitat islands are occu-pied by species that are much older than any individualmountain landslide termite mound puddle or leafThe existence of metapopulations means there is no

fundamental difference between the biogeographicalevolution of land organisms on continents and thosein oceanic habitats Likewise similar processes thatgovern terrestrial metapopulations on oceanic islandsalso determine the dynamics of reef organisms thereas the latter depend on barely submerged substratemdashapatchy habitat in the oceans A study of the wide-spread barnacle genus Chthamalus concludedldquoAlthough individual islands are ephemeral regio-nal endemics [can] survive and evolve as metapopula-tions [I]sland biogeographers should turn fromstudying the age and extrapolated ages of individualislands to re-examining the general history and evolu-tion of subduction zones spreading centers fissuresarcs back-arc basins and accreted terranesrdquo (OrsquoRior-dan et al 2010 p 50)

Acknowledgements

I am grateful to Patricio Saldivia Malte Ebach andan anonymous reviewer for their helpful commentsand suggestions

References

Anderson DL 2010 Hawaii boundary layers and ambient mantlemdashgeophysical constraints J Petrol 52 1547ndash1577

Ashwal LD Wiedenbeck M Torsvik TH 2017 Archaeanzircons in Miocene oceanic hotspot rocks establish ancientcontinental crust beneath Mauritius Nat Commun 8 1ndash9

Baldwin BG Wood KR 2016 Origin of the Rapa endemicgenus Apostates revisiting major disjunctions and evolutionaryconservatism in the Bahia alliance (Compositae Bahieae) Taxon65 1064ndash1080

Beverley SM Wilson AC 1985 Ancient origin for HawaiianDrosophilinae inferred from protein comparisons Proc NatlAcad Sci USA 82 4753ndash4757

Bonneville A 2009 French Polynesia geology In Gillespie RGClague DA (Eds) Encyclopedia of Islands University ofCalifornia Press Berkeley CA pp 338ndash343

Borregaard MK Amorim IR Borges PAV Cabral JSFernandez-Palacios JM Field R Heaney LR Kreft HMatthews TJ Olesen JM Price J Rigal F SteinbauerMJ Triantis KA Valente L Weigelt P Whittaker RJ

2017 Oceanic island biogeography through the lens of thegeneral dynamic model assessment and prospect Biol Rev 92830ndash853

Cantley JT Markey AS Swenson NG Keeley SC 2016Biogeography and evolutionary diversification in one of the mostwidely distributed and species rich genera of the Pacific AoBPlants 8 plw043

Carr LM McLenachan PA Waddell PJ Gemmell NJPenny D 2015 Analyses of the mitochondrial genome ofLeiopelma hochstetteri argues against the full drowning of NewZealand J Biogeogr 42 1066ndash1076

Clague DA 1996 The growth and subsidence of the Hawaiian-Emperor volcanic chain In Keast A Miller S (Eds) TheOrigin and Evolution of Pacific Island Biotas New Guinea toEastern Polynesia SPB Academic Publishing Amsterdam pp35ndash50

Colley H Hindle WH 1984 Volcano-tectonic evolution of Fijiand adjoining marginal basins Geol Soc London Special Publ16 151ndash162

Colloff MJ Cameron SL 2014 Beyond Moarsquos Ark andWallacersquos Line extralimital distribution of new species ofAustronothrus (Acari Oribatida Crotoniidae) and the endemicityof the New Zealand oribatid mite fauna Zootaxa 3780 263ndash281

Cronin SJ Ferland MA Terry TP 2003 Nabukelevu volcano(Mt Washington) Kadavu ndash a source of hitherto unknownvolcanic hazard in Fiji J Volcanol Geothermal Res 131 371ndash396

Darwin C 1859 On the Origin of Species 1st edn John MurrayLondon

De Baets K Antonelli A Donoghue PC 2016 Tectonic blocksand molecular clocks Philos Trans R Soc Lond B Biol Sci371 20160098

Ebach MC Williams DM 2016 Dispersalism andneodispersalism In Williams D Schmitt M Wheeler Q(Eds) The Future of Phylogenetic Systematics The Legacy ofWilli Hennig Cambridge University Press Cambridge UK pp286ndash329

Foulger GR Panza GF Artemieva IM Bastow IDCammarano F Evans JR Hamilton WB Julian BRLustrino M Thybo H Yanovskaya TB 2013 Caveats ontomographic images Terra Nova 25 259ndash281

Franzke A Koch MA Mummenhoff K 2016 Turnip timetravels age estimates in Brassicaceae Trends Plant Sci 21 554ndash561

Gillespie RG Roderick GK 2002 Arthropods on islandscolonization speciation and conservation Annu Rev Entomol47 595ndash632

Gilpin ME Hanski IA (Eds) 1997 Metapopulation BiologyEcology Genetics and Evolution Academic Press San DiegoCA

Hamilton WB 2011 Plate tectonics began in Neoproterozoic timeand plumes from deep mantle have never operated Lithos 1231ndash20

Hanski IA 1999 Metapopulation Ecology Oxford UniversityPress Oxford UK

Hanski IA 2010 Island biogeography and metapopulations InLosos JB Ricklefs RE (Eds) The Theory of IslandBiogeography Revisited Princeton University Press PrincetonNJ pp 186ndash213

Hanski IA Gaggiotti OE (Eds) 2004 Ecology Genetics andEvolution of Metapopulations Elsevier Burlington MA

Heads M 2006 Seed plants of Fiji an ecological analysis Biol JLinn Soc 89 407ndash431

Heads M 2008 Panbiogeography of New Caledonia southwestPacific basal angiosperms on basement terranes ultramaficendemics inherited from volcanic arcs and old taxa endemic toyoung islands J Biogeogr 35 2153ndash2175

Heads M 2011 Old taxa on young islands a critique of the use ofisland age to date island-endemic clades and calibratephylogenies Syst Biol 60 204ndash218

Heads M 2012 Molecular Panbiogeography of the TropicsUniversity of California Press Berkeley CA


Heads M 2014 Biogeography of Australasia A MolecularAnalysis Cambridge University Press Cambridge UK

Heads M 2016 Biogeography and Evolution in New ZealandTaylor amp FrancisCRC Boca Raton FL

Heads M in press Metapopulation vicariance in the Pacific genusCoprosma (Rubiaceae) and its Gondwanan relatives Aust SystBot

Hillier JK Watts AB 2005 Relationship between depth and agein the North Pacific Ocean J Geophys Res 110 B02405httpsdoiorg1010292004jb003406

Holland B 2012 If the conceptual straitjacket fits chances areyoursquore already wearing it Front Biogeogr 4 144ndash147

IUCN 2016 The IUCN redlist of threatened species wwwiucnredlistorg

Johnson SB Young CR Jones WJ Waren A VrijenhoekRC 2006 Migration isolation and speciation of hydrothermalvent limpets (Gastropoda Lepetodrilidae) across the BlancoTransform Fault Biol Bull 210 140ndash157

Kumar S Hedges SB 2016 Advances in time estimationmethods for molecular data Mol Biol Evol 33 863ndash869

Landis MJ 2017 Biogeographic dating of speciation timesusing paleogeographically informed processes Syst Biol 66128ndash144

Le Pechon T Dai Q Zhang LB Gao XF Sauquet H 2015Diversification of Dombeyoideae (Malvaceae) in the Mascarenesold taxa on young islands Int J Plant Sci 176 211ndash221

Lomolino MV Riddle BR Whittaker RJ Brown JH 2010Biogeography 4th edn Sinauer Sunderland MA

Lovette IJ Arbogast BS Curry RI Zink RM Botero CASullivan JP Talaba AL Harris RB Rubenstein DRRicklefs RE Bermingham E 2012 Phylogenetic relationshipsof the mockingbirds and thrashers (Aves Mimidae) MolPhylogenet Evol 63 219ndash229

MacArthur RH Wilson EO 1967 The Theory of IslandBiogeography Princeton University Press Princeton NJ

Martin AK 2013 Double-saloon-door tectonics in the North FijiBasin Earth Planet Sci Lett 374 191ndash203

Matzke NJ 2015 Review of ldquoBiogeography of Australasia AMolecular Analysisrdquo by Michael Heads Q Rev Biol 90 327ndash328

Moalic Y Desbruyeres D Duarte CM Rozenfeld AFBachraty C Arnaud-Haond S 2011 Biogeography revisitedwith network theory retracing the history of hydrothermal ventcommunities Syst Biol 61 127ndash137

Monaghan MT Balke M Pons J Vogler AP 2006 Beyondbarcodes complex DNA taxonomy of a South Pacific Islandradiation Proc R Soc B Lond Biol Sci 273 887ndash893

Mort ME Randle CP Kimball RT Tadesse M CrawfordDJ 2008 Phylogeny of Coreopsideae (Asteraceae) inferredfrom nuclear and plastid DNA sequences Taxon 57 109ndash120

Nunn PD Baniala M Harrison M Geraghty P 2006Vanished islands in Vanuatu new research and a preliminarygeohazard assessment J R Soc N Z 36 37ndash50

OrsquoGrady PM Bennett GM Funk VA Altheide TK 2012Retrograde biogeography Taxon 61 699ndash705

OrsquoRiordan RM Power AM Myers AA 2010 Factors atdifferent scales affecting the distribution of species of the genusChthamalus Ranzani (Cirripedia Balanomorpha Chthamaloidea)J Exp Mar Biol Ecol 392 46ndash64

Patriat M Collot J Danyushevsky L Fabre M Meffre SFalloon T Rouillard P Pelletier B Roach M Fournier M2015 Propagation of back-arc extension into the arc lithospherein the southern New Hebrides volcanic arc Geochem GeophysGeosyst 16 3142ndash3159

Pindell JL Kennan L 2009 Tectonic evolution of the Gulf ofMexico Caribbean and northern South America in the mantlereference frame an update Geol Soc London Special Publ 3281ndash55

Plouviez S Shank TM Faure B Daguin-Thiebaut C ViardF Lallier FH Jollivet D 2009 Comparative phylogeographyamong hydrothermal vent species along the East Pacific Rise

reveals vicariant processes and population expansion in thesouth Mol Ecol 18 3903ndash3917

van der Pluijm BA Marshak M 2004 Earth Structure An Intro-duction to Structural Geology and Tectonics 2nd edn NortonNew York

Price JP Clague DA 2002 How old is the Hawaiian biotaGeology and phylogeny suggest recent divergence Proc R SocB Lond Biol Sci 269 2429ndash2435

dos Reis M Donoghue PC Yang Z 2016 Bayesian molecularclock dating of species divergences in the genomics era NatRev Genet 17 71ndash80

Rose J Koppers AAP 2014 An evaluation of the complex ageprogression along the Cook-Austral Islands using high-resolution40Ar39Ar incremental heating ages In American GeophysicalUnion Fall Meeting 2014 (San Francisco) Abstract DI43A-4360httpsuiadsabsharvardeduabs2014AGUFMDI43A4360Rabstract

Rydin C Razafimandimbison SG Khodabandeh A Bremer B2009 Evolutionary relationships in the Spermacoceae alliance(Rubiaceae) using information from six molecular loci insightsinto systematic affinities of Neohymenopogon and MouretiaTaxon 58 793ndash810

Sano T Shimizu K Ishikawa A Senda R Chang Q Kimura JIWiddowson M Sager WW 2012 Variety and origin of magmason Shatsky Rise northwest Pacific Ocean Geochem GeophysGeosyst 13(8) 1ndash25 httpsdoiorg1010292012gc004235

Schellart WP Lister GS Toy VG 2006 A Late Cretaceousand Cenozoic reconstruction of the Southwest Pacific regiontectonics controlled by subduction and slab rollback processesEarth-Sci Rev 76 191ndash233

Schmalfuss H 2003 World catalog of terrestrial isopods (IsopodaOniscidea) Stuttgarter Beitr Naturk Ser A 654 1ndash341

Smith AC 1979ndash1996 Flora Vitiensis Nova A New Flora of Fiji(Spermatophytes only) 6 vols Pacific Tropical BotanicalGarden Kauai Hawaii

Smith AD 2007 A plate model for Jurassic to Recent intraplatevolcanism in the Pacific Ocean basin Geol Soc Am Spec Pap430 471ndash495

Spalik K Banasiak Ł Feist MAE Downie SR 2014Recurrent short-distance dispersal explains wide distributions ofhydrophytic umbellifers (Apiaceae tribe Oenantheae) JBiogeogr 41 1559ndash1571

Sykes WR 1998 Scaevola gracilis (Goodeniaceae) in theKermadec Islands and Tonga N Z J Bot 36 671ndash674

Telegraph [London] 2015 First photographs emerge of new Pacificisland off Tonga wwwtelegraphcouknewsworldnewsaustraliaandthepacifictongafrenchpolynesia11463853First-photographs-emerge-of-new-Pacific-island-off-Tongahtml

Thorne RF 1965 Floristic relationships of New Caledonia UnivIowa Studies Nat Hist 20(7) 1ndash14

Triantis KA Whittaker RJ Fernandez-Palacios JM GeistDJ 2016 Oceanic archipelagos a perspective on thegeodynamics and biogeography of the worldrsquos smallest bioticprovinces Front Biogeogr 82 e29605 pp 1-9

Vrijenhoek RC 2010 Genetic diversity and connectivity of deep-seahydrothermal vent metapopulations Mol Ecol 19 4391ndash4411

Weeks BC Claramunt S 2014 Dispersal has inhibited aviandiversification in Australasian archipelagoes Proc R Soc B 28120141257

Whittaker RJ Fernandez-Palacios JM 2007 IslandBiogeography Ecology Evolution and Conservation 2nd ednOxford University Press Oxford UK

Whittaker RJ Triantis KA Ladle RJ 2008 A generaldynamic theory of oceanic island biogeography J Biogeogr 35977ndash994

Whittaker RJ Triantis KA Ladle RJ 2010 A generaldynamic theory of oceanic island biogeography extending theMacArthurndashWilson theory to accommodate the rise and fall ofvolcanic islands In Losos JB Ricklefs RE (Eds) TheTheory of Island Biogeography Revisited Princeton UniversityPress Princeton NJ pp 88ndash115


Wikstreuroom N Kainulainen K Razafimandimbison SGSmedmark JEE Bremer B 2015 A revised time tree of theasterids establishing a temporal framework for evolutionarystudies of the coffee family (Rubiaceae) PLoS ONE 10e0126690 pp 1-26

Zhong S Ritzwoller M Shapiro N Landuyt W Huang JWessel P 2007 Bathymetry of the Pacific plate and itsimplications for thermal evolution of lithosphere and mantledynamics J Geophys Res 112 B06412 httpsdoiorg1010292006jb004628


as a metapopulation that is a population of distinctsub-populations that are separated geographically butconnected by dispersalIndividual habitat islands and their populations are

often ephemeral Yet the constant production of newhabitat islands can lead to long-term survival of thespecies depending on the balance between local extinc-tions and recolonizations in the patchwork of frag-mented landscape (Hanski 1999) The process permitsldquothe metapopulation persistence of unstable but moreor less independently fluctuating local populationsrdquo(Hanski 1999 p 11)This model provides a good description of the popu-

lation dynamics in many species that inhabit activevolcanic archipelagos Metapopulations persist therethrough constant colonization of younger activeislands from older extinct ones and the latter eventu-ally subside Volcanic islands are short-lived in geolog-ical time but the volcanic centres that generate themare much older Most archipelagos in the central Paci-fic for example have been active for tens of millionsof years although their current islands are all muchyounger than thisThe metapopulation model explains how a group

can survive in a dynamic region In addition activevolcanic centres are often rifted apart into separateactive sections (eg at subduction zones offset bytransform faults) and so it is likely that the popula-tions there can also differentiate If an active volcanicarchipelago hosting a metapopulation is divided intoseparate active segments moving away from eachother the genetic cohesion of the metapopulation willbe reduced and eventually fail and vicariance into twoor more metapopulations can result Thus tectonicchanges including those discussed below can breakup widespread insular metapopulations and produceendemics restricted to fewer islands or even a singleisland Many regional zones of oceanic volcanism havebeen rifted apart and so clades endemic to young vol-canic islands there are likely to originate by vicarianceof widespread ancestors For example a group inhab-iting young volcanic islands in western Polynesia andits sister group with similar ecology in eastern Polyne-sia could both be derived from a widespread Pacificgroup that has been ruptured by sea floor spreading atthe East Pacific Rise Molecular phylogenetic studiesare documenting a growing number of such patternswith precise allopatry among terrestrial insular cladesthat each occupy a large sector of the Pacific (Heads2012 2014) and these could be the result of simplevicariance in an oceanic settingThis ldquometapopulation vicariancerdquo model of island

biogeography differs from the standard one in the sig-nificance attached to former islands In traditional the-ory these act as ldquohalting-placesrdquo or ldquostepping stonesrdquothat facilitate migration of rare individuals from a

continent to a distant island In contrast the metapop-ulation model proposes that the sequential emergenceof past present and future islands allows a metapopu-lation to survive in its particular region more or lessin situ and so it is not necessary to assume that thegroups have dispersed there from a continent In the-ory a lineage can persist in an insular region more orless indefinitely for as long as new islands are beingproduced

Earlier theories of island biogeography

The ldquoequilibrium theory of island biogeographyrdquo

Island biogeography has been explained in severalways The best known is MacArthur and Wilsonrsquos(1967) ldquoequilibrium theory of island biogeographyrdquoThis proposed that the two main processes determin-ing an islandrsquos biota were dispersal from the nearestmainland and extinction of groups on the island Vari-ation in these processes was in turn attributed to theislandrsquos area and its distance from the mainland Thetheory did not consider the islandrsquos specific location onthe Earthrsquos surface or the tectonic history of the vol-canic centre that produced the islandMacArthur and Wilsonrsquos (1967) model is still widely

accepted For example one illustrated scenario for anew volcanic island began with a large blank spacelabelled ldquoNothingrdquo (Gillespie and Roderick 2002fig 1) In this scenario the site has no geographicallocation and in particular no tectonic contextAlthough MacArthur and Wilson (1967) assumed

that mainland-to-island dispersal is a key factor deter-mining island biota ldquomigration among the islands isignoredrdquo (Hanski 2010 p 189) Yet migration amongneighbouring islands is a common process and it isprobably critical for evolution This is not because itleads to speciation but because it allows thepersistence of metapopulations more or less in situ forexample in the region occupied by a singlearchipelago

The ldquogeneral dynamic model (GDM) of oceanic islandbiogeographyrdquo

A recent model of oceanic island biogeography rep-resents an advance over the ecological approach ofMacArthur and Wilson (1967) as it incorporates thegeological ldquolife cyclerdquo of a volcanic island from smallto large and then small again (Whittaker et al 20082010) ldquoThe general dynamic model of oceanic islandbiogeography (GDM) has added a new dimension totheoretical island biogeography in recognizing thatgeological processes are key drivers of the evolutionaryprocesses of diversification and extinction within
























































Time 1

Time 2

Trench

Arc
















































Trench rollback

Time 1 Time 2





WestAntarctica

Australia

HikurangiPlateau

Antarctica

Australia

HikurangiPlateau

Australia

HikurangiPlateau

Australia

90 Ma

75 Ma

50 Ma

60 Ma

Australia

45 Ma

Australia

35 Ma

12

12

2

BT

T

CSBCSB

SLSL

NC

2

LT

VTKNL

2 1

NRLHR

VTKLT

East Ant- arctica

East Ant- arctica

SLSL






Australia

15 Ma

Australia

10 Ma

Australia

5 Ma

Australia

Present

12

33

2

1

1

2 3

2

3

1

23

NFLL

LCTKTK

LC

Fig 3 Continued














Time 2

Fracture zone

Fracture zone

Transform margin

Time 1



Island arc


1

2

4 5 3

Caribbean plate








Vanuatu

NewCaledonia

New Caledonia

LauRidgeLau Ridge


Loyalty Ridge

TongaTonga

SamoaMBP

SLBSLB

LB

NR

TavTav

LauLau

OJP

Vitiaz trench

Hunter fractu

rezo

ne

LHR

= 1 = 2 = 3 = 4 = 5 = 6

LoyLoy

Fiji fracture zone

SCSC

500 km

FijiFiji

180deg170deg

15deg

20deg


Present

120 Ma120 Ma

1001008484

7171 5656 4646 33331919

1010



















Dating clades

























2016 p 554)


















1

2

3


x








that










Conclusions







Acknowledgements


References





































































































































Time 1

Time 2

Trench

Arc
















































Trench rollback

Time 1 Time 2





WestAntarctica

Australia

HikurangiPlateau

Antarctica

Australia

HikurangiPlateau

Australia

HikurangiPlateau

Australia

90 Ma

75 Ma

50 Ma

60 Ma

Australia

45 Ma

Australia

35 Ma

12

12

2

BT

T

CSBCSB

SLSL

NC

2

LT

VTKNL

2 1

NRLHR

VTKLT

East Ant- arctica

East Ant- arctica

SLSL






Australia

15 Ma

Australia

10 Ma

Australia

5 Ma

Australia

Present

12

33

2

1

1

2 3

2

3

1

23

NFLL

LCTKTK

LC

Fig 3 Continued














Time 2

Fracture zone

Fracture zone

Transform margin

Time 1



Island arc


1

2

4 5 3

Caribbean plate








Vanuatu

NewCaledonia

New Caledonia

LauRidgeLau Ridge


Loyalty Ridge

TongaTonga

SamoaMBP

SLBSLB

LB

NR

TavTav

LauLau

OJP

Vitiaz trench

Hunter fractu

rezo

ne

LHR

= 1 = 2 = 3 = 4 = 5 = 6

LoyLoy

Fiji fracture zone

SCSC

500 km

FijiFiji

180deg170deg

15deg

20deg


Present

120 Ma120 Ma

1001008484

7171 5656 4646 33331919

1010



















Dating clades

























2016 p 554)


















1

2

3


x








that










Conclusions







Acknowledgements


References

























































































































Time 1

Time 2

Trench

Arc
















































Trench rollback

Time 1 Time 2





WestAntarctica

Australia

HikurangiPlateau

Antarctica

Australia

HikurangiPlateau

Australia

HikurangiPlateau

Australia

90 Ma

75 Ma

50 Ma

60 Ma

Australia

45 Ma

Australia

35 Ma

12

12

2

BT

T

CSBCSB

SLSL

NC

2

LT

VTKNL

2 1

NRLHR

VTKLT

East Ant- arctica

East Ant- arctica

SLSL






Australia

15 Ma

Australia

10 Ma

Australia

5 Ma

Australia

Present

12

33

2

1

1

2 3

2

3

1

23

NFLL

LCTKTK

LC

Fig 3 Continued














Time 2

Fracture zone

Fracture zone

Transform margin

Time 1



Island arc


1

2

4 5 3

Caribbean plate








Vanuatu

NewCaledonia

New Caledonia

LauRidgeLau Ridge


Loyalty Ridge

TongaTonga

SamoaMBP

SLBSLB

LB

NR

TavTav

LauLau

OJP

Vitiaz trench

Hunter fractu

rezo

ne

LHR

= 1 = 2 = 3 = 4 = 5 = 6

LoyLoy

Fiji fracture zone

SCSC

500 km

FijiFiji

180deg170deg

15deg

20deg


Present

120 Ma120 Ma

1001008484

7171 5656 4646 33331919

1010



















Dating clades

























2016 p 554)


















1

2

3


x








that










Conclusions







Acknowledgements


References









































































































Time 1

Time 2

Trench

Arc
















































Trench rollback

Time 1 Time 2





WestAntarctica

Australia

HikurangiPlateau

Antarctica

Australia

HikurangiPlateau

Australia

HikurangiPlateau

Australia

90 Ma

75 Ma

50 Ma

60 Ma

Australia

45 Ma

Australia

35 Ma

12

12

2

BT

T

CSBCSB

SLSL

NC

2

LT

VTKNL

2 1

NRLHR

VTKLT

East Ant- arctica

East Ant- arctica

SLSL






Australia

15 Ma

Australia

10 Ma

Australia

5 Ma

Australia

Present

12

33

2

1

1

2 3

2

3

1

23

NFLL

LCTKTK

LC

Fig 3 Continued














Time 2

Fracture zone

Fracture zone

Transform margin

Time 1



Island arc


1

2

4 5 3

Caribbean plate








Vanuatu

NewCaledonia

New Caledonia

LauRidgeLau Ridge


Loyalty Ridge

TongaTonga

SamoaMBP

SLBSLB

LB

NR

TavTav

LauLau

OJP

Vitiaz trench

Hunter fractu

rezo

ne

LHR

= 1 = 2 = 3 = 4 = 5 = 6

LoyLoy

Fiji fracture zone

SCSC

500 km

FijiFiji

180deg170deg

15deg

20deg


Present

120 Ma120 Ma

1001008484

7171 5656 4646 33331919

1010



















Dating clades

























2016 p 554)


















1

2

3


x








that










Conclusions







Acknowledgements


References



























































































Time 1

Time 2

Trench

Arc
















































Trench rollback

Time 1 Time 2





WestAntarctica

Australia

HikurangiPlateau

Antarctica

Australia

HikurangiPlateau

Australia

HikurangiPlateau

Australia

90 Ma

75 Ma

50 Ma

60 Ma

Australia

45 Ma

Australia

35 Ma

12

12

2

BT

T

CSBCSB

SLSL

NC

2

LT

VTKNL

2 1

NRLHR

VTKLT

East Ant- arctica

East Ant- arctica

SLSL






Australia

15 Ma

Australia

10 Ma

Australia

5 Ma

Australia

Present

12

33

2

1

1

2 3

2

3

1

23

NFLL

LCTKTK

LC

Fig 3 Continued














Time 2

Fracture zone

Fracture zone

Transform margin

Time 1



Island arc


1

2

4 5 3

Caribbean plate








Vanuatu

NewCaledonia

New Caledonia

LauRidgeLau Ridge


Loyalty Ridge

TongaTonga

SamoaMBP

SLBSLB

LB

NR

TavTav

LauLau

OJP

Vitiaz trench

Hunter fractu

rezo

ne

LHR

= 1 = 2 = 3 = 4 = 5 = 6

LoyLoy

Fiji fracture zone

SCSC

500 km

FijiFiji

180deg170deg

15deg

20deg


Present

120 Ma120 Ma

1001008484

7171 5656 4646 33331919

1010



















Dating clades

























2016 p 554)


















1

2

3


x








that










Conclusions







Acknowledgements


References




























































































































Trench rollback

Time 1 Time 2





WestAntarctica

Australia

HikurangiPlateau

Antarctica

Australia

HikurangiPlateau

Australia

HikurangiPlateau

Australia

90 Ma

75 Ma

50 Ma

60 Ma

Australia

45 Ma

Australia

35 Ma

12

12

2

BT

T

CSBCSB

SLSL

NC

2

LT

VTKNL

2 1

NRLHR

VTKLT

East Ant- arctica

East Ant- arctica

SLSL






Australia

15 Ma

Australia

10 Ma

Australia

5 Ma

Australia

Present

12

33

2

1

1

2 3

2

3

1

23

NFLL

LCTKTK

LC

Fig 3 Continued














Time 2

Fracture zone

Fracture zone

Transform margin

Time 1



Island arc


1

2

4 5 3

Caribbean plate








Vanuatu

NewCaledonia

New Caledonia

LauRidgeLau Ridge


Loyalty Ridge

TongaTonga

SamoaMBP

SLBSLB

LB

NR

TavTav

LauLau

OJP

Vitiaz trench

Hunter fractu

rezo

ne

LHR

= 1 = 2 = 3 = 4 = 5 = 6

LoyLoy

Fiji fracture zone

SCSC

500 km

FijiFiji

180deg170deg

15deg

20deg


Present

120 Ma120 Ma

1001008484

7171 5656 4646 33331919

1010



















Dating clades

























2016 p 554)


















1

2

3


x








that










Conclusions







Acknowledgements


References













































































































Trench rollback

Time 1 Time 2





WestAntarctica

Australia

HikurangiPlateau

Antarctica

Australia

HikurangiPlateau

Australia

HikurangiPlateau

Australia

90 Ma

75 Ma

50 Ma

60 Ma

Australia

45 Ma

Australia

35 Ma

12

12

2

BT

T

CSBCSB

SLSL

NC

2

LT

VTKNL

2 1

NRLHR

VTKLT

East Ant- arctica

East Ant- arctica

SLSL






Australia

15 Ma

Australia

10 Ma

Australia

5 Ma

Australia

Present

12

33

2

1

1

2 3

2

3

1

23

NFLL

LCTKTK

LC

Fig 3 Continued














Time 2

Fracture zone

Fracture zone

Transform margin

Time 1



Island arc


1

2

4 5 3

Caribbean plate








Vanuatu

NewCaledonia

New Caledonia

LauRidgeLau Ridge


Loyalty Ridge

TongaTonga

SamoaMBP

SLBSLB

LB

NR

TavTav

LauLau

OJP

Vitiaz trench

Hunter fractu

rezo

ne

LHR

= 1 = 2 = 3 = 4 = 5 = 6

LoyLoy

Fiji fracture zone

SCSC

500 km

FijiFiji

180deg170deg

15deg

20deg


Present

120 Ma120 Ma

1001008484

7171 5656 4646 33331919

1010



















Dating clades

























2016 p 554)


















1

2

3


x








that










Conclusions







Acknowledgements


References



























































































Trench rollback

Time 1 Time 2





WestAntarctica

Australia

HikurangiPlateau

Antarctica

Australia

HikurangiPlateau

Australia

HikurangiPlateau

Australia

90 Ma

75 Ma

50 Ma

60 Ma

Australia

45 Ma

Australia

35 Ma

12

12

2

BT

T

CSBCSB

SLSL

NC

2

LT

VTKNL

2 1

NRLHR

VTKLT

East Ant- arctica

East Ant- arctica

SLSL






Australia

15 Ma

Australia

10 Ma

Australia

5 Ma

Australia

Present

12

33

2

1

1

2 3

2

3

1

23

NFLL

LCTKTK

LC

Fig 3 Continued














Time 2

Fracture zone

Fracture zone

Transform margin

Time 1



Island arc


1

2

4 5 3

Caribbean plate








Vanuatu

NewCaledonia

New Caledonia

LauRidgeLau Ridge


Loyalty Ridge

TongaTonga

SamoaMBP

SLBSLB

LB

NR

TavTav

LauLau

OJP

Vitiaz trench

Hunter fractu

rezo

ne

LHR

= 1 = 2 = 3 = 4 = 5 = 6

LoyLoy

Fiji fracture zone

SCSC

500 km

FijiFiji

180deg170deg

15deg

20deg


Present

120 Ma120 Ma

1001008484

7171 5656 4646 33331919

1010



















Dating clades

























2016 p 554)


















1

2

3


x








that










Conclusions







Acknowledgements


References















































































WestAntarctica

Australia

HikurangiPlateau

Antarctica

Australia

HikurangiPlateau

Australia

HikurangiPlateau

Australia

90 Ma

75 Ma

50 Ma

60 Ma

Australia

45 Ma

Australia

35 Ma

12

12

2

BT

T

CSBCSB

SLSL

NC

2

LT

VTKNL

2 1

NRLHR

VTKLT

East Ant- arctica

East Ant- arctica

SLSL






Australia

15 Ma

Australia

10 Ma

Australia

5 Ma

Australia

Present

12

33

2

1

1

2 3

2

3

1

23

NFLL

LCTKTK

LC

Fig 3 Continued














Time 2

Fracture zone

Fracture zone

Transform margin

Time 1



Island arc


1

2

4 5 3

Caribbean plate








Vanuatu

NewCaledonia

New Caledonia

LauRidgeLau Ridge


Loyalty Ridge

TongaTonga

SamoaMBP

SLBSLB

LB

NR

TavTav

LauLau

OJP

Vitiaz trench

Hunter fractu

rezo

ne

LHR

= 1 = 2 = 3 = 4 = 5 = 6

LoyLoy

Fiji fracture zone

SCSC

500 km

FijiFiji

180deg170deg

15deg

20deg


Present

120 Ma120 Ma

1001008484

7171 5656 4646 33331919

1010



















Dating clades

























2016 p 554)


















1

2

3


x








that










Conclusions







Acknowledgements


References



















































































Australia

15 Ma

Australia

10 Ma

Australia

5 Ma

Australia

Present

12

33

2

1

1

2 3

2

3

1

23

NFLL

LCTKTK

LC

Fig 3 Continued














Time 2

Fracture zone

Fracture zone

Transform margin

Time 1



Island arc


1

2

4 5 3

Caribbean plate








Vanuatu

NewCaledonia

New Caledonia

LauRidgeLau Ridge


Loyalty Ridge

TongaTonga

SamoaMBP

SLBSLB

LB

NR

TavTav

LauLau

OJP

Vitiaz trench

Hunter fractu

rezo

ne

LHR

= 1 = 2 = 3 = 4 = 5 = 6

LoyLoy

Fiji fracture zone

SCSC

500 km

FijiFiji

180deg170deg

15deg

20deg


Present

120 Ma120 Ma

1001008484

7171 5656 4646 33331919

1010



















Dating clades

























2016 p 554)


















1

2

3


x








that










Conclusions







Acknowledgements


References


























































































Time 2

Fracture zone

Fracture zone

Transform margin

Time 1



Island arc


1

2

4 5 3

Caribbean plate








Vanuatu

NewCaledonia

New Caledonia

LauRidgeLau Ridge


Loyalty Ridge

TongaTonga

SamoaMBP

SLBSLB

LB

NR

TavTav

LauLau

OJP

Vitiaz trench

Hunter fractu

rezo

ne

LHR

= 1 = 2 = 3 = 4 = 5 = 6

LoyLoy

Fiji fracture zone

SCSC

500 km

FijiFiji

180deg170deg

15deg

20deg


Present

120 Ma120 Ma

1001008484

7171 5656 4646 33331919

1010



















Dating clades

























2016 p 554)


















1

2

3


x








that










Conclusions







Acknowledgements


References



















































































Vanuatu

NewCaledonia

New Caledonia

LauRidgeLau Ridge


Loyalty Ridge

TongaTonga

SamoaMBP

SLBSLB

LB

NR

TavTav

LauLau

OJP

Vitiaz trench

Hunter fractu

rezo

ne

LHR

= 1 = 2 = 3 = 4 = 5 = 6

LoyLoy

Fiji fracture zone

SCSC

500 km

FijiFiji

180deg170deg

15deg

20deg


Present

120 Ma120 Ma

1001008484

7171 5656 4646 33331919

1010



















Dating clades

























2016 p 554)


















1

2

3


x








that










Conclusions







Acknowledgements


References































































































Dating clades

























2016 p 554)


















1

2

3


x








that










Conclusions







Acknowledgements


References


















































































Dating clades

























2016 p 554)


















1

2

3


x








that










Conclusions







Acknowledgements


References





















































































2016 p 554)


















1

2

3


x








that










Conclusions







Acknowledgements


References




















































































that










Conclusions







Acknowledgements


References


















































































Acknowledgements


References



































































































































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