Lessons from Red Data Books: Plant Vulnerability Increases with Floral Complexity

18 Pages·2015·1.89 MB·English

RESEARCHARTICLE
Lessons from Red Data Books: Plant
Vulnerability Increases with Floral
Complexity
AnastasiaStefanaki1,2*,AphroditeKantsa1,ThomasTscheulin1,MarthaCharitonidou1,
TheodoraPetanidou1
1 LaboratoryofBiogeographyandEcology,DepartmentofGeography,UniversityoftheAegean,Mytilene,
Greece,2 NaturalisBiodiversityCenter–NationalHerbariumoftheNetherlands,Leiden,Netherlands
*[email protected]
Abstract
Thearchitecturalcomplexityofflowerstructures(hereafterreferredtoasfloralcomplexity)
maybelinkedtopollinationbyspecializedpollinatorsthatcanincreasetheprobabilityof
OPENACCESS successfulseedset.Asplant—pollinatorsystemsbecomefragile,alossofsuchspecial-
izedpollinatorscouldpresumablyresultinanincreasedlikelihoodofpollinationfailure.This
Citation:StefanakiA,KantsaA,TscheulinT,
CharitonidouM,PetanidouT(2015)Lessonsfrom isanissuelikelytobeparticularlyevidentinplantsthatarecurrentlyrare.Usinganovel
RedDataBooks:PlantVulnerabilityIncreaseswith indexdescribingfloralcomplexityweexploredwhetherthisaspectofthestructureofflowers
FloralComplexity.PLoSONE10(9):e0138414.
couldbeusedtopredictvulnerabilityofplantspeciestoextinction.Todothiswedefined
doi:10.1371/journal.pone.0138414
plantvulnerabilityusingtheRedDataBookofRareandThreatenedPlantsofGreece,a
Editor:JeffOllerton,UniversityofNorthampton,
Mediterraneanbiodiversityhotspot.Wealsotestedwhetherotherintrinsic(e.g.lifeform,
UNITEDKINGDOM
asexualreproduction)orextrinsic(e.g.habitat,altitude,range-restrictedness)factorscould
Received:March14,2015
affectplantvulnerability.Wefoundthatplantswithhighfloralcomplexityscoresweresignifi-
Accepted:August30,2015 cantlymorelikelytobevulnerabletoextinction.Amongallthefloralcomplexitycomponents
Published:September21,2015 onlyfloralsymmetrywasfoundtohaveasignificanteffect,withradial-flowerplantsappear-
ingtobelessvulnerable.Lifeformwasalsoapredictorofvulnerability,withwoodyperen-
Copyright:©2015Stefanakietal.Thisisanopen
accessarticledistributedunderthetermsofthe nialplantshavingsignificantlylowerriskofextinction.Amongtheextrinsicfactors,both
CreativeCommonsAttributionLicense,whichpermits habitatandmaximumrangeweresignificantlyassociatedwithplantvulnerability(coastal
unrestricteduse,distribution,andreproductioninany
plantsandnarrow-rangedplantsaremorelikelytofacehigherrisk).Althoughextrinsicand
medium,providedtheoriginalauthorandsourceare
inparticularanthropogenicfactorsdetermineplantextinctionrisk,intrinsictraitscanindicate
credited.
aplant’spronenesstovulnerability.Thisraisesthepotentialthreatofdecliningglobalpolli-
DataAvailabilityStatement:Allrelevantdataare
natordiversityinteractingwithfloralcomplexitytoincreasethevulnerabilityofindividual
withinthepaperanditsSupportinginformationfiles.
plantspecies.Thereispotentialscopeforusingplant—pollinatorspecializationstoidentify
Funding:Thisstudywasco-financedbythe
plantspeciesparticularlyatriskandsotargetconservationeffortstowardsthem.
EuropeanUnion(EuropeanSocialFund[ESF])and
GreeknationalfundsthroughtheOperational
Program"EducationandLifelongLearning"ofthe
NationalStrategicReferenceFramework(NSRF)–
ResearchFundingProgram:THALES–Investingin
knowledgesocietythroughtheEuropeanSocialFund
(seeref.20inthetext).Additionalsupporthasbeen
providedtoASbytheFP7EuropeanprojectSTEP
(seeref.21inthetext).Thefundershadnorolein
PLOSONE|DOI:10.1371/journal.pone.0138414 September21,2015 1/18
PlantVulnerabilityIncreaseswithFloralComplexity
studydesign,datacollectionandanalysis,decisionto Introduction
publish,orpreparationofthemanuscript.
Thecriteriaforthedesignationofendangeredspecies,asestablishedworldwidebytheInterna-
CompetingInterests:Theauthorshavedeclared
tionalUnionfortheConservationofNature(IUCN),arebasedontrendsinpopulationsizes
thatnocompetinginterestsexist.
andgeographicalranges[1].Thesedataareenrichedwithinformationonotherexternal
threats,mostlyanthropogenic,includingoverexploitation,habitatdegradation,pollutants,and
competitionfromintroducedspecies[1].Variouseffortshavebeenmadetocomplementthe
IUCNcriteria(e.g.[2–4]),whichhavefocusedprimarilyongeographicaland/orecologicalfac-
tors,withendemismorhabitatoftencitedasreliablepredictorsofplantvulnerability(e.g.[2]).
Itis,however,possiblethatotherintrinsicfactors,includingthefloweringduration,reproduc-
tionorpollinationmodeofplants,mayaffecttheirvulnerability[5].Incompleteknowledgeof
thereproductionbiologyofmanyrareandthreatenedplants[6,7]impedestheconsideration
ofsuchintrinsictraitsassociatedwiththereproductivesuccessofplants.
Adeterminantofsuccessfulplantreproductionispollination.Acomplexflowerstructure
mayincreaseaplant’schancesofsuccessfulreproductionbyenhancingpollinatorfidelityto
flowersandreducinglarcenybyillegitimatefloralvisitors([8]andreferencestherein).Onthe
otherhand,plantswithcomplexflowersmaybelikelytosufferfrompollinationfailure,iftheir
handlingrequirestoospecializedpollinatorsthatarerareorforsomereason(e.g.human
impact)becomelost,oriftheydependonlarge-sizedpollinatorsthatarenaturallylessabun-
dantoronpollinatorswithfluctuatingpopulationsoverspaceandtime.Particularlyforrare
plants,pollinationfailuremaybecritical,becausetheseplantsaremorelikelytobepollenlim-
itedduetoco-floweringspeciescompetingforlimitedpollinatornumbers[9,10].Thevulnera-
bilityofplantspeciescausedbythelackofpollinatorshasbeenlongdiscussedthroughthe
prismoftheplants’interspecificcompetitionforsharedpollinators([11]andreferences
therein,[12–14]).Theimportanceofthisproblembecomesevenmorerelevantastheconcern
forhuman-inducedbreakdownofplant—pollinatorsystemsincreases[15–21].
Hereweinvestigatewhetherplantvulnerabilitycanbepredictedbyfloralstructure(simple
tocomplex)vis-à-visotherpotentialpredictorsofvulnerability,usingasacaseexamplethe
rareandthreatenedplantsofGreece.With6600planttaxa(1072genera,185families)Greece
isregardedasahotspotforbiodiversityandendemismwithintheMediterranean[22,23].A
largenumberofthesetaxa(1462,i.e.22.15%oftheflora)areconsideredendemictoGreece
includingnumerousnarrowendemicsrestrictedtoasinglemountainorisland[23].The
endangeredGreekfloraisdescribedintwoeditionsoftheRedDataBooksofRareandThreat-
enedPlantsofGreece(hereafterGreekRedDataBook).Thefirstwaspublishedin1995with
accountsof263taxa[24].Atwo-volumebookbasedonthecurrentIUCNcriteria[1]waspub-
lishedin2009ascomplementarytothatof1995andincludedupdatesofsomeprevious
accountsplusaccountsofmanyadditionaltaxa[25].Intotal,thenumberofplanttaxa
includedintheGreekRedDataBookcorrespondstoc.7%oftheGreekflora,whilehalfofthe
country’sendemic,rareandthreatenedplantshavenotbeenevaluated[26].
Thisstudyaddressesthefollowingquestions:(1)Areplantswithcomplexflowerstructures
morevulnerablethanthosewithsimplerflowerstructures?(2)Areotherintrinsicfactorsasso-
ciatedwithplantvulnerability,suchaspollination-related(floweringtimes,floralcolorand
size)andlifestrategyones(lifeform,capabilityofasexualreproduction)?(3)Whatistheeffect
ofextrinsicfactors(e.g.geographical,ecological)onplantvulnerability?Floralcomplexitywas
quantifiedusingtheFloralComplexityIndexintroducedhere,i.e.anindextakingintoaccount
severalfloraltraitsrelatedtopresumedpollinatorspecialization.Wediscusstheeffectsoffloral
complexityalongwithotherfactorsshownheretoaffectplantvulnerabilityandaddressthe
necessityofjointplant—pollinatorconservationassessments.
PLOSONE|DOI:10.1371/journal.pone.0138414 September21,2015 2/18
PlantVulnerabilityIncreaseswithFloralComplexity
MaterialsandMethods
Dataset
Adatasetofintrinsicandextrinsicvariables(describedindetailbelow)wasgeneratedforthe
planttaxaincludedintheGreekRedDataBook[24,25].Thelatterwasthemainsourceof
informationforthecompilationofthedatasetwithsupplementarysourcescomprisingmajor
floristicworks[23,27–34],onlineHerbariumcollections(mainlyfromtheHerbariaB,E,K,
LD,MAICandW),originaldescriptionsoftaxaandothertaxonomicandfloristicpapers,
booksandonlinedatabases[35–58].NomenclaturewasupdatedaccordingtoAPGIII[59]for
plantfamiliesandaccordingtoDimopoulosetal.[23]forspeciesandsubspeciesconsidering
synonymiesandexcludingerroneousrecordsasreportedin[23].Wind-andwater-pollinated
taxawerealsoexcludedfromthedataset,whichfinallyincludedatotalof427planttaxa(S1
Table),allpollinatedbyinsects,theonlypollinatorsintheMediterraneanarea.
Intrinsicvariables
FloralcomplexityvariablesandFloralComplexityIndex. Weusedseveralfloralvari-
ablesshownintheliteraturetobefunctionallyimportantforpollination,whichwepresumed
tobeinvolvedinplants'selectivityforpollinatorsandthusrelatedtoplantvulnerability.These
were(1)shape,(2)depth,(3)symmetry,(4)corollasegmentation,and(5)functionalreproduc-
tiveunit.Anadditionalapproachinvolvedtheassemblingofthesevariablesintoafloralcom-
plexityindexdescribedbelow.
Floralshape.Accordingtothefunctionalshapeofflowers(oroffloweraggregationsfunc-
tioningassingleattractionunits,seefunctionalreproductiveunitbelow),taxawereassignedto
11levelsbasedontheclassificationbyFægriandvanderPijl[60],Barth[61]andPetanidou
[62].Theselevelswere:(1)bell(adownwardfacingbell-shapedflowerthattheinsectenters
withmuchofortheentirebody,notonlyproboscis);(2)brush(asinglefloweroraflower
aggregationwithnumerousprotrudinganthers);(3)disk(ashallowflowerwithpetalsmoreor
lessspreadoutinaflatcircle);(4)tube(atubularflower);(5)disk-tube(aflowerwithaflat-
tenedpartabruptlyarisingonatubularstalk);(6)funnel(anupwardfacingfunnel-shaped
flowerthattheinsectenterswithmuchofortheentirebody);(7)flag(the“butterfly”-shaped
floweroftheFabaceaeandPolygalaceae);(8)gullet(aflowerwithalipservingasalanding
platformforinsectstoinserttheirheadorwholebodyintothecorollatube);(9)head(a
densely-packedfloweraggregationwithmoreorlesssphericalorflatappearance;(10)lip(an
orchidflowerwithanextendedlipusedbyvisitinginsectsasalandingplatform);and(11)trap
flowers(abowlormorecomplicatedtubularstructurewithsteepandsmoothsurfacewhere
theinsectsget“trapped”forsomeperiodoftime).
Floraldepth.Floraldepth,measuredaslengthofthecorollatube,expressestheaccessibility
ofnectarrewardaccumulatedinthebottomoftheflowertubetoaflowervisitorstandingat
thefreesurfaceoftheflower.Planttaxawereassignedtothreelevels,viz.thosehaving:(1)low-
depthflowers,i.e.withcorollatubelength<4mm,includingthosewithoutfloraldepth(disk,
brushflowers);(2)medium-depthflowers,withcorollatubelength4–10mm;and(3)high-
depthflowers,withcorollatubelength>10mm[62].Particularlyinflagflowersthedepthwas
expressedasthelengthofthekeel,intrapflowers(Araceae)asthelengthofthespathetube,
andinspurredflowers(e.g.taxaofViolaceae,Fumariaceae,Ranunculaceae,Orchidaceae)as
thelengthofthespur.
Floralsymmetry.Taxawereassignedtotwolevelsbasedonthenumberoffloralsymmetry
axes,viz.thosehaving:(1)severalaxes(radialsymmetry);and(2)oneaxis(bilateral
PLOSONE|DOI:10.1371/journal.pone.0138414 September21,2015 3/18
PlantVulnerabilityIncreaseswithFloralComplexity
symmetry).FloralsymmetryinAsteraceaewasestimatedforthewholeinflorescence(seefunc-
tionalreproductionunitbelow).
Corollasegmentation.Threedegreesofcorolla(orperianth)segmentationwereconsidered:
(1)sympetaly,whenpetals(orperianthsegments)arefusedalongtheirentirelength;(2)chori-
petaly,whenpetals(orperianthsegments)arecompletelyfree;and(3)semichoripetaly,when
petals(orperianthsegments)arefusedtosomedegree,formingamoreorlessdistinctcorolla
tubewithfreelobes.Calyxsegmentationwasnotconsidered.
Functionalreproductiveunit.Thiscorrespondstotheinflorescenceandincludesflower
aggregationsfromafunctionalratherthanamorphological(planttaxonomy)viewpoint[62].
Taxawereassignedaccordinglytothreelevels,describedashaving:(1)singleflowers,including
anytypeofinflorescencewithuptofiveconcurrentlyfunctional(open)flowers;(2)aggrega-
tionsofflowersarisingonaflatorsphericalsurfaceoftheplant(heads,umbels,corymbs);and
(3)aggregationsofflowersarisingalongacylindricalsurfaceoftheplant(spikes,racemes,
panicles).
TheFloralComplexityIndex(FCIhenceforth)considersfloralcomplexityastheplants'
“selectivity”forpollinatorsandisbasedonthefivefloralvariablesdescribedabove.Eachvari-
ablewasgivenaweight(w)basedonitspotentialcontributiontofloralcomplexity:highfor
floralshape(w =0.3);moderatefordepth,symmetryandcorollasegmentation(w =
shape depth
w =w =0.2);andlowforfunctionalreproductiveunit(w
symmetry corollasegmentation functionalrepro-
=0.1).Thesumofthefiveweightsequals1.Eachlevelofthevariablesdepth,symme-
ductiveunit
try,corollasegmentationandfunctionalreproductiveunitwasassignedavalue(V)basedona
scalefrom1to3,where1indicatesalessspecializedtraitand3amorespecializedtrait.Forflo-
ralshape,duetogreaternumberoflevels(i.e.shapetypesofdifferentlevelsofdifficulty),values
(V)wereassignedbasedonascalefrom1to5.Eachvariablelevel’svalue(V)wasthemeanof
assignedscoresbyfourpollinationexperts(seeS1Text).Thefinalweightofeachvariable
definingitscontributiontotheindexwasthencalculatedbymultiplyingthevariable’sweight
(w)bythevariablelevel’svalue(V)(Table1).TheFCIforeachtaxonwasfinallyexpressedas
thesumoffinalweightsofthefivevariables:FCI=∑(w (cid:1)V ),wherew =theweightoftheflo-
j ij j
ralvariablejandV =thevalueofthefloralvariablejfortaxoni.Forexample,theFCIvalueof
ij
ataxonwithracemesofgullet-shapedflowers(i.e.bilaterallysymmetricalandpartlyfused)
andalong(>10mm)floraltubewouldbethesumofthesefinalweights:FCI=0.30+1.13
+0.60+0.40+0.60=3.03(seeTable1).TheFCIvalueassignedtoeachtaxonofthedatasetis
giveninS1Table.
Otherintrinsicvariables. Floralcolor.FivelevelswereadoptedaccordingtoPetanidou
andLamborn[63]:(1)white;(2)yellow;(3)violet,purple,pink,red;(4)blue;and(5)green.In
casesoftwoormoreconcurrentcolors,thedominant(>50%offlowersurface)wasselected,
andintaxawithindividualsbearingflowersofdifferentcolorsthemostfrequentwastaken.
Floralsize.Thiswasexpressedasthelength—widthaverageoftheexposedsurfaceofthe
corollaina2D-projection(correspondinge.g.tothefloraldiameterformoreorlesscircular
flowers).Taxawereassignedtothreelevels:(1)small,1–10mm;(2)medium,10–20mm;and
(3)large,>20mm[62].Incasesofstronglycompactinflorescences,whichgivethe“impression
offunctionallysingleflowers”,e.g.headsandcompoundcorymbsofAsteraceaeorcompound
umbelsofApiaceae,floralsizewasmeasuredforthewholeinflorescence.
Floweringseason.Threefloweringseasonswereconsidered:(1)FebruarytoMay;(2)June
toSeptember;and(3)OctobertoJanuary.Whenthefloweringtimeofataxonfellintotwodif-
ferentseasonsitwasassignedtothedominantone(biggestoverlap).Ifataxonfellequallyin
twoseasonsitwasassignedtotheearliest.
Floweringduration.Thetotalnumberofmonthsduringwhichataxonhasbeenreportedto
beinflower.
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PlantVulnerabilityIncreaseswithFloralComplexity
Table1. WeightsofthefloralvariablesusedintheFloralComplexityIndex.FordetailsontheestimationofthevariablelevelvaluesseeS1Text.
Alltermsareexplainedinthetext.
Floralvariable(w:variableweight) Levelortrait Levelvalue(V)a Finalweightb
Shape(w=0.3) bell 3.33 1.00
brush 3.50 1.05
disk 1.00 0.30
tube 3.25 0.98
disk-tube 2.75 0.83
funnel 2.65 0.80
flag 4.25 1.28
gullet 3.75 1.13
head 2.25 0.68
lip 4.50 1.35
trap 4.25 1.28
Depth(w=0.2) low-depth 1.00 0.20
medium-depth 2.00 0.40
high-depth 3.00 0.60
Symmetry(w=0.2) bilateral 3.00 0.60
radial 1.13 0.23
Corollasegmentation(w=0.2) sympetalous 2.50 0.50
semichoripetalous 2.00 0.40
choripetalous 1.50 0.30
Functionalreproductiveunit(w=0.1) single 1.50 0.15
spikes/racemes 3.00 0.30
heads 1.50 0.15
aBasedonascaleof1–3(forfloraldepth,symmetry,corollasegmentationandfunctionalreproductiveunit)orascaleof1–5(forfloralshape).SeeS1
Text.
bResultingfromthefloralvariableweight(w)multipliedbythevariablelevel’svalue(V).
doi:10.1371/journal.pone.0138414.t001
Lifeform.TaxawereassignedtofourgroupsaccordingtoPetanidouetal.[64]:(1)thero-
phytes,i.e.annualplantsthatsurviveunfavorableseasonsintheformofseeds;(2)geophytes,
i.e.perennialplantsthatsurviveunfavorableseasonsintheformofundergroundstorage
organs(bulbs,tubers,corms,rhizomes);(3)herbaceousperennials,i.e.perennialplantsthat
areentirelyherbaceousabovethegroundoronlywoodyatthebase;and(4)woodyperennials,
i.e.perennialplantsmoreorlessentirelywoody.
Asexualreproduction.Taxawereclassifiedasknownornotknowntoreproducebyvegeta-
tivemeans,e.g.bulbs,tubers,corms,rhizomes,stolons,suckers.
Extrinsicvariables
Habitat. Taxawereassignedaccordingtothehabitatstheyoccurin.Thiswasbasedon
habitatassociationsdescribedinDimopoulosetal.[23]as:(1)aquatic(freshwater)habitats;
(2)cliffsandotherrockyhabitats;(3)lowlandtomontanegrasslands;(4)high-mountainvege-
tation;(5)coastalandmarinehabitats;(6)phrygana(lowscrubland);(7)agriculturaland
ruderalhabitats;and(8)woodlandsandscrub.Whenmorethanonehabitatwasprovidedfor
ataxon,thedominanthabitataccordingtotheRedDataBookdescriptionwasretained.
Minimumaltitude. Thisdenotestheminimumaltitude(m),whereataxonhasbeen
recorded.
PLOSONE|DOI:10.1371/journal.pone.0138414 September21,2015 5/18
PlantVulnerabilityIncreaseswithFloralComplexity
Maximaldistance. Aquantitativemeasureofrange,denotingtheEuclideandistance(in
km)betweenthemostdistantlocalitiesofataxonasprovidedintheRedDataBookdotmaps.
ForitsmeasurementwedigitizedthemapsfromtheRedDataBookinArcGIS9.3(ESRI),con-
sideringalsorecentupdatesindistributionsofthetaxabyDimopoulosetal.[23].
Range-restrictedstatus. Accordingtothisqualitativemeasureofrangeintroducedby
Dimopoulosetal.[23],taxawereassignedtotwolevels:(1)range-restricted,i.e.taxawithadis-
tributionareawhoselongestdimensiondoesnotexceed500km[23];and(2)notrange-
restricted.Thisvariablewasselectedinsteadofendemismasnon-affectedbycountryborders.
Phytogeographicalregion. Taxawereassignedtothethreephytogeographicalregionsof
GreecesensuBrummitt[65]:(1)Kriti—Karpathosgroup;(2)EastAegeanIslands;and(3)
remainingGreece.Whenataxonfellintomorethanoneregion,itwasassignedtotheonewith
thehighestnumberoflocalitiesitwasrecordedin.Ifataxonoccurredinequalnumbersof
localitiesinmorethanoneregion,itsextentofoccurrence(sensuIUCN[1])ineachregionwas
additionallyestimatedandthetaxonwasconsequentlyassignedtotheregioninwhichits
extentofoccurrenceislarger.
Dataanalysis
Thepossibleoutcomesoftheresponsevariable“plantvulnerability”wereexpressedbythe
IUCNcategoriesasgivenforeachtaxonintheGreekRedDataBook,updatedwhereapplicable
accordingtotheIUCNRedListofThreatenedSpecies(www.iucnredlist.org)andaggregated
intwogroups:(1)“Lessthreatened”,includingVulnerable(VU),NearThreatened(NT),Rare
(R)andLeastConcerned(LC)taxa;and(2)“Morethreatened”,includingCriticallyEndan-
gered(CR),Endangered(EN)andpresumedExtinct(EX)taxa.IncontrasttotheIUCN
approach[1],i.e.assemblingVUtogetherwithCRandENtaxaina“threatened”group,we
adoptedastricterdistinctionamong“lessthreatened”and“morethreatened”taxa,withVU
taxaplacedinthefirstgroup.Thiswasalsonecessaryinordertoavoidpotentialinconsistency
inourdatasetthatmightarisefromthepresenceoftheoldIUCNcategory“R”oftheplants
drawnfromthe1995RedDataBook[24]:whenpullingthedataoutofbothRedDataBooks
[24,25]werealizedthatassigningataxonasRin[24]occasionallyappearedtooverlapwith
thatforVUascurrentlyformedin[1]andasusedinthe2009RedDataBook[25].
AGeneralizedLinearModel(GLM)wasfittedinR3.1.1[66]usingthe‘glm’functionwitha
binomialprobabilitydistribution,inordertoexploretherelationofplantvulnerabilitytothe
independentintrinsicandextrinsicvariables(maineffects).Astepwisebackwardmodelselec-
tionprocedureusingtheAkaikeInformationCriterion(AIC)wasperformedtoselectthebest
model.ThefinalmodelwasconstructedonthebasisoftheAIC.Asisthecasewithbinary
traitsinlogisticGLM,goodness-of-fitinthefinalmodelwastestedgraphicallywithvalidation
plotsoftheempiricalprobabilitieswiththeirstandarderrors[67].Allindependentvariables
werecheckedforcollinearitybeforeregressionanalysis.Inordertotestfortheeffectsofeach
levelofthecategoricalindependentvariablesonplantvulnerability,weranthe‘glm’function
foreachlevelseparatelyandcalculatedthesignificanceoftheireffectswiththelikelihoodratio
chi-squaretestsofthedevianceanalysis.
InordertocheckforthepotentialeffectsofthecomponentsoftheFCI(viz.floraldepth,flo-
ralshape,floralsymmetry,functionalreproductiveunit,andcorollasegmentation),wecon-
ductedthefollowingsteps:Weran(1)bivariatetestswheretheeffectsofeachoneofthesingle
floralcomplexitycomponentsandofFCIitselfweretestedindividually(S2Text);(2)afull
GLMmodelwithallindividualintrinsicvariablesincludingfloralcomplexitycomponents(viz.
floraldepth,floralshape,floralsymmetry,functionalreproductiveunit,corollasegmentation,
floralcolor,floralsize,floweringduration,floweringseason,lifeformandasexual
PLOSONE|DOI:10.1371/journal.pone.0138414 September21,2015 6/18
PlantVulnerabilityIncreaseswithFloralComplexity
reproduction)andtheextrinsicones(viz.habitat,minimumaltitude,maximaldistance,range-
restrictedstatusandphytogeographicalregion)(S2Text);(3)aGLMmodelwitheachsingle
floralcomplexitycomponentandallotherintrinsicandextrinsicvariables(S2Text);(4)the
GLMwiththefloralcomplexitycomponentsreplacedbytheFCIitselfinthefullmodel.
Beforechoosingourstandardnon-phylogeneticstatisticalmodelingapproach,wetested
ourdatasetforphylogeneticdependenceregardingthevulnerabilityoftheplants.Thephylog-
enyofthe427plantsofourdatasetwasconstructedaccordingtoAPGIII[59]usingtheonline
softwarePhylomaticv3[68].Thebranchlengthsofthisphylogenetictreewereadjustedsoas
tocorrespondtoevolutionarydivergencetimebetweenclades,usingthe‘bladj’algorithmin
thesoftwarePhylocomv4.2[69].Forthiscalibration,weusedtheupdatednodeagesprovided
byGastauerandMeira-Neto[70],whichaddresstheinconsistenciesobservedinthedefault
agesfileofPhylocombasedonWikstrom’sdatingofAngiospermfamilies[71].Aphylogenetic
tree(Fig1)wascreatedusingtheweb-basedInteractiveTreeofLifev2[72].Boththeraw
responsevariableanditsresidualsinthefinalmodelweretestedforphylogeneticsignal(see
[73]andreferencestherein).Toestimatethephylogeneticsignal,i.e.totestwhetherplantvul-
nerabilityfollowsarandomphylogeneticpatternoritisphylogeneticallyclumpedcorrespond-
ingtoaBrownianmotionmodel,wemeasured(i)fortherawvariable,theDstatisticfor
binarytraits,whichisbasedonthesumofthesister-cladedifferencesofthegiventraitina
phylogeny[74]usingthe‘phylo.D’functionintheRpackagecaper0.5.2and(ii)fortheresidu-
als,bothBlomberg’sK[75]andPagel’sλ[76]usingfunctions‘phylosignal’intheRpackage
picante1.6–2and‘pgls’(byfittingthemodel:vulnerability~1)incaper0.5.2.Allmetrics
revealednosignificantphylogeneticsignalofplantvulnerability(seeS3Text),allowingusto
proceedwiththeabove-mentionedGLMapproach.
Results
FloralComplexityIndex
TheFCIscoresforthe427taxaexaminedvariedbetween1.15and3.25.Thelowestscore
(1.15)wasrecordedforseveralplantsineightfamilies(e.g.Papaveraceae,Geraniaceae,Paeo-
niaceae),whilethehighest(>2.50)forplantsofAraceae,Fumariaceae,Orobanchaceae,Faba-
ceae,Orchidaceae,Lamiaceae,Polygalaceae,LentibulariacaeandViolaceae.Twosubspeciesof
theorchidDactylorhizakalopissii,subsp.kalopissiiandsubsp.pythagorae,designated,respec-
tively,asEndangeredandCriticallyEndangered,obtainedthehighestcomplexityscoreof3.25
(Fig1;S1Table).
Plantvulnerability
BivariatetestsfortheeffectsofeachofthecomponentsoftheFCIshowedthatnosinglefloral
complexitycomponent(viz.floralshape,floraldepth,floralsymmetry,corollasegmentation,
functionalreproductiveunit)isasourceofvariationforplantvulnerability(S2Text).When
componentswereindividuallyenteredinthefullGLMincludingallotherintrinsic(viz.floral
color,floralsize,floweringduration,floweringseason,lifeform,asexualreproduction)and
extrinsicfactors(viz.habitat,minimumaltitude,maximaldistance,range-restrictedstatus,
phytogeographicalregion),wefoundseparatestatisticallysignificanteffectsonlyfortwocom-
ponents,i.e.floralsymmetryandfunctionalreproductiveunit.Whenallsinglefloralcomplex-
itycomponentswereenteredtogetherinthefullmodel,onlyfloralsymmetryshoweda
significanteffect(S2Text).Morespecifically,taxawithradiallysymmetrical(actinomorphic)
flowersshowedanegativecorrelationtovulnerability(vulnerability~radialfloralsymmetry
estimate:-0.86,z-statistic=-2.95,p-value=0.003).Consequently,eachdimensionoffloral
complexityalonedoesnotseemtobeapredictorofplantvulnerability,andfloralsymmetryis
PLOSONE|DOI:10.1371/journal.pone.0138414 September21,2015 7/18
PlantVulnerabilityIncreaseswithFloralComplexity
Fig1.TheFloralComplexityIndex(FCI)valuesdistributedacrosstheGreekrareandthreatenedplants’phylogeny.Greybarsindicatetherelative
magnitudeoftheFCI(highestvalue:3.25,lowest:1.15).Redrectanglesmarkthe“morethreatened”(CR,ENorEX)taxa.
doi:10.1371/journal.pone.0138414.g001
thestrongestpredictorofallthecomponentswhenaddedtothemultivariatemodel.Lastly,we
comparedtwofullmodelsincludingeithersymmetryorFCIplusallotherintrinsicandextrin-
sicfactorsmentionedabove;wefoundthatthemodelincludingFCIperformedbetterthanthe
modelincludingsymmetrybasedonAICandtheBayesianInformationCriterion(S2Text).
OurfinallytestedGLMincludedFCIplusallotherintrinsicandextrinsicfactorsasinde-
pendentvariables.BasedontheAICstepwisebackwardmodelselectionthebestfittingmodel
includedFCI,lifeformandfloralcoloramongtheintrinsicfactors;andmaximaldistance,hab-
itatandminimumaltitudeamongtheextrinsicones(Table2).Thevariablesasexual
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PlantVulnerabilityIncreaseswithFloralComplexity
Table2. Resultsofthebestfitting(basedonAIC)GLMshowingtheeffectsoftheintrinsicandextrinsicvariablesontheGreekrareandthreatened
plants’vulnerability.
Independentvariables LRχ2 Df P-value
Intrinsic Lifeform 10.183 3 0.0171
Floralcolor 8.602 4 0.0719
FloralComplexityIndex 10.230 1 0.0014
Extrinsic Habitat 18.129 7 0.0114
Minimumaltitude 3.012 1 0.0826
Maximaldistance 12.683 1 0.0004
doi:10.1371/journal.pone.0138414.t002
reproduction,floweringseason,floweringduration,floralsize,phytogeographicalregionand
range-restrictedstatuswerenon-significantandthusdiscardedfromthefinalmodelbasedon
theAIC.
ThemeanFCIwasfoundtobesignificantlyhigherinthe“morethreatened”thanthe“less
threatened”taxa(Fig2a).Boththeseplantgroupsarecharacterizedbythehighproportionof
herbaceousperennialsandgeophytesbutdiffersignificantlyintheproportionofwoodyperen-
nials(higherinthe“lessthreatened”);thepresenceoftherophytesisslightlyhigherinthe
“morethreatened”thaninthe“lessthreatened”group,albeitwithoutsignificantdifference
(Fig2b).Amongallvariablesexamined,maximaldistancebetweenataxon’smostdistantpop-
ulationswasfoundtobethemostsignificant(Table2)withthismeasureofmaximumrange
beingsmallestinthe“morethreatened”comparedtothe“lessthreatened”plants(Fig3a).Both
plantgroupsoccurinallhabitatcategories,withthe“morethreatened”beingsignificantly
morefrequentincoastalhabitats.“Morethreatened”taxatendtobemorefrequentinruderal
habitats,whereas“lessthreatened”aremorelikelytobeencounteredincliffs,woodland/scrub
andhigh-mountainhabitats—althoughthesedifferenceswerenotstatisticallysignificant(Fig
3c).Floralcolorandminimumaltitude,althoughpresentinthebestmodel,havep-valuesmar-
ginallyoutsidethesignificancelevel(Table2)andsodonotdifferbetweenthetwoplant
groups(Figs2cand3b).
Discussion
Effectsofintrinsicfactorsonplantvulnerability
Amongallfloralvariablesexamined(viz.FCI,floralsize,floralcolor,floweringdurationand
season),theFCIwasfoundtobethemostpredictiveforataxon’svulnerability:taxawithhigher
floralcomplexityaremorelikelytobemorethreatened.Apossibleexplanationforthismaybe
pollinationlimitation;suchlimitationmaybeduetospecializedpollinatorscarcityortothelim-
itedattractionbythesmallpopulationsizesthreatenedplantsnormallyoccurin[16,77].
Akeyrolemaybeattributedtofloralsymmetry,whichwastheonlyoneamongFCIcompo-
nentshavingperseasignificanteffectonplantvulnerability.The“morethreatened”plants
examinedherewerefoundtohavemorefrequentlybilaterallysymmetricalflowers(44.3%of
the“morethreatened”plants)comparedtothe“lessthreatened”(28%).Bilateralfloralsymme-
tryissuggestedtoprovidemultipleadvantagesforaplant,suchashighervisitation,moreeffi-
cientrecognitionandfasterhandlingbypollinatorsandhigheroutcrossingratesthanradial
symmetry[78–80].Moreover,inacommunitycontextfloralsymmetryhasbeenshowntopre-
dictdifferencesinpollinatorvisitationwithinaplant—pollinatornetwork[81].However,bilat-
eralsymmetrymightalsoturnintoadisadvantageintimesthatpopulationsofassociated
specializedpollinatorsdecline[78].Furtherthanfloralsymmetryhavinganimportanteffect
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PlantVulnerabilityIncreaseswithFloralComplexity
Fig2.IntrinsicvulnerabilityfactorsoftheGreekrareandthreatenedplants.Effectsoftheintrinsicvariablesonplantvulnerabilityasincludedinthebest
fittedlogisticGLMbasedonthebackwardAICselectionprocess.(a)MeanvalueoftheFCI(±SE);(b)lifeform;and(c)floralcolor.Categoricalindependent
variables(b,c)arepresentedinspinograms.Thewidthofthecolumnscorrespondstotherelativefrequencyofthe“morethreatened”and“lessthreatened”
plantsinthedataset;theheightsofthecellsrepresenttherelativefrequencyoftheresponsevariableineveryleveloftheexplanatoryvariables.Coloredcells
denotestatisticalsignificanceoftherespectivelevel(**:(cid:3)0.01,***:(cid:3)0.001).
doi:10.1371/journal.pone.0138414.g002
onplantvulnerability,thehighersignificanceoffloralcomplexityvs.thatofitsindividualcom-
ponentsimpliesthatflowercomplexityisamoremeaningfulpredictor,andwhenconsidered
togethernotonlythesymmetrybutalsotheshapeanddepthoftheflowers,theirsegmentation
andtheiraggregationininflorescencesareinfluentialforplantvulnerability.Evidencefrom
empiricalstudiespointstowardsthesamedirection.Forexample,ithasbeenfoundthatsym-
petaloustubular(deep)flowers,whosehandlingrequirespollinatorswithlongmouthparts,
receivefewerinsectvisitsthanopenchoripetalousflowers[82],thelatterbeingmorecom-
monlyvisitedbyinsectsthatarelessspecialized[83].Likewise,plantspecieswithcomplexflo-
ralshape(e.g.flagorgullet)wereshowntodependonspecializedpollinatorbehavior
comparedtospecieswithlesscomplexflowers(e.g.diskorhead),whichhaveamoregeneral-
izedpollinationsystem[82].Finally,theorganizationoffloralreproductiveunitsatdifferent
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