A test of community re-assembly using the exotic communities of New Zealand roadsides, in comparison to British roadsides.

A test of community re-assembly using the exotic communities of New Zealand roadsides, in comparison to British roadsides.
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  A Test of Community Reassembly Using the Exotic Communities of New Zealand Roadsides inComparison to British RoadsidesAuthor(s): J. Bastow Wilson, John B. Steel, Mike E. Dodd, Barbara J. Anderson, IsoldeUllmann, Peter BannisterSource: Journal of Ecology, Vol. 88, No. 5 (Oct., 2000), pp. 757-764Published by: British Ecological Society Stable URL: Accessed: 26/06/2011 07:14 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at . JSTOR's Terms and Conditions of Use provides, in part, that unlessyou have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and youmay use content in the JSTOR archive only for your personal, non-commercial use.Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at . . Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printedpage of such transmission.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact  British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to  Journal of  Ecology.  JournalfEcology 000, 88, 757-764 t92000BritishEcologicalSociety Atestof communityeassembly sing heexoticcommunitiesf New ZealandroadsidesncomparisonoBritish oadsides J. BASTOW WILSON,JOHN B. STEEL, MIKE E. DODD,BARBARAJ.ANDERSON,ISOLDEULLMANNtand PETERBANNISTER BotanyDepartment, niversityfOtago,POBox 56, Dunedin,NewZealand;*Biologyepartment, penUniversity, iltonKeynes,MK76AA,UK;andtLehrstuhlfidrotanikI, Universitdturzburg,-97082Wuirzburg,ermany Summary 1 Competing heories fcommunity ssemblyreverydifficulto test.Fourmaintheories xist. The Stochasticheoryeesspeciesassemblysbeingrandom. TheHumptyDumpty/Alternativetable StatesASS) theory uggestshatcommunitymay be unable toreassemble tselfromtsconstituentpecies. The Deterministictheory uggestsherewillbeconvergenceo one stable state. ThePre-adaptationtheory s similar othe Deterministicheoryut emphasizes hatmany speciesfitthestable tatebecauseof characters cquiredelsewhere.2Thereassemblyfa flora nto newcommunitiesn adifferentountry,ritsassimilations amajor componentof suchcommunities,ffersmeans to test thesetheories. heinvasionofBritish lant species nto NewZealand, andtheirreassemblyntoroadside communities here,sa good exampleof such a naturalexperiment.3Plantcommunitiesf NZroadsides were comparedto the communitiesftheBritishNational Vegetation ClassificationNVC). Britishroadsidecommunitieswere alsocomparedo the NVC as a control.New Zealand roadside communitiesprovidedfit o theNVC communitiesfonly 54.7% onaverage.Afterxcludingspecieshat re notpresentnNZ,and thereforeould notpossiblyeassemble,hefit ncreased o61.1%.British oadsidesgavea 65.8% fit.TheNZfiguresresimi-lar to the fitbtainedwithrandomdata (58.7%), indicatinghattheNZcommu-nitiesearittleelationo theonesformed ythe samespeciesnBritain.4Similarityetweenroadside communitiesn NZandBritainwaslow, formingtwo almostdistinct etsofcommunities.5 Some ofthepredictionsoftheStochastic, HumptyDumptyASSandDeterministic odels are borneout,but othersrenot. t isconcludedhat Britishspecieshave reassembled nto communitiesn NZmostof which renew,.e. dis-tinctfrom hose that occur nthe nativerangeofthespeciesnBritain.The evi-dencepointso aprocessofcommunityssembly y pre-adaptation. Key-words. alternativetablestates, ssemblyules, ommunityeassembly,eter-ministictructure,xoticspecies, HumptyDumpty effect,nvasion,NVC, pre-adaptation, oadside,tochasticmodel Journalof Ecology (2000) 88, 757-764 Correspondence: .B. Wilsonfax +64 3479 75 83;  758Reassemnblyfroadsidelantcommunities? 2000BritishEcologicalSociety Jour7nalfEcology, 88, 757-764 IntroductionThere as been ecent ebate n the rocess f om-munityssembly:s the ommunityn any nviron- ment deterministiconsequence f physical ndbiotic ilteringKeddy 1992), re there lternativestable tates Law & Morton 993), r is composi- tion stochasticSykeset al.1994)?Thisquestionsa basicone,related o thedebate etweendherents of the ndividualisticypothesis.andsupportersof ome orm ftightlyoevolving,uperorganismic community'Underwood986).Most onsiderationf his ssuehas been heoreti-cal,orbysimulation. uh & Pimm1993)and SamuelsDrake1997)haveproposedheHumptyDumpty rinciple:hattmight otbepossible orcommunitieso reassemble rom heir & Morton1996)foundupportorthisdeafromimulationsnwhichhefinal om-munityouldnot be reassembledromts speciesalone.Thiswould eadto alternativetabletates,since he ndresultouldifferromlaceoplace,accordingowhattherpecieswereresentLaw&Morton993).Itis difficultotest these deas. Reassemblyexperimentsithmicro-organismsave runintomethodologicalroblemsDraketal. 1993;Grover&Lawton1994). Experimentsithhigher lantswould e evenmore solutions to use a naturalxperiment,here lienspecieshaveinvaded narea,mainlyrom ne sourcelora,nsufficientumberor hepossibilityfcommunityreassemblyoberealistic. uch anopportunityarisesnsouthernewZealandNZ) (Wilsontc!l.1988;Wilson1989). ManyBritishpecieshavebecomenaturalizedhereecauseofcommercial/cultural ontact,ndbecauseofsimilarityncli-mate.n somehabitats,uch smanyftheroad-sides,he ommunitiesowompriselmostntirelyBritishpecies.Roadsides re an excellent abitattypeforstudying ommunityssemblyecausemanagementssimplend ratheronsistent,nd because roadsides ct as corridorso allow optimaldispersal,minimizingheproblemof dispersal im-itation.However, he extent f community eassem-bly can be judged onlyincomparison withcommunities n the area from which the speciescame, .e.Britain.We use roadsides asatestfor community eas-sembly, omparingNZ and Britishitesby samplingthis habitatnboth countries nd using the BritishNationalVegetationClassification NVC; Rodwell1991-95)todeterminewhetherhe species in NZhave reassembled ntothesame communities s inBritain. The NVC is a classification ntended tocover ll thevegetationf Great Britain: A nationalandsystematic phytosociologicaltreatment ofBritishvegetation' Rodwell1991). It is based on35000quadrats, analysed byobjectiveprocedures,and classifiednto860communitiesnd subcommu-nities.For comparison,wealso test the fitofran-domassemblagesfspeciesotheNVC. Methods AREASANDSAMPLING The New Zealandsurveywas conducted alongroutesinsouthern South Island(Ullmann et al.1995).The area included roughly ast-west rans-ect, rangingfromcoast tocoast, passing throughthe driestartofNZ,and includinghehigh-rainfallHaastPass across the SouthernAlps.The British transectraneast-west(fromSouthwoldtoAberystwyth),assing throughthe driestpartofBritain,ndincludinghehigh-rainfalllynlimonpassin theWelsh mountains.tis verydifficultomatchclimates,ut both southernNZand BritaincomewithinategoryCbf of theK6ppenclimateclassificationBriggs&Smithson1986),and theenvironnmentalangesofthe two areasoverlap,withNewZealandtendingtoencompassthe Britishrange (Table 1). Lengthsof roadside willdiffer nthe time sincedisturbance,utroadsidesareby Table1Ranges of climateeatures cross theNew Zealand and British reassampledNew Zealand areaBritish reaElevation5-420m5-418mSlope0-450 0-450SurroundingandscapePasture,woodlandPasture,woodlandand suburban) Rainfall345-3460mm485-1777mmRainfallndriestmonth17-425mm35-97mmMeantemperaturefthe warmestmonth 12-17?C14-17 ?CMeantemperaturefthe coldestmonith 0-7?C3-4 ?CpH4.4-8.25.3-7.2Main herbivore RabbitRabbitManagementControlofwoody plantsbyControl fwoodyplantsbyoccasional spot herbicides occasionalmowing  759 J.B.Wilson et al.t)2000BritishEcologicalSocietyJournalfEcology,88, 757-764 theirnaturedisturbed uite often, nd the range oftime sincedisturbance ertainly verlaps betweenthe two countries.In NZ,three roads (Ullmann et al. 1995) weresurveyed ylocating ites t 10-km ntervals, iving68 sites. nBritain, he muchhigher ensity f roadsallowedsampling longastraight ast-west trans-ect, withpointsat 10-km ntervals, romwhich thenearest road site was sampled, giving40 sites. Inboth NZ andBritain,each site had four 2x4 mquadrats as per Wilson et al. 1996). The shoot pre-senceofallvascular plant species was recordedneachquadrat. Presence/absencenthe four uadratsata sitewas used to give a crudebut objectivemea-sure of theabundanceof that pecies t the ite. ANALYSES:BRITISH NATIONALVEGETATIONCLASSIFICATION Questionsofagreementwith the NVCconcernthebehaviournNew Zealand ofspecies that areincommonwithBritain:he Britishpecies'.Itwould be unrealistic o expect the British pe-cies to reassemble n NZ ina commnunityominatedby species notinthe British flora(mainlyNZnatives,butafew exotics fromother parts oftheworld).We thereforexcludedfromnalysesof theNZdata any site where fewer than 50% of theoccurrenceswere of Britishpecies (thisexcludedninesites, where the roadsides wereadjacenttonativeforest).We comparedcommunityampleswiththeNVC usingtheprogramTablefitHill 1989, 1996).Thecalculationsarebased on the Tablefitdatabaseofthecompositionof each NVCcommunity.hisdatabase,naturally,ontains omespecieshathavenot reachedorat leasthave not naturalizedn)NZ.It seemedunrealistic oexpect peciesto reassembleinto communities hentheywerenot presentn thecountry.Two Tablefit databases werethereforeused:Full,the normal Tablefitdatabase of Britishspecies;andNZNaturalized,heTablefitdatabasemodified o includeonly speciesthat arepresentnNew Zealand.We alsoperformednalyseswithdatabasethatincludedonly peciespresentt more than twositesinNZ.However,he resultsweredentical othosewithNZNaturalized,nd are notpresented.Bothdatabases wereused with he NZsites,butonlytheFull database withheBritishites.TableFitwas thepreferred rogramboth because of thematchingmethod t uses and becausetwaspossibleomodifyitsdatabasein thisway.TableFit calculatesheper-centageitetweenhe observed pecies ompositionand that pecified or ach NYC communityn turn,based onspecies composition nd constancy here,constancy mong the four quadrats at each site),and reports hose with the closest fits.The good-ness-of-fitf asite withfouruadrats)scalculatedas apercentageigure:Goodness-of-fit0.5xGF' + 0.5xG2'GI'=GIx(2 - G2/100)xG2/100GI(compositionalatisfaction) 100xEmin(oC,e,)/SumE c [butwithmaximum f100,and with'carryover' mechanism sexplainednHill(1989).cis theconstancy lass]SumE= e c G2'min(Gl', G2)G2(meanconstancy) 100x E(fc xoc)/ (fcxec) c [againwithmaximum f100] SumO= E?c c f,theprobabilityfoccurrenceorconstancyclass c:fI=0.12,f2=0.25, f3=0.50, f4=0.75andf5=0.95oc=thenumber fspeciesnconstancylasscin theamplee,=thenumberfspeciesnconstancylass cexpectedn theNVCcommunity =f,xN, N=the total numberofspeciesnconstancyclass c in theNVCcommunityWereporthe best-fitVCcommunity.Wealsoreport,s 'best+closesecond',theresults orthebest fitplusthe second best where thelatterwaswithin 5%fit of the best fit. ncalculatinghenumberoffits o each NVCcommunity,nd sec-ond-bestfits,onlyfits of50%or more werecounted. Thepresenceof some native NZspecies,andothersnot nativetoBritain,s notproblematicforcommunitymatchingecause the TableFit fit-tingprocesswas unaffectedythepresencef suchspecies.The British ites containedveryfewpeciesrecentlyew to Britain. ANALYSES:SIMILARITIES Similaritieswere calculatedbetween all possiblepairsof sites using the Jaccardindex (Cormack1 71). A minimum spanning tree(the shortest  760 Reassemblyfroadsidelantcommunities t)2000 BritishEcologicalSociety JournalfEcology, 88, 757-764 branching path that connects all the points;Cormack 1971) was calculatedforll sites NZ andBritain), gain using heJaccard oefficient. ANALYSES: RANDOM DATA An important riterion n udging the fitof speciesassemblagesto acommunitylassification uchasthe NVC is whether hey match the communitiesmore closely than a random assemblage of specieswould. Such an assemblagerepresents null modelof communityonstruction.Randomizationswere performednwhich peciespresenceswere allocated at random to sites. Thenumber f occurrences i.e. frequency mong sites)of a speciesnthe randomised ata was held equalto that for the species in the observed data.Similarly,ite richnesseswereretainedby holdingthe numberof speciesina sitein therandomiseddata equal to the number f species t the sitentheobserveddata. Species werellocated toquadratsat random within hese constraints, sing the nmethodof Wilson(1987).The distributionfabundances(1-4) withinachspecies washeldequalinthe ran-domizations o thedistributionn theobserved ata,but those abundanceswereallocated at randomtothesites n which hespeciesoccurred n the rando- mised data. Two thousand such random commu-nities were generated ndependently rom theNZand the British ata. Results NEW ZEALAND DATA Usingthe Fulldatabase,the mean best fit of theNew Zealand roadside sitesto the NVC was54.7%(Table 2).The most common best-fit ommunities(Table 3)wereUpland grasslandU4(Festucaovina-Agrostis apillaris-Galiurmaxatile) and Ul (Festucaovina-Agrostis apillaris-Rumnexcetosella).How-ever,the closestindividualfitswere to neitherfthese: the fourfits of75%or betterwere all toMesophytic grasslandMG6(Lolium perenne-Cynosurus ristatus).ncludinglosesecond-bestits,the same three ommunities ittedmostoften,butwith U4 and MG6 being themost common fits(Table 3).Using the TableFit database thatexcluded peciesabsentfromNZ(NZNaturalized),hemean fitofthe NZ roadsidecommunitieso the NVC increasedconsiderably Table 2).The most common best-fitcommunitieswere Upland grassland U4 (Table 3).Therewere five ites with fitsf80%ormore,allbelongingoupland grasslandU4;these sites com-prisedmainlyritishpecies. BRITAIN Themeanfit f the British oadside communitiesotheNVC was higherhan with heNZdata (Table2).ThehighestBritishfit was nobetterhanthehighestNZfit, uttherewere few poorfitsTable2).The most common best-fit ommunity y somemarginwasMesotrophicgrassland MG1(Arrhenatherumlatius; Table3), with weedy com-munity V25 (Tallherbcommunity: rtica-Cirsiumarvense) econd,withessthan halfasmanybestfits.Whenincluding closesecond-bestfits,UnderscrubW24(Rubusfruticosus-Holcusanatus)became the second mostfrequent losely fittingcommunity,elow MG1. RANDOM ASSEMBLAGES RandomisingheNZdata(andcomparingwithheNZNatu7ralizedatabase), the meanfitwas 58.7%,witharangeof across randomizations f 55.9-61.4%.The observedmeanNZvalueof61.1%washigherhan all but oneof therandomizations. hisgivesPvalueof1/2000 0.0005for 1-tailedest,or 0.001fora 2-tailedtest, highly ignificantneither ase.Randomisinghe Britishata,the fitoNVC communities asonaverage 61.9%, rangingindifferentandomization unsfrom 9.6 to 64.2%.Sincethe observedBritish alue of65.8%ishigherthananyof the2000 randomised alues,tssignifi-cantlyhigherhanexpectedtrandomP < 0.0005with 1-tailedr2-tailedest). SIMILARITIES Usingthe Jaccardmeasurerange 0-1,with1indi-cating complete similarity),hemeansimilaritybetweenNew Zealandsites0.207)wasslightlyessthan that between the British sites(0.265).Themeansimilarityetween aNZ siteand aBritishone,at0.097,wasconsiderablyower than withineithercountry.Theminimum-spanningreesepa-rated the NZ sitesfromthe Britishites,almostcompletelyFig. 1).The two exceptionswere oneNZ site (near the driestpart of the country) hatjoined the British roup, nd one British ite on theedge of the Welsh mountains) that oined to theotherBritish itesonly hrough ne NZ site.Neither Table2Percentageit of roadside vegetationocommu-nities of the BritishNational Vegetation Classification(NVC)MeanRangeinData Database fit %) fit %)New Zealand Full54.7 20-81New Zealand NZNaturalized 61.1 20-83Britain Full 65.8 44-81
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