Table Of Content©EntomologicaFennica.19March2018
Wood ant assemblages of Formica rufa group
on lake islands and in mainland woodland in Central Finland
JouniSorvari
Sorvari,J.2018:WoodantassemblagesofFormicarufagrouponlakeislands
andinmainlandwoodlandinCentralFinland.—Entomol.Fennica29:21–29.
Associationsofislandsizeandisolationontheoccurrenceandspeciesrichness
of five wood ant species of the Formica rufa group (F. rufa, F. aquilonia, F.
lugubris,F.polyctenaandF.pratensis)wastestedintheLakeKonnevesiarchi-
pelagoinCentralFinland.Inaddition,thespeciescompositionwascomparedto
thatofmainlandforestsofthesameregion.Islandisolationhadnoassociations
withthewoodantoccurrenceinthisarchipelago,butformostspecies,increasing
islandsizewaspositivelyassociatedwiththeoccurrenceprobability.According
tothefindingsamongthefivespecies,Formicalugubrisisthebestadaptedfor
insularliving.Therewasapositivespecies–arearelationshipasthespeciesrich-
nessofwoodantsincreasedwithanincreasingislandsize.Theislandcommunity
ofwoodantswasdominatedbycoloniesofthemonogynous(singlequeen)spe-
cieswhereasthemainlandcommunitywasdominatedbythoseofpolygynous
(multiplequeen)species.
J.Sorvari,DepartmentofEnvironmentalandBiologicalSciences,Universityof
EasternFinland,P.O.Box1627,FI-70211Kuopio,Finland(currentaddress);
DepartmentofBiology,SectionofEcology,UniversityofTurku,FI-20014Turku,
Finland;E-mail:[email protected]
Received24January2017,accepted3May2017
1.Introduction
Ideally, island biogeographical studies are
conductedwithasetofspeciesrepresentingsimi-
Accordingtoislandbiogeographytheory(Mac- larlifehistorystrategies,forexampleagroupof
Arthur & Wilson 1967), a large island should closelyrelatedspecies.Anexampleofthiskind
havehigherspeciesrichnessthanasmallisland ofaspeciesgroupistheEuropeanmound-build-
(with all remaining independent variables ingwoodantsoftheFormicarufagroup.Itcon-
equals).Thismaybeduetothefactthatlargeis- sistsofsixcloselyrelatedspeciesbelongingtothe
landsmayhavemoreecologicalnichesandthat subgenusFormicas.str.,namely:Formicarufa
the large surface itself eases colonisation. This Linné, 1761; F. aquilonia Yarrow, 1955; F. lu-
should also be visible on an individual species gubris Zetterstdt, 1840; F. paralugubris Seifert,
level as a species’ probability of occurrence 1996;F.polyctenaFörster,1850andF.pratensis
wouldbehigheronlargeislands.Numerousstud- Retzius,1783.ApossibleseventhEuropeanspe-
iesshowahighernumberofspeciesonlargeis- cies has been recently reported to exist in the
lands compared to smaller ones (e.g. Morrison SwissAlps(Bernasconietal.2011).Thesespe-
1997,Rizalietal.2010,Clarketal.2011,Morri- ciesoccurmostlyinconiferforestsorforestmar-
son2016). gins, although F. pratensis also commonly oc-
22 Sorvari (cid:127) ENTOMOL.FENNICAVol.29
cupymeadowsorotheropenareas(Collingwood woodantsgenerallypreferredlargeislandsover
1979, Rosengren & Pamilo 1983). Five of the smallerislandsintheBalticSeaarchipelagosince
species live in Finland. The most common spe- large islands have increased cover of suitable
ciesareF.aquiloniaandF.lugubris,whichseem habitats.
toliveinallregionsinFinland.Therest,F.rufa, ThespeciesofF.rufagrouparespecialistsof
F. polyctena and F. pratensis, are generally re- latesuccessionforests,especiallythepolygynous
stricted to the southern part of the country (e.g. speciesF.aquiloniaandF.polyctenathattendto
Stockanetal.2016). nestinlargematureforests(Rosengren&Pamilo
Thecoloniesarepopulousastheworkerpo- 1983).Monogynousspeciesgenerallypreferfo-
pulationrangesfrom100,000toseveralmillion restsandforestedges,butareabletocolonisefo-
inamaturecolony,dependingonthespeciesand rests of younger successional stages than the
thecolonystructure(Collingwood1979,Rosen- polygynousspecies(Punttila1996).
gren & Pamilo 1983, Seifert 1991). Within the On a local scale, such as in an archipelago,
group,F.aquiloniaandF.polyctenaareobligato- factorsinfluencingtheislandbiogeographyofthe
rily polygynous(i.e.therearealwaysseveralto woodantspeciesoftheF.rufagroupcouldbeis-
thousandsofegg-layingfemalesinacolony)and landsize,isolationandhabitattype(e.g.forested
they are normally polydomous, in other words vs.rocky).Inforestedislandsofthisstudy,Iin-
they haveseveralcoloniesinanon-competitive vestigated 1) whether isolation and island size
relationship, peacefully sharing the resources haveadifferentassociationwiththeoccurrence
(Collingwood1979,Rosengren&Pamilo1983). ofwoodantsthatusedifferentstrategies(mono-
Theothers,F.rufa,F.lugubrisandF.pratensis, gynyandpolygyny)and2)whetherwoodantas-
seem to be facultatively polygynous, in other semblages have a different species composition
wordstheycanswitchtacticsfrommonogyny(a on islands compared to that of the surrounding
singleegg-layingfemaleinacolony)andmono- woodlandassemblagesonthemainland.
domy(acolonyinhabitingasinglenest,aggres-
sive to all aliens and conspecifics) to polygyny
2.Materialsandmethods
andpolydomy(Rosengrenetal.1993).InFinn-
ish populations, however, they all tend to be
monogynous or at least monodomous (Rosen- Asampleof74forestcoveredislandsofvarious
gren&Pamilo1983,Rosengrenetal.1993). sizes and 133 forest stands were surveyed on
Allspeciesofthegroupestablishnew colo- westernpartoftheLakeKonnevesiandtheadja-
nies by dispersal flight followed by a colony cent mainland around Konnevesi Research Sta-
foundingbymeansoftemporalsocialparasitism, tion(theUniversityofJyväskylä;WGS84coor-
i.e. the dispersing queen takes over a colony of dinates:N62°36.9570’,E26°20.7972’)incen-
oneofthespeciesofthesubgenusServiformica, tralFinlandduring1999–2001.Woodandwork-
e.g. F. fusca Linnaeus or F. lemani Bondroit; ers(10–30/nest)weresampledfromthetopofall
however,polygynouscoloniesareabletoestab- nest mounds found in the study area. The ants
lishnewnestsbycolonybudding(Rosengren& were stored in 70% ethanol. Species identifica-
Pamilo1983).Thetendencyforshort-rangedis- tion was based on the keys of Collingwood
persalinconnectionwiththetendencyofcolony (1979) and Douwes (1995) and on ten workers
splitting in polygynous species may affect the fromeachcolony.Allfivewoodantspresentin
dispersalandcolonisationabilityofspecies.Ina Finlandwerefoundinthestudyarea,butonlyone
studybyMabelis(1994),ithasbeenshownthat nestofF.pratensis(Table1).
polygynous F. polyctena was common in large The nearest distance from the island to the
forest patches whereas smaller, isolated forest mainland(nearestmainlanddistance:NMD)and
patches were typically dominated by mono- thenearestdistancetoanywoodlandcoveredter-
domous F. rufa. In the same study, it was also restrial biome, mainland or island (but not tree-
shownthatlargerforestpatcheshadmorespecies lessrockyislets)(ND),weremeasured.Connec-
of wood ants than smaller patches. In addition, tivitywascalculatedasthemeanofintotalthree
Vepsäläinen and Pisarski (1982) showed that NMDsand/orNDs.Ifanislandwaslocatedina
ENTOMOL.FENNICAVol.29 (cid:127) Woodantsonislands 23
Table1.Numbersofislandsandforestplotssettledby us) from 1999 to 2000 (e.g. Jäntti et al. 2007).
woodantspecies(withexpectedfrequencybasedon Withineachstudystand,acircularstudyplotofØ
totalfrequenciesinparentheses)onLakeKonnevesi 100mwassearchedforwoodants.Theminimum
islands(N=74)andinmainlandforestsof
distancesbetweenneighbouringstudyplotsvar-
Konnevesi–Laukaaregion(N=133)inCentralFin-
ied between 233 m and 3,905 m (mean ± SD:
land.P=polygyny,M=monogyny.Inthelowerpartof
1,054.0m±690.4).Thestudyplotsweredistrib-
thetable,speciesusingapolygynystrategyand
utedonalandscapeof1,150km2inKonnevesi–
monogynystrategyarepooledandtheirexpectedfre-
quencies(inparentheses)werecalculatedseparately Laukaaregion.
fromthespecies-levelfrequencies. Theforestsweremainly dominatedby Nor-
way spruce (Picea abies (L.) H. Karst.) mixed
P/M Lake Mainland with Scots pine (Pinus sylvestris Linnaeus) and
islands forestplots birches(BetulapubescensEhrh.andB.pendula
Roth) both on the mainland and on the islands.
F.aquilonia P 5(20.2) 61(45.8)
The forests were mostly similar between the
F.lugubris M 16(6.1) 4(13.9)
F.polyctena P 3(6.1) 17(13.9) mainlandandislands,butsomeoftheislandfo-
F.pratensis M 1(0.3) 0(0.7) restsweremoreopenduetorockyhabitats.
F.rufa M 12(4.3) 2(9.7) Inthisstudy,theoccurrence(presentvs.ab-
Polygynous 8(26.3) 78(59.7)
sent) of wood ant assemblages was studied in-
Monogynous 29(10.7) 6(24.3)
steadoftheabundancedataofthenestmounds.
This is because using abundance would cause
some bias to the results since polygynous/poly-
bay,thedistancestothedifferentshorelinesofthe domous species would anyway have multiple
mainland were measured using 90° divergence nests. In addition, a couple of monodomous F.
betweenmeasuredlines,startingfromtheND.In lugubrisnestsonamediumsizeislandmaygive
addition, the area of the islands was measured. higherabundanceperareathane.g.fournestsof
Themeasurementsweremadeusingamapser- F.aquiloniaonalargeisland.
vice (www.retkikartta.fi of Metsähallitus, State All analyses were run using SAS statistical
ForestEnterprise,Finland). softwareversion9.4(SASINC,Cary,IL,USA).
Basedonthemeasuredcontinuousareacov- Generalized linear models (PROC GLIMMIX)
erage of islands, the islands were divided into using binomial distribution (GLM ) and
BINOMIAL
threedifferentsizecategoriesfollowingtheclas- thelogitlinkfunctionwereusedfortheanalyses
sification of Vepsäläinen and Pisarski (1982): oftheprobabilityofoccurrence,andGLMusing
small islands ((cid:1)0.5 ha), medium-sized islands Poisson distribution (GLM ) with the log
(>0.5–<4 ha) and large islands ((cid:2)4 ha). Of the linkfunctionwereusedforthPOeISaSnOaNlysisofspecies
studiedislands,30representedsmallislands,26 richnessofwoodantsontheislands.Alldistance
weremedium-sizedislandsand18werelargeis- measurementswereinter-correlated,whereasis-
lands. land area only correlated with the connectivity
Themainlandforeststandswereasubsample distance(Table2).Duetothishighlevelofinter-
ofthestudyplotsusedinbirdstudiesoftheinsec- correlation,differentsetsofmodelswerecarried
tivorous treecreeper (Certhia familiaris Linnae- out.Connectivitywasalwaysanalysedinsingle
Table2.Pearsoncorrelationmatrixofthedistancevariables(NMD:nearestmainlanddistance,ND:nearestdis-
tancetosuitableterrestrialhabitat,connectivity)andislandarea.
ND Connectivity Islandarea
NMD r=0.263,p=0.02 r=0.295,p=0.01 r=–0.182,p=0.12
ND r=0.787,p<0.0001 r=–0.107,p=0.36
Connectivity r=–0.236,p=0.04
24 Sorvari (cid:127) ENTOMOL.FENNICAVol.29
Table3.Resultsofbinomiallogisticregressionmodelsfortheassociationofbothdistancepredictors(excl.con-
nectivity)andislandareawiththeoccurrenceofdifferentwoodantspeciesonislands.Thestrongestmodelis
evaluatedbyusingeachmodel’sAICvalue(smallerisbetter).ND=nearestdistancetosuitableterrestrialhabi-
tat;NMD=nearestmainlanddistance.Bestmodelsofeachspeciesaresetinbold.
Model AIC Islandarea Secondterm
F.aquilonia area 35.85 F =5.25,p=0.025 –
1,72
area&ND 37.76 F =5.06,p=0.028 F =0.08,p=0.78
1,71 1,71
area&NMD 37.84 F =4.47,p=0.038 F =0.02,p=0.90
1,71 1,71
F.polyctena area 24.90 F =4.78,p=0.032 –
1,72
area&ND 26.52 F =4.54,p=0.037 F =0.22,p=0.64
area&NMD 23.63 F1,71=5.61,p=0.021 F1,71=2.99,p=0.088
1,71 1,71
F.rufa area 63.14 F =6.08,p=0.016 –
1,72
area&ND 64.99 F =6.11,p=0.016 F =0.16,p=0.69
1,71 1,71
area&NMD 64.04 F =4.74,p=0.033 F =0.98,p=0.32
1,71 1,71
F.lugubris area 78.42 F =2.89,p=0.094 –
1,72
area&ND 80.23 F =3.00,p=0.088 F =0.20,p=0.66
1,71 1,71
area&NMD 80.40 F =2.65,p=0.11 F =0.02,p=0.88
1,71 1,71
predictor models. NMD and ND could be ana- 557.3m)hadanyassociationwiththeoccurrence
lysedtogetherwithislandareabutnotwitheach ofdifferentwoodantspecies,buttheprobability
other.Significantpredictorsinthedoublepredic- of occurrence of F. rufa, F. aquilonia and F.
tormodelswerefurtheranalysedinsinglepredic- polyctena increased with increasing island size
tormodelsinbinomialregressionanalysisingen- whileF.lugubrisdidnotshowsuchanassocia-
eralizedlinearmodels. Thestrengthoftheused tion(Table3,Fig.1).Thesinglepredictormodel
doublepredictormodelswerecomparedwiththe forislandareawasstrongerthanthetwopredictor
significant single predictor models using models(islandarea&NMD,islandarea&ND)
Akaike’s information criterion (AIC; smaller is in F. rufa and in F. aquilonia (the AIC value is
better).Inaddition,thestructureoftheislandas- smaller), whereas for F. polyctena island area
semblagesandmainlandforestassemblageswere coupledwithNMDwasastrongermodelthanis-
comparedusinglikelihoodratiotests. land area as a single predictor (with AIC 23.63
and24.90respectively,Table3).
SincetheaspeceisofF.rufawoodantgroup
3.Results
are colony-type polymorphic, the data allowed
thepoolingofthespeciesoverthecolony type.
Of the 74 islands, F. rufa was present on 12 is- The species adapted to the monogyny strategy
lands,F.aquiloniaonfiveislands,F.lugubrison (pooledF.rufa,F.lugubrisandF.pratensis)and
16 islands, F. polyctena on three islands, and F. polygyny(pooledF.aquiloniaandF.polyctena),
pratensisononlyoneisland(Table1).Duetothe and all the wood ants combined increased their
rarityofthespecies,F.pratensiswasnotanalysed probability ofoccurrencewithincreasingisland
in single species models. Twenty-four islands size, whereas such associations were not found
wereinhabitedbywoodantsleavingfiftyislands withNDandNMDinthisarchipelago(Table4,
uninhabited. Fig.2).Inaddition,connectivityhadnosuchas-
Connectivity (mean ± SD: 224.0 m ± 146.6 sociationseither(GLM ,monogyny:F
BINOMIAL 1,72
m)hadnoassociationwiththeoccurrenceofthe =0.14,p=0.71;polygyny:F =0.94,p=0.34;
1,72
woodants(GLM ,F.rufa:F =0.03,p= allcombined:F =0.35,p=0.56).
BINOMIAL 1,72 1,72
0.86;F. aquilonia:F =0.75, p=0.39;F. lu- The number of wood ant species increased
1,72
gubris:F =0.33,p=0.57;F.polyctena:F = withincreasingislandsize(Fig.3),andwhereas
1,72 1,72
0.19,p=0.67).NeitherND(mean±SD:107.8m ND andNMD hadnoassociationswithspecies
± 125.9 m) nor NMD (mean ± SD: 678.2 m ± richness,theislandareahad(Table4).Thestron-
ENTOMOL.FENNICAVol.29 (cid:127) Woodantsonislands 25
Fig.2.Probabilityofoccurrenceincreasedwithanin-
creaseinislandsizeforthefollowingwoodantgroup-
Fig.1.Probabilityofoccurrenceincreasedwithanin- ings.–a.Polygynousspecies(F.aquiloniaandF.
creaseinislandsizeforthreewoodantspecies.–a. polyctena).–b.Monogynousspecies(F.rufa,F.
Formicaaquilonia.–b.F.polyctena.–c.F.rufa.Pre- lugubrisandF.pratensis).–c.Allspeciescombined.
dictedvalues(largecircles)wereobtainedfromabi- Predictedvalues(largecircles)wereobtainedfroma
nomialgeneralizedlinearmodelwith95%confidence binomialgeneralizedlinearmodelwith95%confi-
limits.Smallcirclesrepresenttheobservations. dencelimits.Smallcirclesrepresenttheobservations.
26 Sorvari (cid:127) ENTOMOL.FENNICAVol.29
Table4.Resultsofbinomiallogisticregressionmodelsfortheassociationofdistancepredictors(excl.connectiv-
ity)andislandareawiththeoccurrenceofpolygynousspecies(F.aquiloniaandF.polyctena),monogynousspe-
cies(F.rufa,F.lugubrisandF.pratensis)andallwoodantspeciescombined.Inaddition,theresultsofPoisson
regressionanalysesfortheassociationofthesamesetofpredictorswiththespeciesrichnessofwoodantson
theislandsarepresented.Thestrongestmodelisevaluatedbyusingmodel’sAICvalue(smallerisbetter).ND=
nearestdistancetoasuitableterrestrialhabitat,NMD=nearestmainlanddistance.Bestmodelsaresetinbold.
Model AIC Islandarea Secondterm
Polygyne area 44.20 F =8.97,p=0.0038 –
1,72
area&ND 45.95 F =8.66,p=0.0044 F =0.19,p=0.66
1,71 1,71
area&NMD 45.10 F =9.59,p=0.0028 F =1.14,p=0.29
1,71 1,71
Monogyne area 89.18 F =5.22,p=0.025 –
1,72
area&ND 90.56 F =5.47,p=0.022 F =0.65,p=0.42
1,71 1,71
area&NMD 91.15 F =5.00,p=0.029 F =0.03,p=0.87
1,71 1,71
Woodants area 82.65 F =7.02,p=0.0096 –
1,72
area&ND 84.38 F =7.24,p=0.0089 F =0.28,p=0.60
1,71 1,71
area&NMD 84.64 F =7.16,p=0.0092 F =0.05,p=0.82
1,71 1,71
Speciesrichness area 131.01 F =18.35,p<0.0001 –
1,72
area&ND 132.97 F =18.39,p<0.0001 F =0.05,p=0.83
1,71 1,71
area&NMD 132.95 F =15.29,p=0.0002 F =0.06,p=0.81
1,71 1,71
gest model was with the island area as a single thepresentstudyhighlightthepositiveeffectof
predictor (SmallestAICvalue;Pearsoncorrela- thelargesizeofasuitablehabitatpatchorlarge
tionr=0.405,p=0.0003).Connectivityhadno forestedislands,notonlyforthepolygynousspe-
associationwiththespeciesrichnessofwoodants cies (F. aquilonia, F. polyctena) but also for
inthisarchipelago(GLM ,F =0.66,p= monogynousF.rufa.Thelatterspecieswasfound
POISSON 1,72
0.42). by Dekonink et al. (2010) to favour also large
When the classification of island size was
used,thecoloniesofF.rufa,F.aquiloniaandF.
polyctena occurred mostly on large islands,
whereas the occurrence of the colonies of F.
lugubrispeakedinmedium-sizedislands(Fig.4).
Thelatterresultexplainswhytheprobabilityof
occurrencewasnotsignificantlyassociatedwith
islandsizeforF.lugubris(Table3).
The structure of wood ant assemblages on
Lake Konnevesi islands was dominated by mo-
nogynous species whereas the mainland forest
habitats were more commonly inhabited by the
polygynousspecies(speciesdata:likelihoodra-
tiotest,G2=65.18,p<0.0001;pooleddata:G2=
63.70,p<0.0001;Table1).
4.Discussion
Fig.3.Numberofwoodantspeciesincreasedwithin-
Mabelis (1994) found monogynous species (F.
creaseinislandsize.Predictedvalues(largecircles)
rufa,F.pratensis)morefrequently insmalliso-
wereobtainedfromaPoissonregressiongeneralized
lated forests and polygynous species (F. linearmodelwith95%confidencelimits.Smallcircles
polyctena)inlargeforestpatches.Theresultsof representtheobservations.
ENTOMOL.FENNICAVol.29 (cid:127) Woodantsonislands 27
Fig.4.Proportionalfre-
quencyofspeciesob-
servationsinsmall
(<0.5ha),medium-
sized(0.5–4ha)and
large(>4ha)islands.
Numbersabovebars
representnumbersof
islandsoccupiedby
eachspecies.Mostob-
servationsofFormica
aquilonia,F.polyctena
andF.rufawerefrom
largeislandswhereas
theoccurrencepeaked
forF.lugubrisonme-
dium-sizedislands.Of
thestudiedislands,30
weresmallislands,26
weremedium-sizedis-
landsand18were
largeislands.
pineforests.Ontheotherhand,theoccurrenceof tivespecies-arearelationshipinanarchipelagoin
themostcommonwoodant,F.lugubris,ontheis- theNortheastUSA.Usingarestrictedsetofant
lands did not increase linearly with island size. species,fivewoodantspecies,asimilartrendwas
Themeadowant,F.pratensis,wasonlypresent foundhereasthenumberofwoodantspeciesin-
ononeisland(onenest),andthus,noconclusions creasedwithanincreaseinislandarea.Interest-
about that species could be made based on the ingly, wood ant nests can act as habitat islands
dataofthisstudy. themselves. Päivinen et al. (2004) found an in-
Since none of the distance variables (NMD, creaseinthemyrmecophilousbeetlespeciesrich-
NDorconnectivity)hadsignificantassociations nesswithincreasingvolumeofnestmounds.In
with the occurrence of wood ant species and addition,theprobabilityoftheoccurrenceofthe
wood ant species richness, no evidence of dis- shinyguestant,Formicoxenusnitidulus(Nylan-
tancedecay effectwasfound. Probably thedis- der) (a xenobiont living in wood ant nest
tances weretoo short to causeasignificant dis- mounds), increased with increasing nest mound
persal barrier. However, in the case of polygy- volume (Dietrich 1997, Ölzant 2001, Härkönen
nous F. polyctena, the NMD contributed to the &Sorvari2017).
habitatselectionmodelatsomelevel.Unlikethis Vepsäläinen and Pisarski (1982) studied is-
study, Clark et al. (2011) found significant de- landantpopulationsintheBalticSeaarchipelago
creaseofantspeciesrichnesswithislandisolation close to the Hanko peninsula area in Finland.
inanarchipelagolocatedintheNortheastUSA. They found that most of the wood ant species
Rizalietal.(2010)foundapositivespecies- were only present on large islands but F. aqui-
arearelationshipofantsinanIndonesianarchi- lonia was also found on medium-sized islands.
pelago.SimilarlyClarketal.(2011)foundaposi- Thesamesizeclassificationwasusedhere,andF.
28 Sorvari (cid:127) ENTOMOL.FENNICAVol.29
polyctena was only found on large islands, thus, the colony could survive, but had not
whereasF.rufa,F.aquiloniaandF.lugubriswere enoughresourcestoproducesexualoffspring.In
found on large and medium-sized islands – F. suchsituation,polygynousspeciesmaybecom-
lugubris was even found on small islands. The pletelydependentontheadoptionofnewqueens
frequencypeakedforF.aquilonia,F.rufaandof frommainlandorotherislands.However,mono-
courseF.polyctenaonlargeislands,whereasthe gynousspecies,suchasF.lugubris,maybeable
frequencyofF.lugubrispeakedonmedium-sized to complete the colony cycle and produce new
islands. The ability of F. lugubris to nest on is- sexual generation, due to their ability to live in
lands of all size classes is likely to explain the earliersuccessionalstagesofforests.
commonness of F. lugubris in the Lake Konne- In this study, the monogynous species were
vesiarchipelago. foundmorefrequently thanexpectedonislands
Ants typically colonise new areas in certain andlessfrequentlythanexpectedinthemainland
sequences and first colonisers, the pioneers, are forestplots,whereastheoppositewasfoundfor
oftenreplacedbystrongercompetitorsorspecial- the polygynous species. Thus, the structure of
ists of later successional stages. An example of woodantspeciescommunitieswasfoundtodif-
this from Finnish island habitats is the species ferbetweentheislandpopulationsandthemain-
pairinthegenusLasiuswhereL.niger(Linnae- landforests.Thisisprobablyduetothedifferent
us)isabletocoloniseislandsrapidlybutislargely dispersal and colonisation ability between the
replacedbyitssisterspeciesL.platythoraxSei- monogynousandpolygynousspecies.
fertduringhabitatsuccession(Czechowskietal. Inanearlierwork,Mabelis(1994)suggested
2013).ThewoodantsoftheF.rufagrouparelate that while monogynous F. rufa may have a
successorspecies.Theyaretemporalparasitesof greaterchanceofbecomingextinctthanpolygy-
Formicaspeciesbelongingtoadifferentsubge- nouscoloniesofF.polyctena,itmaybecompen-
nus,Serviformica,suchasF.fuscaandF.lemani. sated for by its higher colonisation rate. In the
Thehostspeciesfoundtheircoloniesindepend- present study, the mainland populations were
entlyandaretypicalspeciesofearlierforestsuc- dominated by the polygynous species, F.
cessionstages.Therefore,colonisationoftheant aquiloniaandF.polyctena,probablybecauseof
speciesoftheF.rufagrouponislandsisalways theirgoodsurvivalovertheyearssincehavinga
dependentonthepresenceofServiformicacolo- high number of queens. They frequently adopt
nies. Another feature in the F. rufa group that new queens and polydomy makes the colonies
makes their colonisation on islands hard is that persistentoverlongperiods.Intheislandpopula-
thespeciesareterritorialanddonottolerateco- tions, polygynous species were found on rela-
specificsandothermembersofthegroupinthe tivelyfewislandscomparedtothemonogynous
vicinity of their nests, thus, possible colonizer ones,probablyduetotheirpoorerdispersaland
queens ofthe species group may be eliminated. colonisation abilities. Abandoned single nests
Thiscertainlyaffectsthecolonisationsuccessof werecommonlyfoundontheislands,whichare
otherwoodantspecies,especiallyinlimitedfo- likelytobetheremnantsofextinctmonogynous
restareasofsmallislands. colonies. The present results seem to support
Punttila (1996) found that F. lugubris is the Mabelis’ suggestion that the higher extinction
most common wood ant species in the young rate of monogynous species is compensated for
successionalstagesofforestsaswellasinsmall bytheirhighercolonisationrates.
old-forestfragments.BasedonPunttila’sresults Inconclusion,itwasfoundthatthestructure
andthepresentstudy,itcanbesuggestedthatthe ofthewoodantcommunityisdifferentonlakeis-
speciesisthemosteffectivecoloniseramongthe landsthanonthemainland.Despitethehighex-
wood ants in Finland and most flexible when it tinction propensity of the monogynous (single
comestohabitatselection. queen) colonies, the monogynous species were
Czechowski and Vepsäläinen (2009) artifi- common on islands, possibly dueto their better
cially introduced a colony of F. polyctena on a colonisationabilitycomparedtothepolygynous
<0.2haislandwherethecolonysurvivedover22 species. In addition, it seems that F. lugubris is
years.Theislandhadonlyveryfewsmalltrees, able to colonise and survive on small islands,
ENTOMOL.FENNICAVol.29 (cid:127) Woodantsonislands 29
which may make it also tolerant to forest frag- tera:Formicidae).—JournalofInsectConservation
mentationinmainlandforests. 21:477–485.
Jäntti,A.,Suorsa,P.,Hakkarainen,H.,Huhta,E.&Kuitu-
nen,A.2007:Withinterritoryabundanceofredwood
Acknowledgements. I am grateful to Jussi Päivinen and
antsFormicarufaisassociatedwiththebodycondi-
HeikkiHellefortheirassistancewithLakeKonnevesiis-
tionofnestlingsintheEurasiantreecreeperCerthiafa-
land populations and Ari Jäntti, Esa Huhta and the late
miliaris.—JournalofAvianBiology38:619–624.
HarriHakkarainenforassistancewithmainlandpopula-
Mabelis,A.1994:Flyingasasurvivalstrategyforwood
tions. In addition, I am grateful to the personnel of the
antsinafragmentedlandscape(Hymenoptera,Formi-
KonnevesiResearchStation(UniversityofJyväskylä)for
cidae).—MemorabiliaZoologica48:147–170.
maintenanceoftheresearchersduringthefieldtrips.Two
MacArthur,R.H.&Wilson,E.O.1967:TheTheoryof
anonymousreviewersgaveconstructivecommentstothe
Island Biogeography. Princeton University Press,
manuscript.TheEnglishlanguagewascheckedbyprofes-
Princeton,NJ,USA.203pp.
sional proof-reader from Lingsoft Company. The study
Morrison,L.W.1997:Theinsularbiogeographyofsmall
wasfundedbyOskarÖflund’sFoundation.
Bahamiancays.—JournalofEcology85:441–454.
Morrison,L.W.2016:Theecologyofants(Hymenoptera:
Formicidae)onislands.—MyrmecologicalNews23:
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