Oecologia (2003) 134:587–595 DOI 10.1007/s00442-002-1141-z

COMMUNITY ECOLOGY

Jussi Pivinen · Petri Ahlroth · Veijo Kaitala · Janne S. Kotiaho · Jukka Suhonen · Teija Virola Species richness and regional distribution of myrmecophilous beetles

Received: 14 June 2002 / Accepted: 16 November 2002 / Published online: 20 December 2002 Springer-Verlag 2002

Abstract Four major hypotheses have been put forward Keywords Coleoptera · Formicidae · Resource to explain local species richness of commensal or abundance · Resource distribution · Resource size parasitic species. The resource distribution hypothesis predicts that regionally widespread host species are able to support higher local species richness of commensals or Introduction parasites. On the other hand, the resource size hypothesis predicts that larger hosts can support more species than Four hypotheses have been proposed to explain the smaller hosts, and comparably, the resource abundance patterns of species richness of herbivores: (1) the resource hypothesis predicts that hosts that offer more resources distribution hypothesis, (2) the resource size hypothesis, are able to support more species. Finally, the resource (3) the resource abundance hypothesis, and (4) the concentration hypothesis predicts that hosts that occur in resource concentration hypothesis (Marques et al. 2000, high-density patches support higher species richness. In Christman and Culver 2001). According to the resource this study, we tested the first three of the above distribution hypothesis, regionally widespread plant spe- hypotheses with myrmecophilous beetles and their host cies are able to support richer local fauna of herbivores ants. In addition to species richness of myrmecophilous (Ricklefs 1987; Cornell and Lawton 1992). The resource beetles, we also applied the above hypotheses to explain size hypothesis predicts that larger plants may support the distribution of the beetles. Our data are exclusively more herbivore species than smaller host plants because based on an extensive literature survey. Myrmecophilous large plants are more likely to be found by the herbivores beetles live in naturally fragmented environments com- (Lawton 1983; Brndle and Brandl 2001; Sanches and posed of host ant colonies and they are exclusively Parmenter 2002). The resource abundance hypothesis dependent on ants. We found that the distribution of the predicts that plants that offer more resources are able to host ants and the colony size of the host ants had a support more species of herbivores than plants that offer positive effect on both the species richness and the limited resources (Hunter and Wilmer 1989; Hunter 1992; distribution of myrmecophilous beetles. In the same way, Marques et al. 2000). Finally, the resource concentration we found that myrmecophilous beetle species that are hypothesis predicts that plant species that occur in high- generalists, i.e. have more than one host ant species, and density patches are able to support high species richness thus have more abundant resources, were more widely of herbivores for two reasons: because such patches are distributed than specialist species. Thus, we found support most likely to be found by herbivores and because for the hypothesis that resource distribution, resource size specialist herbivores tend to stay longer in these patches and resource abundance have an effect on species richness (Lewis and Waloff 1964; Root 1973; Goncalves-Alvim and on the distribution of species. and Fernandes 2001). Distribution of species is primarily determined by the J. Pivinen ()) · V. Kaitala · J. S. Kotiaho · J. Suhonen · T. Virola presence or absence of suitable habitats (Ricklefs and Department of Biological and Environmental Science, Miller 2000). Factors that contribute in forming the University of Jyvskyl, suitable habitats are, for example, climate, topography or P.O. Box 35, 40014 Jyvskyl, Finland soil quality. Barriers preventing long-distance dispersal e-mail: [email protected] may also impose distributional limits. However, the most Fax: +358-14-2602321 important limiting factor of the distribution of species has P. Ahlroth been suggested to be the distribution of resources (Quinn Section of Natural History, et al. 1997; 1998). This suggests that generalist species, Jyvskyl University Museum, which are able to use diverse resources, should be more P.O. Box 35, 40014 Jyvskyl, Finland 588 widely distributed than species that are specialising on a Materials and methods single resource. Based on the hypotheses outlined above, it seems that The data set different aspects of resource availability play a pivotal Data in this study are based on an extensive literature survey role in predicting both the species richness and the (Pivinen et al.2002). We extracted data on those beetle species that distribution of species. Most of the hypotheses have been are classified as myrmecophilous according to Koch (1989a, 1989b, derived having a plant–herbivore system in mind. How- 1992) and occur in Denmark, Sweden or Finland (Silfverberg 1992; ever, just as a resource for a herbivore is a plant, a Lundberg and Gustafsson 1995; Hansen 1996). In addition, we included one Nordic endemic beetle species (Eocatops lapponicus resource can be decaying wood for a saproxylic insect Szymczakowski), which is classified as myrmecophilous according (Sverdrup-Thygeson and Midtgaard 1998; Komonen et al. to Szymczakowski (1975). In total, our data consist of 73 2000), cattle dung for a dung beetle (Roslin and Koivunen myrmecophilous beetle species and 34 host ant species (Tables 1, 2001), a host species for a parasite (Morand and Guegan 2). We consider the data based on literature reliable because for 2000) or a host ant for a myrmecophilous beetle (Pivinen most myrmecophilous beetle species and their host ant species there were several observations from independent sources [(for more et al. 2002). detailed information about the data collection see Pivinen et al. Myrmecophilous beetles live in naturally fragmented (2002)]. small patches, ant colonies, and they are dependent on From this study we were forced to exclude nine myrme- ants or habitats created by the ants (Hlldobler and cophilous beetle species. This is because some of their host ant species were identified only to a genus level (see Table 1). We Wilson 1990). In a field study, Pivinen et al. (unpub- classified the myrmecophilous beetle species as specialist or lished data) tested the resource concentration hypothesis generalist depending on whether they had one or more than one (Marques et al. 2000) with ants and myrmecophilous host ant species. In Denmark and Sweden there were nine and in beetles, and found that ant nests that occur in higher Finland four specialist beetle species. densities are more likely to be found by myrmecophilous beetles. To our knowledge, the other three of the above Species richness of myrmecophilous beetles hypotheses have not been directly tested with any other animal group but herbivores. We used the number of myrmecophilous beetle species observed It is possible that ant colonies differ in their suscep- with each ant species as a measure of the species richness. To analyse the effect of the number of queens in ant colony on the tibility to invading myrmecophilous beetles. One factor species richness of myrmecophilous beetles, we divided the host that could affect the susceptibility is related to how many ant species into monogynous (single queen in each colony) and queens there are in the ant colony. This is because polygynous (several queens in each colony) species (Collingwood workers of monogyne (single queen) ant colonies are able 1979; Czechowski 1990; Hlldobler and Wilson 1990). If host ant species had both monogynous and polygynous populations, we to discriminate between nest-mated queens, i.e. queens considered the host ant species to be polygynous. To analyse the which have mated in the nest in which the queen was effect of colony size on the species richness of myrmecophilous born, and queens that have mated outside their home-nest beetles, we divided the colony size of the host ant into four classes (Sundstrm 1997). In contrast, workers of polygyne according to the number of workers (class 1 = under 1,000 workers per colony, class 2 =1,000–10,000 workers per colony, class 3 (multiple queens) ant colonies are characterised by a =10,000–100, 000 workers per colony, class 4 = over 100,000 low degree of discrimination between nest-mated and workers per colony) (Brian 1950; Breen 1979; Collingwood 1979; non-nest-mated queens. As a consequence, it is possible Savolainen and Vepslinen 1988; Czechowski 1990; Hlldobler that polygynic ant species are generally more indiscrim- and Wilson 1990). inant and behave more tolerantly also towards myrme- cophilous beetle species. Thus, we hypothesise that the Distribution of myrmecophilous beetle species species richness of myrmecophilous beetles may differ between polygynous and monogynous ant species. The distribution of species can be divided into three classes In this study, we analyse the patterns of species according to spatial scale: local, regional and continental distribu- tion (Hughes 2000). We describe the regional distribution of host richness and the distribution of myrmecophilous beetle ants by the number of provinces that the species occupy (Colling- species. We used data of myrmecophilous beetles and wood 1979). In total there are 11 provinces in Denmark, 31 in their host ants in northern Europe (Denmark, Sweden and Sweden and 20 in Finland. The size of the provinces in Finland, Finland) drawn from literature (see the review by Sweden and Denmark is relatively similar (see the map in Collingwood1979). When we use “a beetle species’ host ant’s Pivinen et al. 2002). Because myrmecophilous beetles distribution” we mean the total distribution of all of the host ant are dependent on ants (Hlldobler and Wilson 1990), we species. This was calculated as the number of provinces that were define the host ant species as a resource for each occupied by at least one of the host ant species. Correspondingly, in myrmecophilous beetle species. We test whether resource Sweden and Denmark we described the distribution of the beetles distribution, resource size or resource abundance hypoth- by the number of provinces that the species occupy (Lundberg and Gustafsson 1995; Hansen 1996). In Finland the provincial distri- esis explain the species richness and distribution of butions of the beetle species are missing. Therefore, to describe the myrmecophilous beetles. In addition, we test if species distribution of beetle species in Finland, we used the number of richness of myrmecophilous beetles is affected by the occupied 10-km grid square ranges. There are 3,900 such grid number of queens (monogyny/polygyny) the host ant squares within the land area of Finland. Rassi (1993) has divided them into 12 categories. For example, if a beetle species belongs to species has. category 1, it has been observed in 3,201–3,900 grid squares in Finland. We used the minimum number of grid squares (in this example 3,201) to describe the distribution of a beetle species. The 589 Table 1 Myrmecophilous beetle species and their host ant species. Abbreviations in the column “host ant” are explained in the Table 2 Ant associated beetle species Host ant Ptiliidae Ptenidium formicetorum Kraatz Lbrun, Lfuli, Frufa, Fpoly, Faqui, Fprat Ptilium myrmecophilum Allibert Lasius spp., Fsang, Frufa, Fprat, Ftrun, Faqui Cholevidae Eocatops lapponicus Szymczakowski Flema Scydmaenidae Euconnus claviger Mueller and Kunze Lnige, Lfuli, Lbrun, Frufa, Faqui Euconnus maklinii Mannerheim Lnige, Lbrun, Lfuli, Frufa Euconnus pragensis Machulka Clign, Lnige, Lbrun, Frufa Euthiconus conicicollis Fair. and Lab. Lnige, Lbrun, Lfuli, Frufa Microscydmus minimus Chaudoir Lnige, Frufa Microscydmus nanus Schaum Lasius spp., Frufa, Fprat Scydmaenus hellwigii Herbst Lbrun, Lfuli, Frufa, Fpoly Scydmaenus perrisii Reitter Lbrun Scydmoraphes minutus Chaudoir Cherc, Lbrun, Lnige, Lfuli, Frufa, Fprat Stenichnus godarti Latreille Lbrun, Lfuli, Lnige, Frufa Staphylinidae Amarochara bonnairei Fauvel Lbrun, Lfuli Atheta confusa Mrkel Lfuli, Frufa Atheta flavipes Gravenhorst Lflav, Fexse, Fsang, Frufa, Fprat, Fpoly, Faqui, Ftrun, Flugu Atheta talpa Heer Lfuli, Frufa, Fprat, Fpoly, Faqui, Ftrun, Fexse, Flugu Dinarda dentata Gravenhorst Ffusc, Fsang, Frufi, Fexse, Fcine, Faqui Dinarda hagensii Wasmann Fexse, Fprat Dinarda maerkelii Kiesenwetter Frufa, Fprat, Fpoly, Ftrun, Flugu, Fsang Drusilla canaliculata Fabricius Mscab, Mrugi, Mrubr, Msulc, Tcaes, Lacer, Lnige, Lfuli, Lflav, Lbrun, Lalie, Fsang, Ffusc, Fexse, Frufa Euryusa coarctata Mrkel Lbrun Euryusa optabilis Heer Lbrun, Lnige, Lfuli, Frufa Euryusa sinuata Erichson Lbrun, Lfuli Gyrohypnus atratus Heer Lfuli, Frufa, Faquilonia, Fpoly, Fprat Lamprinodes saginatus Gravenhorst Mrugi, Msabu, Mscab, Mrubr, Lflav, Lfuli, Ffusc, Frufa, Fexse, Fsang Leptacinus formicetorum Mrkel Lbrun, Frufa, Fprat, Fexse, Fpoly, Faqui, Fural, Frufi Lomechusa emarginata Paykull Mrubr, Mrugi, Msabu, Msulc, Mrugu, Mscab, Lasius spp., Ffusc, Frufa, Fsang Lomechusa paradoxa Gravenhorst Mrubr, Mrugi, Mscab, Mrugu, Ffusc, Frufi, Fcuni, Swest Lomechusa pubicollis Brisout de B. Mrubr, Msulc, Mrugi, Tcaes, Lfuli, Lnige, Lalie, Lflav, Lumbr, Ftrun, Ffusc, Frufa, Frufi Lomechusoides strumosus Fabricius Fsang, Frufa, Fprat Lyprocorrhe anceps Erichson Lfuli, Fexse, Frufa, Fprat, Faqui, Ftrun, Flugu, Fnigr Oxypoda formiceticola Mrkel Lasius spp., Ffusc, Fpoly, Fexse, Frufa, Faqui, Flugu Oxypoda haemorrhoa Mannerheim Lfuli, Fpoly, Faqui, Fexse, Fsuec, Fsang, Frufa, Fprat, Ftrun, Flugu, Fnigr Oxypoda pratensicola Lohse Fexse, Fprat, Fnigr Oxypoda rugicollis Kraatz Lasius spp., Fexse, Frufa, Fprat Oxypoda vittata Mrkel Lfuli, Frufa Quedius brevis Erichson Lfuli, Fsang, Frufa, Fexse, Faqui, Flugu Stenus aterrimus Erichson Frufa, Fprat, Fnigr Thiasophila angulata Erichson Lfuli, Lbrun, Frufa, Fprat, Faqui, Fpoly, Fsang, Fural, Flugu Thiasophila bercionis Bernhauer Fural, Fexse Thiasophila canaliculata Mulsant and Rey Frufa, Fexse Thiasophila inquilina Mrkel Lfuli, Frufa, Fprat Thiasophila lohsei Zerche Fprat Thiasophila wockii Schneider Cvagu, Cherc Zyras cognatus Mrkel Lbrun, Lnige, Lfuli, Ffusc, Fexse Zyras funestus Gravenhorst Lfuli Zyras humeralis Gravenhorst Lbrun, Lumbr, Lfuli, Frufa, Fprat, Faqui Zyras laticollis Mrkel Lfuli Zyras limbatus Paykull Mrubr, Mscab, Lfuli, Lflav, Lbrun, Lnige, Ffusc, Fsang, Fexse Zyras lugens Gravenhorst Lbrun, Lfuli Pselaphidae Batrisodes adnexus Hampe Myrmica spp., Camponotus spp., Lbrun Batrisodes delaporti Aub Lbrun, Lfuli Batrisodes hubenthali Reitter Lbrun, Lnige Batrisodes venustus Reichhenbach Mscab, Clign, Lbrun, Lfuli, Lnige, Frufa, Ffusc Chennium bituberculatum Latreille Tcaes Claviger longicornis Mller Lumbr, Lnige, Lfuli, Lbrun, Lflav, Lmixt Claviger testaceus Preyssler Mrubr, Mscab, Tcaes, Lbrun, Lumbr, Lmixt, Lalie, Lfuli, Lnige, Lflav 590 Table 1 (continued) Ant associated beetle species Host ant Histeridae Abraeus parvulus Aub Lasius spp. Aeletes atomarius Aub Lnige, Formica spp. Dendrophilus pygmaeus Linnaeus Lfuli, Fpoly, Frufa, Fprat, Fexse, Fpoly, Faqui Hetaerius ferrugineus Olivier Mscab, Lacer, Terra, Lfuli, Lnige, Lflav, Ffusc, Fprat, Frufi, Fsang, Frufa, Fcine, Fexse Myrmetes paykulli Kanaar Lasius spp., Frufa, Fprat, Fpoly, Faqui Scarabaeidae Potosia cuprea Fabricius Frufa, Fprat, Fural Nitidulidae Amphotis marginata Fabricius Lfuli Monotomidae Monotoma angusticollis Gyllenhal Frufa, Fpoly, Fprat, Flugu, Faqui Monotoma conicicollis Aube Frufa, Fpoly, Faqui, Fprat, Fural, Flugu Cryptophagidae Spavius glaber Gyllenhal Frufa, Fpoly, Faqui, Fural Bothrideridae Oxylaemus variolosus Dufour Lfuli Latridiidae Corticaria inconspicua Wollaston Frufa, Fprat Corticaria longicollis Zetterstedt Lnige, Frufa, Fprat, Fpoly, Faqui Tenebrionidae Myrmechixenus subterraneus Chevrolat Lnige, Lfuli, Fexse, Ffusc, Frufa, Fprat, Fpoly, Faqui Chrysomelidae Clytra quadripunctata Linnaeus Ffusc, Fexse, Frufa, Fprat, Fsang, Faqui, Flugu only exception is when a beetle species belongs to category 12, Results which means that a species has been observed in 0–3 grid squares in Finland. In these cases, we used number 1 rather than number 0. When we analysed the distribution of beetle species, we pooled the Species richness of myrmecophilous beetles data from Denmark and Sweden. We analysed how myrmecophilous beetle species distribution Host ant species that had the widest distribution in follows the distribution of its host ant northwards. This analysis was Denmark, Finland and Sweden supported the highest carried out only with data from Sweden because the latitudinal gradient in Denmark is weak and the provincial distributions of the species richness of myrmecophilous beetles (Spearman’s beetle species are missing in Finland. We measured the distance rs=0.43, n=34, P=0.012; Fig. 1). When we analysed the from the southernmost point of Sweden to the northernmost effect of colony size of the host ants and the number of observation of the beetles and their hosts. The northernmost host ant queens on the species richness of the myrme- observations are based on the provincial distributions such that the cophilous species, we found no significant interaction northernmost observation is the southernmost point of the province (Collingwood 1979; Lundberg and Gustafsson 1995). (two-way ANOVA, F1, 20=0.94, P=0.345). However, we found a significant positive main effect of colony size of the host ant on species richness of the myrmecophilous Statistical analysis beetles (two-way ANOVA, F3, 20=8.82, P=0.001; Fig. 2). In many cases our data were not normally distributed and we used The number of the queens had no effect on the species nonparametric statistics. In a few cases our data met the parametric richness of myrmecophilous beetles (two-way ANOVA, assumptions and in some cases we were able to transform the data F1, 20=0.01, P=0.917). (log-transformation) to meet the assumptions. In these cases parametric statistics were used. When explaining the distribution of myrmecophilous beetles we tried to use multivariate statistics. However, due to a strong correlation between the independent Distribution of myrmecophilous beetle species variables (correlation between the number of host ant species and the distribution of host ant species; Denmark and Sweden: There was a strong positive relationship between the Spearman’s rs=0.86, n=64, P<0.001; Finland: Spearman’s distribution of the host ant species and the distribution of rs=0.70, n=64, P<0.001), there existed a multicolinearity problem in the data. Multicolinearity causes the problem that the standard the myrmecophilous beetle species living with it in errors of regression coefficients are inflated and that results on Denmark and Sweden (Spearman’s rs=0.61, n=64, slopes drawn out of multiple regression are likely to be spurious. P<0.001; Fig. 3a) and in Finland (Spearmans rs=0.43, For this reason we used only simple univariate statistics when n=48, P=0.003; Fig. 3b). Despite these strong positive analysing the distribution of myrmecophilous beetles. relationships, the distribution of myrmecophilous beetles 591

Fig. 1 Species richness of myrmecophilous beetle species in Fig. 2 Species richness of myrmecophilous beetle species in relation to the distribution of their host ant species (number of relation to the colony size (number of workers) of their host ant provinces) in Denmark, Finland and Sweden. Each dot represents in Denmark, Finland and Sweden. Class 1 = less than 1,000 one host ant species; sunflower petals represent the number of workers/colony, class 2 =1,000–10,000 workers/colony, class 3 overlapping data points =10,000–100,000 workers/colony, class 4 = more than 100,000 workers/colony. Error bars represent mean €1 SE

Fig. 3 a Distribution of myrmecophilous beetle species in relation species in relation to the distribution of their host ants in Finland. to the distribution of their host ants in Sweden and Denmark. Each Each dot represents one myrmecophilous beetle species; sunflower dot represents one myrmecophilous beetle species; sunflower petals petals represent the number of overlapping data points. The represent the number of overlapping data points. The distribution of distribution of host ants is the number of provinces and the host ant species and myrmecophilous beetle species are the number distribution of beetles is the number of 10-km grid squares. Note of provinces they occupy. b Distribution of myrmecophilous beetle that Y-axis is in logarithmic scale towards the north was significantly smaller than the direction but the difference was not significant (two- corresponding distribution of their host ants in Sweden sample t-test, t=1.15, df=46, P=0.256; Fig. 6b). (Wilcoxon Signed Ranks Test, Z=5.01, n=64, P<0.001; Fig.4). The number of host ant species each myrme- cophilous beetle species had was positively related to the Discussion distribution of the myrmecophilous beetle species in Denmark and Sweden (Spearman’s rs=0.59, n=64, Species richness and distribution in relation P<0.001; Fig. 5a) and in Finland (Spearman’s rs=0.45, to resource distribution n=48, P=0.001; Fig. 5b). When we categorised myrme- cophilous beetle species as specialists, which have only We found that species richness and distribution of the one host ant species or generalists with several host ant myrmecophilous beetles was positively related to the host species, we found that generalist species were more ant’s distribution. This observation is in line with the widely distributed than specialist species in Denmark and resource distribution hypothesis, according to which the Sweden (two-sample t-test, t=3.35, df=62, P=0.001; distribution of hosts should have a positive effect on the Fig. 6a) and in Finland the tendency was in the same species richness and distribution of the species hosted 592 taxa, local abundances of species often decline from the centre of their geographical range towards the edges (Bock and Ricklefs 1983; Thomas et al. 1999). Therefore, we may expect that ants that are on the edge of their distributional range may have isolated colonies. In a field study with Formica aquilonia Yarrow, Pivinen et al. (unpublished data) found that isolation of the colonies is a good predictor of the occurrence of myrmecophilous beetle species. If this pattern is general, the above observation that edge species support only few host species may be the result of the isolation of the host colonies. We found that the distribution of the myrmecophilous beetle species was positively related to the distribution of their host ants. We also found that distribution of Fig. 4 The northernmost observation (NMO) of myrmecophilous beetle species in relation to the NMO of their host ant species in myrmecophilous beetle species towards the north was Sweden. Each dot represents one myrmecophilous beetle species; less than the distribution of their host ants. These results sunflower petals represent the number of overlapping data points. clearly show that in addition to species richness, the The line represents one to one line. The values in both axes are the resource distribution hypothesis may also be used to distance (km) from the southernmost point of Sweden to the predict the distribution of species. In fact, it is a rather northernmost observation of the beetle (y-axis) or their host ants (x- axis) general finding that the distribution of hosts also has an effect on the distribution of species that are dependent on the host (Koizumi et al. 1999; Webb and Pullin 2000; (Claridge and Wilson 1981; 1982; Neuvonen and Niemel Magagula and Samways 2001). However, an interesting 1981; 1983; Cornell 1985; Quinn et al. 1997, 1998). This question that remains to be answered is why the pattern may be a direct consequence of a species-area distribution of the myrmecophilous beetle species under- relationship hypothesis (MacArthur and Wilson 1967), matches the distribution of their host ants towards the according to which the number of species increases with north? One explanation for the observed undermatching increasing area. may be found if we consider the effect of colony isolation Interestingly, we noted that four of the five ant species on the occurrence of myrmecophilous beetles (Pivinen et (Tapinoma erraticum Latreille, Stenamma westwoodii al., unpublished data); the density of ant populations Westwood, Camponotus vagus Scopoli and Formica decreases towards the north (Baroni Urbani and Colling- cunicularia Latreille), which have been encountered with wood 1977) and isolated colonies rarely support many only one myrmecophilous beetle species (see Table 2), myrmecophilous beetles (Pivinen et al., unpublished are local and live on the edge of their distribution in the data). Thus it seems likely that ant populations in the study area. The fifth one (Formica suecica Adlerz) is north may often be too sparse to allow myrmecophilous endemic to northern Europe (Collingwood 1979). In other beetles to persist.

Fig. 5 a Distribution of myrmecophilous beetle species in relation their host ant species in Finland. Each dot represents one to the number of their host ant species in Sweden and Denmark. myrmecophilous beetle species; sunflower petals represent the Each dot represents one myrmecophilous beetle species; sunflower number of overlapping data points. The distribution of beetle petals represent the number of overlapping data points. Distribu- species is the number of 10-km grid squares. Note that Y-axis is in tions are the number of provinces the species occupy. b Distribu- logarithmic scale tion of myrmecophilous beetle species in relation to the number of 593

Fig. 6 a Distribution of specialist (one host ant species) and b Distribution of specialist (one host ant species) and generalist generalist (several host ant species) myrmecophilous beetle species (several host ant species) myrmecophilous beetle species in in Denmark and Sweden. Distributions are the number of provinces Finland. Distributions are the number of provinces each species each species occupy. Error bars represent means €1 SE. occupy. Error bars represent means €1 SE

Table 2 Host ant species. In the column “Number of queens” 1 = colony, 2=1,000–10,000 workers per colony, 3=10,000–100,000 one queen / nest and 2 = several queens / nest. In the column workers per colony, 4= over 100,000 workers per colony) “Colony size (number of workers)” 1= under 1,000 workers per Host ant species Abbreviation Number of Number Colony size used in Table1 myrmecophilous of queens (number of workers) beetle species Tapinoma erraticum Latreille Terra 121 Myrmica ruginodis Nylander Mrugi 522 Myrmica rubra Linnaeus Mrubr 821 Myrmica rugulosa Nylander Mrugu 221 Myrmica sabuleti Meinert Msabu 221 Myrmica scabrinodis Nylander Mscab 821 Myrmica sulcinodis Nylander Msulc 311 Stenamma westwoodii Westwood Swest 111 Leptothorax acervorum Fabricius Lacer 221 Tetramorium caespitum Linnaeus Tcaes 412 Camponotus herculeanus Linnaeus Cherc 211 Camponotus ligniperda Latreille Clign 223 Camponotus vagus Scopoli Cvagu 121 Lasius alienus Frster Lalie 31 Lasius brunneus Latreille Lbrun 26 2 Lasius flavus Fabricius Lflav 821 Lasius fuliginosus Latreille Lfuli 37 2 4 Lasius mixtus Nylander Lmixt 21 Lasius niger Linnaeus Lnige 21 1 2 Lasius umbratus Nylander Lumbr 41 Formica aquilonia Yarrow Faqui 22 2 4 Formica cinerea Mayr Fcine 22 Formica cunicularia Latreille Fcuni 11 Formica exsecta Nylander Fexse 20 2 1 Formica fusca Linnaeus Ffusc 14 2 1 Formica lugubris Zetterstedt Flugu 11 2 3 Formica polyctena Frster Fpoly 18 2 4 Formica pratensis Retzius Fprat 30 2 4 Formica rufa Linnaeus Frufa 46 2 4 Formica rufibarbis Fabricius Frufi 521 Formica sanguinea Latreille Fsang 14 2 3 Formica suecica Adlerz Fsuec 1 Formica truncorum Fabricius Ftrun 722 Formica uralensis Ruzsky Fural 72 594 Species richness and distribution in relation We found that there was a positive relationship between to resource size and resource abundance the distribution of myrmecophilous beetles and the number of host ants they have. Moreover, we found that The resource size and resource abundance hypotheses are generalist species of myrmecophilous beetles were more very closely related in that large resources could be widely distributed than specialist species. One contribut- considered to offer abundant resources. Thus, we do not ing factor could be differential colonisation success of separate them strictly but rather discuss them more or less generalist and specialist species. If generalist beetle together. The resource size hypothesis predicts that large species are more likely to find another suitable ant plants are more likely to be found and colonised by colony than specialist species, the colonisation success of herbivores both in ecological and evolutionary timescale specialist species may be lower than that of generalist (Neuvonen and Niemel 1981; Lawton 1983; Brndl and species leading to the wider distribution of generalist Brandl 2001; Sanches and Parmenter 2002). Moreover, beetles. species losses through local extinction may be reduced because large plants are able to support larger herbivore populations (Lawton 1983). Similarly, the resource Species richness in relation to number of host queens abundance hypothesis predicts that plants that offer more abundant resources have the potential to support more We hypothesised that species richness of myrmecophilous species of herbivores (Hunter and Wilmer 1989; Hunter beetles could be higher among those host ant species 1992; Marques et al. 2000). which are polygynous (see Sundstrm 1997). However, The above reasoning may be applied to the occurrence there was no difference in the species richness of of myrmecophilous beetle species in ant colonies of myrmecophilous beetles between mono- and polygynous different sizes. We found that there was a positive effect host ant species. However, the numbers of queens vary of colony size on species richness of myrmecophilous between colonies within ant species (Hlldobler and beetles. In other words, resource size or resource abun- Wilson 1990). In our study, we classified the host ant dance had a positive effect on species richness of species as polygynous if it had both mono- and polyg- myrmecophilous beetles. Even though it is not known ynous populations. Our results may have been affected by how myrmecophilous beetle species discover new ant this classification. We propose that in future when colonies when they disperse, it may be that larger and comparing mono- and polygynous host ants, examination non-isolated colonies are found more easily and thus are should be within species rather than across species. With more likely to be colonised by dispersing myrme- our current data such comparison was not possible. cophilous beetles. This view is supported by the finding that myrmecophilous beetles occur only rarely in small and isolated colonies (Pivinen et al., unpublished data). Conclusions Interspecific competition over resources could also play a role in determining species richness of myrmecophilous We conclude that the hypotheses predicting species beetles in ant colonies. Small and isolated ant colonies richness and distribution of plants and herbivores are with limited resources can support only a few species, and also useful when studying other host commensalist or even if colonisation of isolated colonies were successful, parasite systems such as ants and myrmecophilous the number of myrmecophilous species in such colonies beetles. The only requirement is that there needs to be a could be reduced through competitive exclusion. There is clearly definable resource (host) on which the commen- yet another plausible reason for the result that large ant sals or parasites are dependent. Our results from myrme- colonies support more diverse myrmecophilous beetle cophilous beetles clearly support the resource distribution, fauna. Most myrmecophilous beetle species, on which resource size and resource abundance hypothesis. In such knowledge is available, are xerophilous, i.e. they are addition, our results support the hypothesis that generalist dependent on dryness (Koch 1989a, 1989b, 1992). In host species are more widely distributed than specialist ants there exists a rather general positive correlation species. between colony size and nest size (Hlldobler and Wilson 1990). In small nests the environment is not very stable Acknowledgements We are grateful to Jouni Laakso, Satu and rain, for example, has a strong effect on the inside Paukku, Tero Toivanen and Katja Tynkkynen for improving the manuscript. Special thanks to Atte Komonen and Tomas Roslin for humidity of the nest. However, larger nests, such as for their valuable comments. We also thank Pekka Punttila, Michael example Formica nests, are more stable and their inner Saaristo, Jouni Sorvari and Lotta Sundstrm for their comments layer is dry most of the time. This could contribute to the concerning the ecology of ants. The study was financially observed positive relationship between colony size and supported by the Academy of Finland (to V.K. and to J.S.K.), the Entomological Society of Finland (to J.P.), Finnish Centre of species richness of myrmecophilous beetles. Excellence Programme 2000–2005 (V.K. and J.S.; project 44878), Brown (1984) suggested that generalist species will be the Finnish Cultural Foundation / Central Finland (to J.P.), the able to occupy larger geographic ranges because they can Societas pro Fauna et Flora Fennica (to J.P.) and Jenny and Antti tolerate broad environmental spectra. 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