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