COMMUNITY ECOLOGY 12(1): 9-17, 2011 1585-8553/$20.00 © Akadémiai Kiadó, Budapest DOI: 10.1556/ComEc.12.2011.1.2

Interactions between microcephalum (Formicidae) and other dominant species of sympatric occurrence

L. Petráková1, 2 and J. Schlaghamerský1

Department of Botany and Zoology, Faculty of Science, Masaryk University, Kotláøská 2, 611 37 Brno, Czech Republic

Corresponding author. Fax: +420 532 146 213; e-mail: [email protected]

Keywods: Encounters, Space partitioning, Territorial . Abstract. Interactions of with other two territorial ants also nesting in or foraging on trees, Lasius fuligi- nosus and Formica rufa, were studied in South Moravia (Czech Republic), at the northwestern border of its range, in 2005-2009. L. microcephalum defends its nest and foraging trees. Its distribution area is fragmented and in the north restricted to river floodplains. We investigated whether competition by other behaviourally dominant ant species could limit its distribution. We found six sites where nests of potential competitors were situated close to a L. microcephalum nest tree. We studied the partitioning of space (occupancy of foraging trees) between the species by observation and by lines of pitfall traps placed between nest trees of L. microcephalum and L. fuliginosus. These species avoided each other; the territory border changed over time. Worker interactions, including combats between L. microcephalum and F. rufa colonies, were observed in the field. Aggressive behaviour occurred close to the nest, on trails, foraging trees, and occasionally at food baits. In such situations, L. microcephalum took advantage of worker cooperation. Encounters of single workers were observed in laboratory experiments. L. microcephalum, attacking primarily by biting, lost almost all combats with L. fuliginosus, being paralysed by its secretions. One-on-one encounters with F. rufa led less frequently to combat and chances were more even, but F. rufa prevailed more often. We confirmed the territorial behaviour of L. microcephalum. In the rare situations, in which its colonies occurred together with other territorial species, we observed conflicts but no total displacement of one species by another.

Abbreviation: GEE–Generalized Estimating Equations.

Introduction the trails must be renewed after the winter pause (Quinet et al. 1997). Combats comprise sharp physical aggression (Ma- Conflicts are common in ants as a consequence of niche belis 2003) and spraying chemicals, although they can also overlap and resource competition (e.g., Czechowski 1985, be ritualized as menacing postures without attacks (Höll- 1999, Vepsäläinen and Savolainen 1990). Success depends dobler and Wilson 1990). Competitive interactions can lead on the social organisation of the colony, the workers’ mor- to replacement (Savolainen and Vepsäläinen 1989), perma- phology, the scouts’ ability to localise new resources, the ef- nent conflict (Pereira et al. 2003) or tolerance (Temeles ficiency of recruitment, and the aggressiveness level (Pisar- 1994). Coexistence is possible only if the colonies divide the ski and Vepsäläinen 1989, Holway 1999) as well as physical resources (food, space) complementarily, e.g., food speciali- conditions of a site (Mabelis 1977, Vepsäläinen and Savo- zation, shifts in the use of individual vegetation layers and lainen 1988). Usually, either the strongest competitor or the foraging periods (Bernstein 1975, Hunt 1974, Vepsäläinen one that arrives first takes control over the resource (Höll- and Savolainen 1988). Polydomous systems of colonies fa- dobler and Wilson 1990), whereas the weaker competitors cilitate the exploitation of a foraging area and thus support are pushed back to the less optimal parts of the habitat and colony development. Polydomous ants tend to be also have to use food of lower quality (Sanders and Gordon ecologically dominant (Debout et al. 2007). 2000). This leads to an asymmetric use of space (Pereira et al. 2003). Many myrmecologists suggested a hierarchal order In the present study, we look at the interaction of the within the ant community with varying number of levels dolichoderine ant Liometopum microcephalum (Panzer, (e.g., Vepsäläinen and Pisarski 1982, Schoener 1983). Gen- 1798) with two behaviourally dominant, territorial ant spe- erally, “submissive species” are adaptable and often shift cies with similar requirements. L. microcephalum is a ther- their resource preferences in the presence of a stronger ant mophilous, submediteranean and pontocaspic species. In the species (Savolainen et al. 1989) whereas “territorial species” north of its range the species is restricted to the floodplains at the top are able to defend an area around their nest, trails of large rivers and its distribution area is substantially frag- and monopolized food resources (Levings and Traniello mented; thus the species is considered threatened in many 1981, Hölldobler and Wilson 1990). These species form countries (Makarevich 2003, Bezdìèka 2005, Seifert 2007). huge colonies and often determine the structure of ant com- It reaches its northwestern border of distribution in the Dyje munities (Savolainen et al. 1989, Czechowski and Markó and Morava floodplains in South Moravia (Czech Republic) 2005). Territory borders change dynamically in the course of where its population is large and vital despite its marginal time. Ants fight mostly in the spring when food is scarce and position (Schlaghamerský and Omelková 2007). The ants 10 Petráková and Schlaghamerský build nests several metres above ground in old but living often extending below ground. According to Seifert (2007) it trees, especially oaks. Most foraging takes place on other has a particularly close association with the aphid Stomaphis trees in the vicinity of the nest tree. Several authors (e.g., quercus, which is also tended by L. microcephalum (Wiest Forel 1892, Makarevich 2003) have reported at least some 1967). Workers of similar size (4-6 mm) as those of L. mi- colonies of this species to be polydomous. L. microcephalum crocephalum use effective chemicals (dendrolasin, undecan) is a very efficient hunter (e.g., Zettel et al. 2004, Graben- instead of physical aggression in combat. The species is poly- weger et al. 2005), although aphid tending seems to be also domous. Formica rufa L. 1761 colonies are mostly monodo- an important part of its foraging behaviour (Wiest 1967, Seif- mous (Seifert 2007), building typical ant heaps, most often ert 2007). Workers (3-7 mm) have been reported to be very in coniferous forests (Czechowski et al. 2002). Its workers aggressive towards other ant species (e.g., Forel 1892, Wiest are of bigger size (8–10 mm) than those of the two above- 1967, Grabenweger et al. 2005, Seifert 2007). They attack by mentioned species and very aggressive, using strong mandi- biting and by spraying a secretion which repels enemies, bles as well as chemical weapons (formic acid, decan, unde- marks prey and initiates alarm behaviour (Wilson and Pavan can). 1959, Wiest 1966, Wiest 1967). Andersen (1997) classified We took into account only those sites where the nests of the North American Liometopum species as behaviourally potentially competing species were less than 25 m apart, as- dominant. Most myrmecologists who have observed L. mi- suming that the probability of conflict increased with de- crocephalum would probably consider it a territorial, behav- creasing colony distance. The 25 m threshold was a compro- iourally dominant species (e.g., Wiest 1967, Tartally 2006). mise between the need to find a sufficient number of sites to We posed the question of whether L. microcephalum was study and our assumption that interactions and their effect on indeed a territorial species and if its colonies were able to distribution would be difficult to detect over a longer dis- withstand the competition pressure of sympatric, behaviour- tance. We checked the trees at these sites in autumn, when ally dominant ants. As only a small proportion of L. micro- the activity of workers was markedly lower and the ants cephalum colonies in South Moravia exist outside of the his- moved only close to their nest trees, to tell apart nest trees of toric floodplain (no longer exposed to regular flooding in small colonies and favoured foraging trees (with many work- most parts, due to massive river regulation in the 1970s- ers running up and down the trunk from spring to summer). 1980s), and as we had anecdotal evidence about replacement Six study sites were identified and used within the pre- of its colonies by Formica spp. in dry localities (Josef Chytil, sent study. These sites were situated within three study areas pers. comm.), we assumed that the observed distribution pat- o that covered an oak-dominated floodplain forest (L1; 48 48´ tern might be (amongst other things) the result of competi- o N, 16 49´ E), a moist oak old-growth outside of the flood- tion. The devastating effect of floods on ants nesting at o o plain (R1, R2, R3; 48 44´ N, 16 47´ E), and a large land- ground level had been observed in the very same floodplain scape park with ancient oak trees in moist meadows (P1, P2; (Schlaghamerský 2000). Nests in tree trunks well above the o o 48 48´ N, 16 48´ E). No suitable site was found in the area’s ground level should give L. microcephalum a competitive ad- xerothermic forests. We observed several workers of For- vantage over ants with ground nests in active floodplains, mica polyctena Förster 1850 (a species closely related to F. whereas such species might outcompete L. microcephalum rufa) not far from a L. microcephalum colony at such a site, when and where floods do not occur. This might have con- but we were not able to find a Formica nest within a radius tributed to the fragmented distribution of the species and of 100 m. At all study sites Lasius fuliginosus was the poten- could also lead to a further decline of its population in South tial competitor, but only at one site (R3) was Formica rufa Moravia and elsewhere, as dominant ant species with a less present as well. Table 1 shows the distances between nests of arboricolous way of life might get established in the historic potentially competing colonies. We were not able to find a floodplains. To get a better understanding of the interactions site with neighbouring L. microcephalum and F. rufa colo- of L. microcephalum and its potential competitors, we studied nies without L. fuliginosus in their vicinity. The distribution the space partitioning between their colonies and its changes and abundance of ant species was studied by means of lines over time as well as behaviour during direct encounters. of pitfall traps. Interactions between potentially competing species were assessed using food baits, field observations Materials and methods and observations of one-on-one combats of workers in the laboratory. The study was conducted in South Moravia (south-east- ern Czech Republic) in 2005-2009. We searched for sites Spatial distribution of species where L. microcephalum nests were located close to colonies of other dominant species. In South Moravia, L. micro- Only three sites were suitable for pitfall trapping: L1 was cephalum meets two territorial ant species, both having simi- studied from May to July 2005 and R1 and R2 from May to lar trophic requirements as L. microcephalum (predation and September 2007 (at the latter two the same colony of L. aphid tending) and, in contrast to L. microcephalum, both fuliginosus but two different colonies of L. microcephalum abundant throughout most of the Palearctic (Seifert 2007). were involved). The other sites were located near frequented Lasius fuliginosus (Latreille 1798) also prefers trunks of old pathways or in a castle park, where the risk of the traps being trees, including oaks, but its nests are close to the ground, damaged or lost was high. In all cases the traps were arranged Interactions between ants 11

Table 1. Distances (m) between nests of potentially competing the relationship was different for both species. Actual dis- colonies of L. microcephalum and other behaviourally dominant tances of individual traps were used for the GEE modelling. species at all study sites; underlined distances correspond with Further, we tested for each line of pitfall traps if workers of transects studied by pitfall trapping, first number in brackets the two species occured randomly in the traps or if individual equals the number of trap lines perpendicular to the transect, second number in brackets equals the number of traps in each traps had captured preferentially either one or the other spe- line; two numbers for distances separated by a semicolon indi- cies, which would point at mutual avoidance (Wilcoxon cate that there were two nests of the given species. Paired Test). Additionally, we assessed the differences in numbers of other ant species among the lines of traps (Kruskal-Wallis Test).

Field observations

We tried to evoke conflicts between colonies by placing food baits (tuna with honey or canned meat for cats) between nests or trails of potentially competing species. These baiting in lines perpendicular to a transect between nest trees of po- experiments (n = 25) were conducted at all three study areas tentially competing species (L. microcephalum and L. fuligi- during spring and summer 2007 and 2008 and in spring 2009. nosus) to form a grid, which would cover the space with the The baits were placed in the field between 10.30 and 14.00 highest probability of encounters between the members of and exposed for two hours. We placed always five or ten both colonies. The number of lines was adapted to the dis- baits in equal intervals along a transect between nests (dis- tance between nest trees; standard intervals between lines tances between baits were chosen depending on the transect and between traps were preserved within each site (Fig.1). length). The individual baits were randomly shifted up to one For easier orientation the lines were assigned letters in alpha- metre to the right or left from the transects. Control baits were betical order (A, B, C, etc.), line A being closest to the L. placed in a distance of one metre from the nest or directly on microcephalum nest tree. Small plastic cups (film canisters; the nest tree (ant heap in case of F. rufa). When we found diameter 3.2 cm, depth 4.5 cm) with ethylene glycol as kill- trails of both species leading close to each other, we placed ing and preserving agent served as pitfall traps. The catch one bait between them. was retrieved every two weeks and the cups were exchanged for new ones with new preservative on this occasion. In addition to the baiting experiments, we mapped the Trapped ants were identified to species (according to Seifert position of trunk trails connecting nests with stable food re- 2007 and Czechowski et al. 2002) and counted. For the pur- sources and monitored changes in space and resource parti- pose of data analysis we pooled data of three subsequent trap- tioning in the course of an annual activity period and between ping periods, obtaining three six-week periods for which sta- those of subsequent years. Each site was visited at least two tistical tests were performed separately. The distribution of times per year (spring and summer; 2007-2009). We ob- the datasets did not fulfill the conditions of normality. To served the behaviour of the workers in the area between nests model the relationship between the abundance of both ant for at least 30 minutes during each visit at a given site, i.e., species and the distance from their competitor’s nest tree we how far from their nest towards the rival’s nest the workers used Generalized Estimating Equations (GEE). This regres- moved and if the species encountered (L1 - 14 visits, R - 24 sion method allows implementation of an association struc- visits,P-11visits).Wealsoexperimentally transferred sin- ture that models spatial correlation between captures of both gle workers of the rival species onto the trunks of nest trees species (Hardin and Hilbe 2003). We used unstructured as- of L. microcephalum and L. fuliginosus (surface of ant hill in sociation structure and GEE with Poisson error structure as case of F. rufa) to observe the reaction of the domestic ant the abundances were counts. For each site and date an AN- colony (R1, R2, R3; summer 2007 and 2008, ten replicates COVA type of model was fitted in order to reveal whether for each species in total).

Figure 1. The arrangement of pit- fall traps (1-9= traps, A-E = lines of traps; intervals between traps in each line = 1 m, intervals between lines = 2-2.5 m). 12 Petráková and Schlaghamerský

Aggressiveness tests Table 2. Percentage representation of ant species captured dur- ing the whole trapping season along the three transects studied One-on-one encounters were observed in closed Petri by pitfall trapping (total number of individuals captured at L1: dishes. The ants were collected at the sites L1 and R1-3 and n = 1695, R1: n = 6522, R2: n = 2118). the experiments were carried out on the same day or the day after the ant collection. For each of the two species pairs (L. microcephalum versus L. fuliginosus, L. microcephalum ver- sus F. rufa) 50 runs were observed. The observation ended when one of the rivals was killed or after one hour in the case of no aggression. We never used the same worker for more than one experiment. After each run the dish was wiped out with 70% ethanol to remove smells. We took notes on the behaviour of both ants, in particular, if they started to fight, which species initiated the fight, what tactics they used, and what was the outcome. The encounters were observed by the first author and partially also recorded with a video camera. We used McNemar’s Test to evaluate equal probability of wins (i.e., if forces of both species were balanced). both species were active all over the area for most of the sea- son, but finally L. fuliginosus occupied a larger portion (Fig. Results 3d). The occurrence of both species differed across traps (Wilcoxon Paired Test: P < 0.05) for each line except the Spatial distribution of species middle line C at R1 (all periods) and line A at R2 (first period, In total, 13 ant species were found at the study sites (Ta- when a trail of L. fuliginosus led close to the L. micro- ble 2). Regarding non-dominant species, numbers of indi- cephalum nest tree ). Numbers of ants in traps of a given line viduals did not differ significantly among the trap lines. At varied a lot and highest numbers were found in traps that L1, the catch of the first trapping period in May 2005 showed were placed close to trees or shrubs (visited by foraging that L. fuliginosus workers were penetrating into the area ants). L. microcephalum workers were most active in June close to the L. microcephalum nest tree, reaching line B (Fig. and July. After that their activity decreased gradually. The abundance of ants of both species increased exponentially 2a). After that, the whole area was fully controlled by L. mi- 2 crocephalum (Fig. 2b) till the end of the trapping season. For with the distance from the tree of the competitor (GEE, X 1 that reason we did not test the significance of distribution > 7.81, P < 0.01), but for most study periods the increase was data for this two species obtained at L1. Subsequent research significantly different for the two species (Fig. 4). At R1 the increase of L. microcephalum was significantly steeper than at other sites (R1, R2) in 2007 showed quite different results. 2 At R1 both species were abundant in traps all over the area that of L. fuliginosus in the first two periods (GEE, X 1 >7.3, mainly in spring (Fig. 3a). Later each species dominated the P < 0.001). In the last period the increase of L. fuliginosus was significantly steeper than that of L. microcephalum lines close to its nest tree (Fig. 3b-c). At the second site (R2) 2 (GEE, X 1 = 16.4, P < 0.0001). In this time period, L. micro-

Figure 2. Spatial distribution of workers between nest trees in site L1 in 2005. (black columns = Liometopum microcephalum, grey columns = Lasius fuliginosus, white square = empty trap, missing square = lost trap; line A = closest to L. microcephalum nest, line D = closest to L. fuliginosus nest). Interactions between ants 13

Figure 3. Spatial distribution of workers between nest trees at the sites R1 (a-c) and R2 (d) in 2007 (black columns = Liometopum microcephalum, grey columns = Lasius fuliginosus, white square = empty trap, missing square = lost trap; line A = closest to L. microcephalum nest, line E or C = closest to L. fuliginosus nest).

Figure 4. Relationships between abundance of L. microcephalum and L. fuliginosus and the dis- tance from the competitor’s nest tree in the three time periods at two study sites (in the first pe- riod, curves of both species at R2 overlap). Fitted models were ob- tained from GEE. 14 Petráková and Schlaghamerský cephalum was already reducing its activity outside of nest microcephalum worker with its mandibles and ran back with trees (see also numbers of individuals). At R2 the increase it. Only single L. microcephalum workers on the ground were 2 was similar for both species in the first period (GEE, X 1 = attacked. This went on for almost two hours, after which ob- 0.1, P = 0.81); in the second period the increase of L. fuligi- servation had to be interrupted. Checking again one week nosus was significantly steeper than that of L. micro- later, the situation was similar, but there were far fewer F. 2 cephalum (GEE, X 1 = 5.3, P = 0.02), and in the last period rufa workers present. During the same time period the same the increase of L. microcephalum was significantly steeper F. rufa colony also lost one foraging tree (an old oak) to L. 2 than that of L. fuliginosus (GEE, X 1 = 4.7, P = 0.03). Taking fuliginosus. F. rufa workers were not able to climb up either into consideration the numbers of captured ants, a sharp de- of these two oaks for the rest of the season. Space partitioning crease of L. microcephalum towards the competitor’s nest (of foraging trees with resources such as prey and honeydew) tree was observed during periods of high activity, in particu- thus occurred in early spring and stayed rather stable during lar at R1 (Fig. 4). the rest of the ants’ annual activity period. We were not successful in using food baits to evoke a Field observations conflict between colonies, although we tried several modifi- L. microcephalum and L. fuliginosus moved mainly on cations of setting up the baits. The baits were most often oc- trails of dendritic shape, connecting nest trees with foraging cupied by Myrmica rubra or M. ruginodis. L. microcephalum trees or shrubs, whereas F. rufa workers were often present and L. fuliginosus noticed only those baits placed closest to off their trails. Workers of competing species going out of their nest or trail, whereas F. rufa fed even on baits farther their nests to forage tended to avoid the direction of the com- than the middle of the transect. In three of nine cases, where petitor’s nest. Single foraging trees were monopolized either trails of L. microcephalum and L. fuliginosus came close (1-2 by one or the other species. In several cases we observed that m), both species detected the bait. The species that had ar- the “possession” of foraging trees changed over time, in par- rived first always gained control over the bait (in two cases ticular from one year to another. At L1 we noted no conflict this was Liometopum microcephalum, in one case Lasius and both ant species kept the same foraging trees during the fuliginosus); the late-comer retreated after a very short fight whole period of our study. At the sites R1-3 almost all the or exhibition of menacing behaviour. F. rufa and Liome- single trees, as well as saplings and shrubs in the dense un- topum workers never exploited the same bait. derstorey, were occupied by one or the other of the studied Observing ant behaviour at all study sites (independent ant species. The “possession” of foraging trees often changed of the presence of baits), we observed only a few cases of in a subsequent year but remained stable throughout the ant’s direct aggression. Mostly when a Liometopum worker acci- activity season. In the Lednice Castle Park (P1), where dentally met its potential enemy, both of them jumped aside mainly ancient oaks were scattered in grassland, we observed and ran away. We observed single workers of competing spe- the take-over of a foraging tree of L. fuliginosus by L. micro- cies moving in 2-5 cm distance from each other without cephalum. At another site in the same area (P2) we observed showing aggression. However, aggressive defence behav- the opposite outcome (L. fuliginosus displaced L. micro- iour was apparent on Liometopum trails and close to their cephalum). The only open aggression between colonies that nest trees. Here, and particularly on the nest tree trunks, the we were able to observe occurred in April 2009 in R3 and Liometopum workers attacked the intruder (experimentally involved L. microcephalum and F. rufa. The base of an oak transferred to the trunk) immediately, showing a high level trunk, which had been frequented by F. rufa in 2007 and of cooperation. Several workers held the intruder’s legs 2008, was occupied by hundreds of L. microcephalum work- stretched apart, while others bit into its body. Typical alarm ers. Hundreds of F. rufa workers had assembled on the behaviour was observed – other workers ran around the en- ground around the trunk base, with their mandibles open. emy with wide opened mandibles and lifted gaster. Single L. FromtimetotimeaF. rufa worker ran forward, grabbed a L. fuliginosus workers were more easily defeated than F. rufa

Figure 5. Aggressiveness tests – outcomes of one-on-one combats observed in the lab; a) L. microcephalum vs. L. fuliginosus: McNemar’s X = 15.04, df = 1, p-value = 0.0001; b) L. mi- crocephalum vs. F. rufa: McNemar’s X = 4.65, df = 1, p-value = 0.03. Interactions between ants 15

Table 3. Aggressivenes tests - number of cases in which ant pices) and too low humidity levels (Schlaghamerský and workers applied particular tactics against the competitor during Omelková 2007). Better knowledge of the drier habitats oc- one-on-one combats observed in the lab (species abbreviations: cupied by L. microcephalum in some parts of its range would LIM = Liometopum microcephalum, LAF = Lasius fuliginosus, FOR = Formica rufa). help to assess the importance of these factors. The location of nest trees restricted the use of pitfall trap- ping. Pitfall trap data reflect the changes in worker activity during the season (Czechowski et al. 1995, Vepsäläinen et al. 2000) and allow to detect in which places workers of a given species occur on the ground. The absence of L. fuliginosus workers in traps at L1 originally gave us the impression that L. microcephalum was by far the stronger competitor workers, which were even able to walk with immobile L. mi- crocephalum workers clinging to their legs. L. micro- (Petráková and Schlaghamerský 2007). Subsequent observa- cephalum workers were also attacked immediately after the tions imply that it was caused by the distribution of food re- transfer to the nest of the other competitor species. L. fuligi- sources at L1 – the only permanent trail of L. fuliginosus led nosus workers always paralysed L. microcephalum worker, from the nest to a lime tree situated outside the area covered whereas F. rufa aggressively bit into the rival’s body. by the traps. Data from R1 and R2 confirmed that L. micro- cephalum and L. fuliginosus avoided each other. The two Aggressiveness tests species met most often in the middle between their nest trees, where worker numbers of both species were relatively low in Workers usually did not fight immediately when they comparison to the trap lines close to their nest trees. The were put into the arena but mostly after they ran into each modelling of the relationship between worker abundance and other or when one of them fell on the other accidentally. In distance to the competitor’s nest tree also showed avoidance, one-on-one combats, L. fuliginosus as well as F. rufa seemed in particular L. microcephalum did not approach nest of L. to be stronger than L. microcephalum, although a great deal fuliginosus at R1 for most of season. Results from R2 were of experiments resulted in both species affected (Fig. 5). The ambiguous; worker activity between the two nest trees was most frequent tactics of L. microcephalum was biting into lower than in R1 and both species were also active close to legs or antennae (Tab. 3). Usually the Liometopum worker the competitor’s colonies, which were rather close. The ter- held on to its rival’s limb until paralysed by the rival’s chemi- ritory borders changes over time as reported for many species cal weapons. A strong dose of these substances induced body by other authors (e.g., Hölldobler and Wilson 1990, Akino trembling, repeated opening and closing of mandibles, and and Yamaoka 1999). The territory of L. microcephalum con- loss of coordination down to rigidity. L. microcephalum was sists of nest trees, trails and foraging trees (food resources) paralysed more often and quicker by L. fuliginosus than by that are defended together with their closest surroundings. F. rufa. Liometopum workers were able to paralyse F. rufa This strategy is more efficient than the defence of a continu- workers but were not successful in biting off their legs de- ous area covering also land between the trails (Wilson 1975). spite attempts to do so. On the other hand, Liometopum work- This allows submissive ant species to live in the non-de- ers did not paralyse L. fuliginosus workers but bit off their fended patches. Our expectation to find most individuals of legs easily. other (submissive) species in the traps of the transects’ mid- dle lines (“no-man’s land”) was not met. Submissive species Discussion are very adaptable and tend to quickly localise small food items or forage at different times than dominant ants (Fellers Intensive searching in the field yielded only a few suit- 1987, Czechowski and Markó 2005), which enables them to able sites with nests of other behaviourally dominant species coexist with dominant species. close to L. microcephalum colonies, and in xerothermic oak woods we did not succeed at all. Therefore, we could not make We assume that the mutual avoidance of L. micro- direct observations that would confirm our assumption that cephalum and L. fuliginosus is probably caused by species- competitors largely limit the occurrence of L. microcephalum specific odours. Wiest (1967) observed that L. micro- to floodplains (and other water-logged sites). On the other cephalum avoided L. fuliginosus workers, including dead hand, the lack of strong colonies of potential competitors in ones. Mabelis (2003) pointed out that Formica species avoid the vicinity of the few and small L. microcephalum colonies L. fuliginosus as well. The chemical weapons used by L. present in South Moravia’s xerothermic forests might ex- fuliginosus have been reported to be very powerful plain why L. microcephalum was able to become established (Czechowski 1999), which was also confirmed in our experi- at these sites. In the latest of several reported cases of replace- mental one-on-one combats with L. microcephalum. How- ment by Formica spp., an isolated L. microcephalum colony ever, the chemical substances used should have a stronger ef- at a dry site had been replaced by a Formica rufa colony fect in a closed Petri dish than in a real-life situation. The within a few years in the 1990s (Josef Chytil, pers. comm.). most effective weapon of single L. microcephalum workers Other factors potentially responsible for the observed distribu- was their dentate mandibles (see also Grabenweger et al. tion of L. microcephalum in South Moravia are the lack of suit- 2005). However, a crucial component of the species’ strength able nest trees in the area’s xerothermic oak forests (former cop- in combat is cooperation. Ant species of bigger body size 16 Petráková and Schlaghamerský more often use one-on-one tactics, and profit from their body with L. fuliginosus and F. rufa, the two major sympatric ter- size, whereas small-bodied ants prefer collective combat ritorial ants in South Moravia. However, the coordinated ac- (McGlynn 2000). Wiest (1967) reported that the small myr- tion of workers seems to be its strongest weapon. At sites micine Tetramorium caespitum workers were able to kill where its colonies occurred together with the other territorial several L. microcephalum workers in an experiment and its species, we observed conflicts, but no total displacement of colonies were equally abundant inside and outside of L. mi- one species by another over a study period of several years. crocephalum territories. She also published that only night- Such sites were, however, rare and limited to floodplains and active arboricolous ants lived in its territory and that species similar moist habitats. Here L. microcephalum seems able to nesting on the ground formed smaller nests within L. micro- withstand competition by the top dominant ant species. cephalum territories than outside. We have no experimental Acknowledgements. The study was supported by the Min- data on encounters of worker groups, but we observed coor- istry of Education, Youth and Sports of the Czech Republic, dinated action of fighting workers in the field. Our attempts Research Plan No. MSM0021622416. The Czech Ministry to initiate and observe conflicts of colonies at food baits, of the Environment granted access to the Rendezvous Na- however, were not successful, although this method has been tional Nature Monument and allowed us to collect L. micro- widely used in similar experimental studies (e.g., cephalum specimens by its Exception No. 8375/04- Czechowski 1985, Human and Gordon 1996, Gibb and Ho- 620/1377/04. The Master’s thesis of M. Omelková provided chuli 2004). Workers probably paid little attention to our valuable information on the biology and distribution of L. food baits because they were attracted by bigger and more at- microcephalum as a starting point for the present study. We tractive resources (Sanders and Gordon 2000, Czechowski and are particularly grateful to our colleague S. Pekár, who pro- Markó 2005) - most foraging seems to take place in the trees and vided statistical advise and conducted the GEE modelling. M. Barclay (Natural History Museum, London) kindly also includes aphid tending (Wiest 1967, Makarevich 2003, own checked the English. unpublished results). Other explanations might be “route fidel- ity”, which means that the workers hardly leave their trails (Sa- volainen and Vepsäläinen 1989), or that L. microcephalum References workers did not notice immobile prey. These ants react strongly Akino, T. and R. Yamaoka. 1999. Trunk trail network of Lasius to movement because of their excellent visual orientation (Wiest fuliginosus Latreille (: Formicidae): Distribution 1966, Dietrich and Busch 2004). between conspecific neighboring colonies. Entomol. Sci. 2: Space and resource partitioning between ant colonies 341-346. takes place in early spring when the trails leading to food re- Andersen, A. N. 1997. Functional groups and patterns of organiza- tion in North American ant communities: a comparison with sources have to be renewed after the winter pause (e.g., Ak- Australia. J. Biogeogr. 24: 433-460. ino and Yamaoka 1999). This was also the case for our spe- Bernstein, R. A. 1975. Foraging strategies in ants in response to cies. In the years of our study, spring started repeatedly very variable food density. Ecology 56: 213-219. early with a fast and unexpected rise in temperature. There- Bezdìèka, P. 2005. Formicoidea (mravenci). In: Farkaè, J., D. Král fore, we were not always able to observe the initial phase of and M. Škorpík (eds.), Red List of Threatened Species in the worker activity and we observed fights between colonies Czech Republic: Invertebrates. Agency for Nature Conserva- only in spring 2009 at R3. We did not observe any mass kill- tion and Landscape Protection of the Czech Republic (AOPK), ing on that occasion; from the workers’ behaviour we con- Praha. pp. 384-386. clude that their aggression was ritualized (Temeles 1994, Case, T. J. and M. E. Gilpin. 1794. Interference competition and Mercier et al. 1997). Once a species had taken possession of niche theory. Proc. Nat. Acad. Sci. 71: 3073-3077. a foraging tree and successfully defended it for some time, it Czechowski, W. 1985. Competition between Myrmica laevinodis kept this tree for the rest of the season. The studied species Nyl. and Lasius niger (L.) (Hymenoptera, Formicoidea). Ann. often changed their foraging trees (particularly Zool. 39: 153–173. smaller/younger ones) in the course of subsequent years at Czechowski, W. 1999. Lasius fuliginosus (Latr.) on a sandy dune – sites where these resources were abundant (where trees were its living conditions and interference during raids of Formica sanguinea Latr. 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Myrmecologische Nachrichten 6: 39-47. 321-329. Received March 31, 2010 Quinet, Y., J. C. De-Biseau and J. M. Pasteels. 1997. Food recruit- Revised September 8, November 19, 2010 ment as a component of the trunk-trail behaviour of Lasius Accepted December 6, 2010