Abstract
Competition is a major force organizing ant communities and results in co-occurring species evolving different strategies for foraging and use of space. Territorial species, as top dominants exclude each other, while shaping the local ant communities both qualitatively and quantitatively. In this study we examined how two territorial species, Formica polyctena and Lasius fuliginosus, can coexist in adjacent territories over long periods of time, and whether they affect co-occurring species of ants in different ways. Field observations in the absence and in the presence of baits were carried out around a L. fuliginosus nest complex surrounded by a polydomous F. polyctena colony in S Finland in 2007-2009. Both species controlled their territories, but were affected by changes in the abundance of the other species and the distance from L. fuliginosus' main nest. They did not have the same effect on the sub- ordinate species in the absence of baits, but the abundance of Myrmica spp. recorded at baits was negatively affected by both of the territorial species. The preferences of the different species for the artificial food sources differed: L. fuliginosus and F. polyctena pre- ferred tuna to honey and Myrmica spp. honey to tuna. More individuals of the subordinate species were recorded in the territory of F. polyctena than of L. fuliginosus, although conflicts with this territorial species were also recorded. During the three years of the study almost no overlaps in the territories of the two territorial species were recorded, and there were mostly minor shifts in the boundaries of the territories. Differences between the two territorial species in their use of space and competitive effects ensured their coexistence at this particular site in Finland.
Highlights
Ants are competitive, both intra- and interspecifically
In 2007 in the “nudum” observations, the most abundant ants recorded in the study area were Lasius fuliginosus, Formica polyctena, Myrmica spp. and Formica fusca, with F. polyctena as the most numerous species (Fig. 2; Kruskal-Wallis 2 = 185.62, P < 0.0001, N = 330 for all species)
The reverse was recorded for L. fuliginosus: the number of individuals recorded in plots decreased with distance and with increase in the number of F. polyctena foragers (GLMM distance z = –12.31, P < 0.0001, F. polyctena z = –20.03, P < 0.0001, N = 660)
Summary
The morphological affinity of ants (all species belong to a single family) is accompanied by ecological similarities, which implies considerable niche overlap between species and competition. Close to the boreal zone (e.g. in southern Fennoscandia), competition among ants ought to be strong because the vegetation period is short, average temperatures low and, supposedly, food scarcer than in warmer areas. The myrmecofauna is much poorer there and ecologically less diversified, than in warmer regions (see e.g. Czechowski et al, 2012). Local ant communities in this area are convenient models for research on interspecific competition
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