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

Interactions of Liometopum microcephalum with other two territorial ants also nesting in or foraging on trees, Lasius fuliginosus 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