Niche Differentiation of Ant Species within Territories of the Wood Ant Formica polyctena

Abstract

The question if dominant ant species affect habitat use of other ant species was studied around two mounds of the territorial Formica polyctena. We sampled foraging ants at 10, 30 and 60 m from the mounds in four vertical layers on rocky outcrop interspersed with small vegetation patches and in neighbouring forest. We tested expected interactions among ant species on the basis of a linear competition hierarchy concept consisting of three levels: territorial (top competitors), encounter (aggressive but nonterritorial) and submissive (nonaggressive) species. We focussed on resource partitioning by space (not by food) and shifts in use of vertical layers of the habitat in presence of the territorial species. F polyctena was present everywhere except in the litter. Its numbers decreased with distance from its mound, although its activity was substantially patchy within each distance zone. The encounter species occurred occasionally in places where F. polyctena was scarce. The submissive F. fusca, morphologically similar to the top dominant, did not respond by layer shifts; but its numbers decreased toward the mound of F polyctena. The submissive Myrmica shifted from surface of ground to litter and shrub layers at high densities of the dominant. Small colonies and short foraging distances of the submissive species allow coexistence within the territory in lowdensity patches of F polyctena. Our ant community consists of three functional guilds corresponding to taxonomic and morphological guilds: the larger above-ground Formicinae, the smaller and compacter Formicinae, and the small litter-inhabiting Myrmicinae. Interference competition is stronger and more effective among the Formicinae than among the Myrmicinae or between the subfamilies, but the top dominant affects all ant species of the community. Coexistence between the submissives and the top dominant is facilitated by niche differentiation and behavioural responses in the presence of the top dominant.