Interspecific space partitioning during the foraging activity of two syntopic species of Messor harvester ants

Terrestrial organisms can adopt different spatial strategies that range from absolute territoriality to complete spatial overlap. In ants, several theoretical models have been proposed to predict some aspects of territory formation such as the size-shape or the position of boundaries along the foraging areas of neighbouring colonies. In the present study we investigated the space partitioning during the foraging activity of two sympatric species of harvester ants (Messor wasmanni and M. minor). Colonies of the two species showed a strong territoriality with different levels of spatial overlapping in different seasons. Colonies may have reduced the cost of territorial dispute by not insisting on the same areas. Encounters between foragers belonging to interspecific colonies did not increase the probability of workers coming back to previously visited areas during the different seasons. Moreover, the evaluation of microhabitat features of foraging areas visited by the two species showed clear differences. Ecological implications and possible explanations of such space partitioning are discussed.