Non-random Size Differences between Sympatric Species of the Ant Genus Leptothorax (Hymenoptera: Formicidae)

Abstract

In temperate and boreal forests, ants of the widely distributed genus Leptothorax may occur in extremely high densities. In most areas, two, occasionally three or more species nest in close proximity. It appears that competition between sympatric species is minimized by morphological differences. Workers from 15 sympatric species pairs differed more strongly in caput width than randomly chosen pairs of allopatric species. Co-occuring species also differed considerably in thorax length. In Leptothorax communities, nest sites rather than food are thought to be the most limited resource. In two pairs of species nesting in preformed cavities in wood, non-random size differences indeed were positively correlated with differences in the average volume of the nest site. Competition for nest sites might therefore influence individual size of Leptothorax species.