Combat, co-existence, and resource partitioning in acorn-dwelling Temnothorax ants

Abstract

Coexisting populations of ecologically similar species may reduce competition by decreasing overlap in the resources they use, or by spatially or temporally partitioning shared resources. Temnothorax longispinosus and Temnothorax curvispinosus are morphologically similar acorn-nesting ant species that frequently co-occur in the leaf litter of deciduous forests of eastern North America. By conducting two detailed and complementary field surveys, we show that T. longispinosus and T. curvispinosus nest in a specialized subset of available acorns and that nests had a uniform pattern of spacing consistent with spatial displacement from competition. Colonies of both species were then subjected to laboratory preference tests, and interspecific and intraspecific competition experiments. The preference experiments demonstrated some level of differentiation in resource use among species within the specialized range of nest properties used by the ants in nature, potentially reducing competition during nest selection. Nevertheless, in both intraspecific competition experiments we found high mortality that increased when ants were initially in nests closer together. T. curvispinosus mortality also increased with the number of combatants, consistent with a battle of attrition between opposing sides. In contrast, T. longispinosus mortality decreased during battles as the number of combatants increased. In the interspecific battles, both T. curvispinosus and T. longispinosus sustained some mortality, but escalated battles did not occur. Broadly, this work demonstrates that direct competition over nesting sites is an important mechanism underlying the dispersion of Temnothorax nests and therefore the structuring of acorn-nesting Temnothorax assemblages.