Resource characteristics and competition affect colony and individual foraging strategies of the wood ant Formica integroides

Abstract.  1. Resource characteristics and competitive pressure can affect an ant colony's foraging strategy. This study examined the ability of the wood ant Formica integroides to respond, at both the colony and individual levels, to changes in competitive pressure for access to terrestrial and arboreal resources.
2. Because foraging behaviours depend on resource characteristics, foraging for different resource types (e.g. terrestrial and arboreal habitats) produces different spatial or territorial arrangements. In this study, terrestrial contests for resources followed an interference-exploitation tradeoff, while arboreal foragers defended entire trees as absolute territories.
3. Competitive pressure for access to arboreal resources was shown to increase with distance from F. integroides nests.
4. In this study, the ability of F. integroides to defend a resource varied with body size. Large foragers were better defenders than small foragers. For groups of foragers, the ability to defend a resource increased with the ratio of large to small foragers.
5. In response to competitive pressure, F. integroides colonies altered the size distribution of arboreal, but not terrestrial, foragers. An increase in competitive pressure was matched by an increase in the number of large foragers allocated to trees. This response to competition affected the relationship between body size and distance from the nest for arboreal foragers.
6. Foraging behaviours for individual arboreal foragers also varied with competitive pressure. As competition increased, large arboreal foragers spent more time in direct contact with the resource rather than standing between resource patches.