Defense of food supply by eusocial colonies

Abstract

Overdispersion of colonies exists in many eusocial insects. Overdispersion can be generated by direct attack on colonies or founders, by defense of space, by defense of food resources being harvested, or by exploitative competition. When direct competitive interactions lead to colony overdispersion, territoriality is said to occur. Whereas solitary territory holders typically defend space, most eusocial colonies defend resource patches rather than space per se. Also unlike solitary territory holders, colonies with forager communication can simultaneously defend several spatially separated food patches. A model explores optimal numbers of scouts (discoverers of patches) and recruits (followers) needed to maximize net rate of energy intake by the colony. Territorial costs are added to the model by requiring a higher investment of foragers per unit resource collected. According to the model, optimal colony size and percentage scouts are more sensitive to changes in patch size than in patch density. If patch defense is required for resource control, a decline occurs in optimal percentage of scouts; the decline is greatest for small colonies. Colonies that must defend patches in order to harvest from them suffer a loss in net energy intake; the loss is greatest for small colonies. It is predicted that among eusocial insects, those with territorial defense of resources should preferentially visit large patches and have comparatively large colony sizes and relatively few scouts. Ways of testing these predictions are discussed. © 1987 by the American Society of Zoologists.