TERRITORY SIZE AND SHAPE IN FIRE ANTS - A MODEL-BASED ON NEIGHBORHOODINTERACTIONS

Many aggressive animals form territory mosaics marked by distinct boun daries. This paper describes an approach to modeling territory size an d shape within mosaics based on boundary disputes among neighboring an imals. The model assumes that each resident applies pressure against i ts neighbors, as a result of aggression and display, and that boundari es form curves along which the pressure exerted by adjacent residents is equal. To illustrate, I predicted territory boundaries for populati ons of the fire ant Solenopsis iavicta using several alternative mathe matical descriptions of territorial fighting. According to the most su ccessful formula, the aggressive pressure applied at any point on the territory perimeter increases linearly with the biomass of the defendi ng colony but decreases with territory area and with the square of the distance to the colony's nest. An iterative algorithm predicts the si ze and location of boundary segments given the positions and sizes of colonies. By all measured criteria, this model produced more accurate predictions of territory areas and shapes than alternative models that omit the effects of resident size or the dependence of aggressive pre ssure on territory area. Modifications can incorporate nest relocation s, strategic variation in the degree of aggressive pressure applied, h abitat heterogeneity, and other biological details. However, even with simple assumptions, the model predicts much of the variation in the s izes and shapes of fire ant territories in natural conditions. This im plies that territories are molded by a balance of aggression between n eighbors and that each territory is affected by the actions of numerou s residents.