Behaviour 2019
Field test of Lanchester Theory on colonies of the Australian meat ant, Iridomyrmex purpureus
Shaolin Han, Mark Elgar. the University of Melbourne, Melbourne, Victoria, Australia

Disputes over resources, including food, mating opportunities, and habitat are typically resolved through a combination of displays that may lead to lethal fights. For social species, these contests may involve numerous individuals, and concepts from Lanchester Theory, originally developed from human warfare, have been applied to predict the outcome of non-human contests. Mostly, these studies utilize laboratory-based assays that may not reflect colony-level decisions. Using a series of novel field experiments with food resources, we evaluate the applicability of the Square Law and the Linear Law in predicting the outcome of contests involving the meat ant, Iridomyrmex purpureus. First, we find no evidence that body size, a widespread proxy of fighting ability, influences the outcome of the worker-level contests. Second, we show that the outcome of colony-level contests over food resources is mainly determined by colony size, consistent with the square law of Lanchester’s Theory. These results help explain why colonies of I. purpureus, throughout the warmer monthsengage in collective displays that apparently function to assess the size of their neighboring colonies.