Lanchester's attrition models and fights among social animals

Lanchester's models of attrition during warfare have servedas the basis for several predictions about conflicts betweengroups of animals. These models and their extensions describerates of mortality during battles as functions of the numberand fighting abilities of individuals in each group, allowinganalysis of the determinants of group strength and of the cumulativenumbers of casualties. We propose modifications to Lanchester'smodels to improve their applicability to social animals. Inparticular, we suggest that the per-capita mortality rate ofa group is a decreasing function of the fighting abilities ofits members, that the mortality rate is an increasing functionof the number of individuals in both groups, and that therewill often be diminishing returns for increasing numerical advantage.Models incorporating these assumptions predict that the abilityof social animals to win fights depends less on group size andmore on individual prowess than under Lanchester's originalmodels. We discuss how data on casualties can be used to distinguishamong alternative attrition models.     

Driver Ants Invading a Termite Nest: Why Do the Most Catholic Predators of All Seldom Take This Abundant Prey?

Driver ants ( i.e. , epigaeic species in the army ant genus Dorylus , subgenus Anomma ) are among the most extreme polyphagous predators, but termites appear to be conspicuously absent from their prey spectrum and attacks by driver ants on termite nests have not yet been described. Here, we report a Dorylus ( Anomma ) rubellus attack on a colony of the fungus-growing termite Macrotermes subhyalinus that was observed during the dry season in a savannah habitat in Nigeria's Gashaka National Park. It was estimated that several hundred thousand termites (probably more than 2.4 kg dry mass) were retrieved. The apparent rarity of driver ant predation on Macrotermes nests may be explained by different habitat requirements, by the fact that these ants mostly forage aboveground, by efficient termite defense behavior and nest architecture that make entry into the nest difficult, and finally by driver ant worker morphology, which differs remarkably from that of subterranean Dorylus species that regularly invade and destroy termite colonies.     

Combat between large derived societies: A subterranean army ant established as a predator of mature leaf-cutting ant colonies

Summary. Mature colonies of Atta leaf-cutting ants are dominant herbivores throughout the Neotropics. Although young colonies have natural enemies, mature colonies, which live in extensive nests containing millions of workers, currently have no recognised predators. New World army ants (Ecitoninae) are specialist social predators of other ants, and the army ant Nomamyrmex esenbeckii, a primarily subterranean species, is known to prey upon young Atta colonies. Here we present the results of the first long-term study of the predator-prey interaction between N. esenbeckii and Atta. Our study establishes the army ant N. esenbeckii as the only known predator capable of successfully attacking and killing mature as well as young colonies of Atta leaf-cutting ants. In natural raids, and experimental tests, Atta rapidly recruited their largest workers (majors) as a specific defensive response to N. esenbeckii raiders and both taxa used their largest individuals in the frontline of battles. The deployment and behaviour of these large workers demonstrates a size-related division of labour and agrees with the predictions of Lanchesters Linear Law of Combat. Both taxa also used cooperative combat teams to overwhelm large combatants from the other side. The success of N. esenbeckii raids varied greatly, such that they were prevented from entering Atta nests in the least successful raids, and completely overran Atta colonies in the most successful raids. The speed and magnitude of the defensive response of mature Atta colonies was key in determining the level of success of N. esenbeckii raids.Received 12 December 2003; revised 25 March 2004; accepted 1 April 2004.Work conducted at the Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Ancon, Republic of Panama     

Do Lanchester's laws of combat describe competition in ants?

Lanchester's laws are mathematical models, originally designedto model military combat, that describe battle outcomes basedon the sizes of armies and the potencies of individual fightingunits. The "square law" describes a scenario in which small-sizedcompetitors may use a numerical advantage to overcome large-sizedcompetitors in simultaneous combat. The "linear law" describeshow a competitor with large-sized fighting units may use one-on-onecombat to favor victory when outnumbered. Lanchester's lawshave been suggested as an important regulator of interspecificcompetition in social insects, but without experimental support. In this study, experimental platforms were designed to invokethe conditions of both Lanchester's laws in a community ofants in lowland tropical wet forest in Costa Rica. I measuredbehavioral dominance at the food platforms in two separatemanners: an ordinal ranking of the number of workers present,and the monopoly of the food platforms. At the platform invokingsimultaneous combat, satisfying the square law, small-sizedants were more behaviorally dominant by numerical superiority.At the platform invoking one-on-one combat, satisfying thelinear law, larger ants were more behaviorally dominant by monopoly. These results suggest that Lanchester's laws explain,in part, the outcome of interspecific competition in ants.