Title

Self organized conflicts in territorial ants

Date of Completion

January 2008

Keywords

Biology, Ecology|Biology, Entomology|Biology, Zoology

Degree

Ph.D.

Abstract

Classic studies of self organization in social insects describe the emergence of behavior for a single group, but few studies have investigated the self organization of conflicts between groups. Territorial disputes in ants provide conveniently studied examples in which dynamics of group conflicts can be traced to individual behavior. A review of territorial battles in ants found that different species exhibit contrasting spatial and temporal patterns. These dynamics arise through a combination of recruitment, mortality, assessment and individual movement patterns. The goal of this research was to determine the role of these processes in shaping territorial conflicts. ^ Lanchester's square law proposes that the fighting ability of a group is proportional to the square of the number of individuals. By analyzing mortality rates during battles of the fire ant Solenopsis invicta Buren, we provide the first quantitative test of this hypothesis for a non-human animal. Replicated experiments rejected Lanchester's square law; instead, group fighting ability rises approximately linearly with group size. ^ I present the first quantitative and experimental study of territorial battles in the invasive ant Tetramorium caespitum Linnaeus. In natural battles and experimentally instigated battles, a dense zone of fighting developed and moved noticeably between the nest entrances of opponents. The movement of the battle zone appears to result from sequential bouts of recruitment by opposing colonies, with newly arriving groups of ants moving through the battle searching for opponents, causing the zone of fighting to move towards the colony with weaker recruitment. Recruitment was achieved by deposition of trail pheromones originating in the poison gland and by individual ants leading groups of nestmates to the site of the conflict. ^ A quantitative model of territorial battles was developed, using differential equations to link changes the numbers of individuals in the battle to recruitment and assessment. This model can generate stable numbers, damped oscillations or stable oscillations in the number of ants present in battle. Time delays in recruitment play a critical role in determining the nature of the battle dynamics, and may be responsible for the spatial oscillations observed in battles of T. caespitum. ^