Aggression in social animals: Effects of group size resource holding potential and costs of fighting on the outcome of battles

Animals of the same species often come into conflict with one another over ownership of essential resources, such as food, shelter, territory or mates, which are essential for ensuring their survival and chance to reproduce. These conflicts may occur between pairs of individual animals and result in a 'fight', or they may occur between groups of individual animals and result in a 'battle'. This is likely to happen when groups of social animals, such as humans, apes or social insects come into conflict, usually over the ownership of territory. Many studies have investigated the resolution of fights but far less is known about the factors that determine victory in battles. In fights an individual's fighting ability is the main factor that determines whether it will win. In battles the number of individuals in each group should have a strong effect on which group wins, but the effect of differences in the fighting ability of the individuals that make up each group is not well understood. Also, the way in which individuals engage one another within the battle might influence the contribution that group size and fighting ability make to the chance of winning. The aim of this study is to address these questions by investigating battles in a social insect, the red wood ant Formica rufa. These ants are common in the southern UK but their status is less secure across the whole of their European range. To investigate the ways that fighting ability and fighting behaviour influence how strongly differences in group size should affect the outcome of battles, we will use approaches that have been developed during studies of fights between pairs of individual animals. These will include measuring body size, weapon size and the energy status of combatants in opposing groups. By studying this species of ant we aim to draw conclusions of general relevance that will improve our understanding of aggressive behaviour in animals in general and particularly of aggression between groups. The species chose is also classed as 'vulnerable' by the IUCN and knowing more about its biology and behaviour may aid in the conservation of this species that is native to the UK.

Much theoretical and empirical effort has been devoted to understanding how factors such as RHP and motivation should influence aggressive behaviour in animals, from the view-points of both contest dynamics and contest outcomes. The vast majority of this effort has been focussed on understanding pair-wise agonistic encounters or 'fights'. Empirical studies have focussed on analysing the effects of variation in resource value and RHP on the outcome of these encounters. Variables analysed include body size, strength, weapon size and energetic status of the opponents. However, contest behaviour is not restricted to pair-wise encounters and in social animals may occur between opposing groups. Models predicting the effects of group size and average RHP of group members were developed for human conflict and have been applied to cases of animal group conflict. These models were recently extended with the aim of accounting for key differences in the effects of RHP expected in human and animal conflicts. The primary aim of the proposed work is to test the assumptions and predictions of the updated theoretical framework. The secondary aim is to advance our understanding of group-contests by extending approaches developed for the analysis of pair-wise contests to the case of group contests. This will involve analysis of key components of individual RHP, including weapon size and energetic status, and characterisation of individual agonistic encounters within the overall group-contest in terms of key theoretical models of pair-wise encounters. We will also generate new ESS models of group conlifct, which will be informed by the findings of these studies.