Self-organizing conflicts: Group assessment and the spatio-temporal dynamics of ant territory battles

Battles between ants (Hymenoptera: Formicidae): a review

With their unique colony structure, competition between ants (Hymenoptera: Formicidae) can be particularly intense, with colonies potentially willing to sacrifice large number of individuals to obtain resources or territory under the right circumstances. In this review, we cover circumstances in which ant competition escalates into combat, battle strategies and tactics, and analysis methods for these battles. The trends for when colonies choose to fight can vary greatly dependent on the species and situation, which we review in detail. Because of their large group sizes, ant conflicts can follow different patterns than many other species, with a variety of specialist adaptations and battle strategies, such as specialized worker classes and the need to rapidly recruit large number of compatriots. These same large group sizes also can make ant fighting amenable to mathematical analysis, particularly in the context of Lanchester's laws that consider how total numbers influence the outcome of a confrontation. Yet, dynamic behavior can often disrupt idealized mathematical predictions in real-world scenarios, even though these can still shed light on the explanations for such behavior. We also systematically cover the literature on battles between groups of ants, presenting several other interesting studies on species with unique colony organization, such as army ants and leafcutter ants.

From inter-group conflict to inter-group cooperation: insights from social insects

The conflict between social groups is widespread, often imposing significant costs across multiple groups. The social insects make an ideal system for investigating inter-group relationships, because their interaction types span the full harming-helping continuum, from aggressive conflict, to mutual tolerance, to cooperation between spatially separate groups. Here we review inter-group conflict in the social insects and the various means by which they reduce the costs of conflict, including individual or colony-level avoidance, ritualistic behaviours and even group fusion. At the opposite extreme of the harming-helping continuum, social insect groups may peacefully exchange resources and thus cooperate between groups in a manner rare outside human societies. We discuss the role of population viscosity in favouring inter-group cooperation. We present a model encompassing intra- and inter-group interactions, and local and long-distance dispersal. We show that in this multi-level population structure, the increased likelihood of cooperative partners being kin is balanced by increased kin competition, such that neither cooperation (helping) nor conflict (harming) is favoured. This model provides a baseline context in which other intra- and inter-group processes act, tipping the balance toward or away from conflict. We discuss future directions for research into the ecological factors shaping the evolution of inter-group interactions. This article is part of the theme issue 'Intergroup conflict across taxa'.

Mechanistic home range analysis reveals drivers of space use patterns for a non-territorial passerine

Home ranging is a near-ubiquitous phenomenon in the animal kingdom. Understanding the behavioural mechanisms that give rise to observed home range patterns is thus an important general question, and mechanistic home range analysis (MHRA) provides the tools to address it. However, such analysis has hitherto been principally restricted to scent-marking territorial animals, so its potential breadth of application has not been tested. Here, we apply MHRA to a population of long-tailed tits Aegithalos caudatus, a non-territorial passerine, in the non-breeding season where there is no clear 'central place' near which birds need to remain. The aim is to uncover the principal movement mechanisms underlying observed home range formation. Our foundational models consist of memory-mediated conspecific avoidance between flocks, combined with attraction to woodland. These are then modified to incorporate the effects of flock size and relatedness (i.e. kinship), to uncover the effect of these on the mechanisms of home range formation. We found that a simple model of spatial avoidance, together with attraction to the central parts of woodland areas, accurately captures long-tailed tit home range patterns. Refining these models further, we show that the magnitude of spatial avoidance by a flock is negatively correlated to both the relative size of the flock (compared to its neighbour) and the relatedness of the flock with its neighbour. Our study applies MHRA beyond the confines of scent-marking, territorial animals, so paves the way for much broader taxonomic application. These could potentially help uncover general properties underlying the emergence of animal space use patterns. This is also the first study to apply MHRA to questions of relatedness and flock size, thus broadening the potential possible applications of this suite of analytic techniques.