Lit Review, 5. Group and Social Contests

While the majority of contest theory has focused on dyadic interactions between two individuals, recent work has begun to apply these frameworks to group-level and social conflicts. This extension is important, as many species engage in collective conflicts that cannot be fully captured by models developed for one-on-one fights. Intergroup conflicts are widespread across taxa, from border disputes between chimpanzee communities to territorial battles in social carnivores like lions and wolves (Green et al., 2021). Similarly, social insects like ants engage in colony-level territorial contests that can be viewed through the lens of contest theory (Hölldobler & Wilson, 2009). Here, we explore how contest theory can inform our understanding of intergroup conflicts and social insect colony contests, and discuss the unique challenges and opportunities presented by these more complex scenarios.
Many of the core concepts from dyadic contest theory, such as resource holding potential (RHP) and mutual assessment, can be applied to intergroup conflicts with some modifications (Green et al., 2021). Group RHP may be determined by factors like group size, composition, and collective fighting ability. Assessment strategies in group contests might involve comparing relative group sizes or gauging the strength of collective displays. Group size is often the strongest predictor of success (Majolo et al., 2020), but within-group heterogeneity can add complexity. For example, groups with more males can overcome a group size disadvantage in some species like grey wolves (Cassidy et al., 2015). Social cohesion could also serve as a proxy for group RHP, with more coordinated groups potentially having a competitive edge (Green et al., 2021). This could be measured through temporal and/or spatial coordination of group member behaviors or other metrics.
Intergroup conflicts also introduce unique dynamics not present in dyadic contests, such as greater potential for free-riding and the need for within-group coordination (Green et al., 2021). Heterogeneity among group members in traits like size, strength, and the value they place on the contested resource can lead to collective action problems, where not all individuals participate equally despite success depending on collective effort. Mechanisms like punishment, social incentives, and coercion by dominant individuals may help overcome these challenges and promote group-level cooperation (Arseneau-Robar et al., 2016, 2018). For example, in some primate species, females reward fighting males with affiliative behavior (Arseneau-Robar et al., 2016). Integrating these factors into contest models will be key for advancing our understanding of intergroup conflict resolution.
The application of dyadic contest theory to intergroup conflicts can also be seen in the use of Lanchester's laws (Green et al., 2021). Lanchester's linear law should be followed if the more numerous side matches the number of combatants allocated by the less numerous side, while Lanchester's square law would be followed if the more numerous side commit their extra numbers to the fray, such that members of that side can concentrate their attacks on the outnumbered members of the weaker side. Testing these predictions in group contests could provide insights into the dynamics and determinants of intergroup conflict outcomes.
Social insects provide another fascinating context for studying group-level contests. Ant colonies can be viewed as "superorganisms" that engage in territorial battles with other colonies (Hölldobler & Wilson, 2009). Reeve and Hölldobler (2007) propose that competition between colonies has promoted the evolution of cooperative groups that are so tightly integrated they can be considered a single organism. Within this framework, assessment strategies, fighting ability, and the evolution of competitive traits can be examined at the colony level. Chapin et al. (2022) found that ant colonies altered their fighting effort based on the relative number of workers in the opposing colony, suggesting colony-level mutual assessment. Colonies also increased aggression when facing opponents with relatively more brood (a valuable resource), indicating resource value assessment (Chapin et al., 2022). These findings suggest that contest theory concepts can be meaningfully applied to colonial organisms, though the mechanisms underlying colony-level assessments remain unclear.
The role of individual differences within groups is another important consideration. In many social species, individuals vary in fighting ability, boldness, and other traits that could influence their contribution to group contests (Briffa et al., 2015; Palaoro & Peixoto, 2022). For example, in the ant Cataglyphis niger, majors assess opponent fighting ability while minors always flee (Nowbahari et al., 1999). Understanding how these individual differences scale up to shape group-level strategies is an important avenue for future research.
Examining group-level competitive interactions and the cognitive mechanisms underlying strategic decisions in social conflicts can provide new insights into the evolution of social behavior and cognition (Reichert & Quinn, 2017). Although evidence abounds for a role of cognition in contests, most studies focus only on demonstrating information gathering and use. The mechanisms by which this information is processed, retained, and used in decision making are rarely investigated and largely treated as a black box by both empiricists and theoreticians (Reichert & Quinn, 2017). Addressing this gap will be crucial for advancing our understanding of the cognitive drivers of contest behavior and their evolutionary implications.
Future research on intergroup and social contests will benefit from adapting the well-established models and approaches used for dyadic contests. However, the added complexity of these interactions, such as group size and fluidity, within-group heterogeneity, and collective action problems, introduce new challenges and opportunities for both theoretical and empirical work. Integrating these factors into contest models and empirically testing their predictions will be crucial for advancing our understanding of conflict and cooperation in social animals. Overall, the study of group and social contests represents an exciting new direction in animal contest research that bridges multiple levels of analysis and has the potential to provide novel insights into the evolution of social behavior, cognition, and cooperation.