Costs dictate strategic investment in dominance interactions

Dominance is important for access to resources. As dominance interactions are costly, individuals should be strategic in whom they interact with. One hypothesis is that individuals should direct costly interactions towards those closest in rank, as they have most to gain—in terms of attaining or maintaining dominance—from winning such interactions. Here, we show that male vulturine guineafowl ( Acryllium vulturinum ), a gregarious species with steep dominance hierarchies, strategically express higher-cost aggressive interactions towards males occupying ranks immediately below themselves in their group's hierarchy. By contrast, lower-cost aggressive interactions are expressed towards group members further down the hierarchy. By directly evaluating differences in the strategic use of higher- and lower-cost aggressive interactions towards competitors, we show that individuals disproportionately use highest-cost interactions—such as chases—towards males found one to three ranks below themselves. Our results support the hypothesis that the costs associated with different interaction types can determine their expression in social groups with steep dominance hierarchies. This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’.

Costs dictate strategic investment in dominance interactions

Dominance is important for access to resources. As dominance interactions are costly, individuals should be strategic in who they interact with. One hypothesis is that individuals should direct costly interactions towards those closest in rank, as they have most to gain--in terms of attaining or maintaining dominance--from winning such interactions. Here, we develop a novel analytical framework to test whether interactions are directed strategically in relation to rank differences, and use these to compare strategies across types of interactions that vary in cost. We show that male vulturine guineafowl (Acryllium vulturinum), a gregarious species with steep dominance hierarchies, strategically direct costly interactions towards males occupying ranks immediately below themselves in their group's hierarchy. In contrast, low-cost interactions are not directed towards closest competitors, but towards group members slightly further down the hierarchy. We then show that, as a result of the difference in strategic use of high- and low-cost interactions towards closest competitors, individuals disproportionately use highest-cost interactions--such as chases--towards males found one to three ranks below them. Our results support the hypothesis that the costs associated with different interaction types can determine their expression in social groups.

Preschoolers do not generalize dominance roles from one situation to another

Recognizing social rank as a third-party observer is an important social skill. With regard to dominance—the coercive form of social rank—infants expect the winner of a zero-sum conflict over one type of resource to win again when competing with the same agent over a different type of resource (Mascaro & Csibra, 2012). However, it is unclear whether preschoolers also expect dominant-subordinate roles to generalize across situations. The current study tested this question with preschoolers (3-5 years, n = 280, 140 female, USA, 80% White) and adults (n = 200, 99 female, USA, 75% White). Preschoolers and adults recognized the dominant puppet in two resource conflict situations (a toy to play with, a bench to sit on) in which one puppet won by force and the other lost (Exp. 1). Preschoolers did not expect the puppet who had been dominant in one situation (e.g. toy) to win again in a new situation (e.g. bench) (Exp. 2a and 2b). Adults, like infants, thought the dominant puppet would win again (Exp. 2b). When the concepts of dominance and fairness were primed (Exp. 3), preschoolers’ inferences about the winner diverged: Children who had been primed with dominance thought the subordinate would win, while those who had been primed with fairness responded at chance level. This finding, together with converging support from children’s justifications, suggests that preschoolers are particularly sensitive to the unfairness of dominance interactions, and indicates that this consideration affects their inferences about the stability of dominance.

How feedback and feed-forward mechanisms link determinants of social dominance

In many animal societies, individuals differ consistently in their ability to win agonistic interactions, resulting in dominance hierarchies. These differences arise due to a range of factors that can influence individuals’ abilities to win agonistic interactions, spanning from genetically driven traits through to individuals’ recent interaction history. Yet, despite a century of study since Schjelderup-Ebbe’s seminal paper on social dominance, we still lack a general understanding of how these different factors work together to determine individuals’ positions in hierarchies. Here, we first outline five widely studied factors that can influence interaction outcomes: intrinsic attributes, resource value asymmetry, winner-loser effects, dyadic interaction-outcome history and third-party support. A review of the evidence shows that whilst different factors have been shown to be important in specific systems, there are few empirical cases where one factor has a definitive effect. We then propose that mixed empirical support for a single factor is likely to arise due to feedback loops, whereby the outcomes of previous agonistic interactions (e.g. access to food) impact factors that might be important in subsequent interactions (e.g. body condition). We provide a conceptual framework which illustrates that there are many potential routes through which feedbacks can occur. Such feedbacks suggest that the factors that determine outcomes of dominance interactions are highly intertwined and are likely to rarely act independently of one-another. Further, we generalise our framework to include multi-generational feed-forward mechanisms and highlight how interaction outcomes in one generation can influence the factors determining interaction outcomes of their offspring via a range of parental effects. This general framework describes how interaction outcomes and the factors determining them are linked within generations via feedback loops, and between generations via feed-forward mechanisms. We then highlight methodological approaches that will facilitate the study of feedback loops and dominance dynamics. Lastly, we discuss how our framework can shape future research, including investigating how feedbacks in dominance hierarchies produce ‘self-organised’ structure, exploring how interaction outcomes are integrated to form dominance hierarchies, and the routes of parental influence on the dominance status of offspring. Ultimately, by considering dominance interactions as part of a dynamic system, that also feeds forward into subsequent generations, we will better understand the factors that structure dominance hierarchies in animal groups.

Effects of social experience, aggressiveness and comb size on contest success in male domestic fowl

The ability to dominate conspecifics and thereby gain access to resources depends on a number of traits and skills. Experience of dominance relationships during development is a potential source of learning such skills. We here study the importance of social experience, aggressiveness and morphological traits for competitiveness in social interactions (contest success) in male domestic fowl ( Gallus gallus domesticus ). We let males grow up either as a single (dominant) male or as an intermediately ranked male in a group of males, and measured their success in duels against different opponents. We found that single-raised males had lower contest success than group-raised males, and that aggression and comb size correlated positively with contest success. This indicates that experience of dominance interactions with other males increases future success in duels. We similarly studied the consequences of growing up as a dominant or subordinate in a pair of males, finding no statistically significant effect of the dominance position on contest success. Finally, we found that males were consistent over time in contest success. We conclude that social experience increases contest success in male domestic fowl, but that certain behavioural and morphological characteristics have an equal or even stronger covariation with contest success.

Modeling Network Dynamics

Given that social networks are inherently dynamic phenomena, characterizing their structure, precursors, and consequences can be improved by methodologies that incorporate such dynamism. This chapter discusses several longitudinal network modeling approaches that seek to understand the process of network change, on one hand, and to predict future network states, on the other. These include the relational event model (REM), exponential random graph model (ERGM), and stochastic actor-oriented model (SAOM). These models focus on different temporal resolutions and differentiate instantaneous events from relations with longer durations, among other distinctions. The chapter identifies commonalities and unique features of each model, both conceptually and via an application to a longitudinal network dataset of dominance interactions within a herd of Eurasian red deer. Throughout, the chapter emphasizes each modeling framework’s assumptions, data requirements, and parameter and model interpretation.

A place for everything and everything in its place: spatial organization of individuals on nests of the primitively eusocial wasp Ropalidia marginata

Non-random space use is common among animals across taxa and habitats. Social insects often use space non-randomly, outside as well as inside their nests. While such non-random space use outside the nest may improve foraging efficiency, inside the nest, it is often associated with the efficient division of labour. Non-random space use by adults on their nests has been hypothesized to result from dyadic dominance interactions, non-random distribution of tasks, differential activity levels, workers avoiding their queens or prophylactic avoidance of disease spread. These hypotheses are generally derived from species in which the tasks of the workers are themselves non-randomly distributed on the nest. Here, we study the primitively eusocial wasp Ropalidia marginata , in which tasks are not distributed non-randomly, and show that 62.4% ± 16.2% of the adults nevertheless use space on their nest non-randomly. In this species, we find that non-random space use may help optimizing nutritional exchange between individuals while prophylactically minimizing disease spread among nest-mates. We did not find evidence for the roles of dominance interactions, activity levels or location of larvae in non-random space use. Spatial organization appears to be a mechanism of minimizing the costs and maximizing the benefits of social life.

Elevated aggression is associated with uncertainty in a network of dog dominance interactions

Dominance hierarchies are widespread in animal societies and reduce the costs of within-group conflict over resources and reproduction. Variation in stability across a social hierarchy may result in asymmetries in the benefits obtained from hierarchy formation. However, variation in the stability and behavioural costs of dominance interactions with rank remain poorly understood. Previous theoretical models have predicted that the intensity of dominance interactions and aggression should increase with rank, but these models typically assume high reproductive skew, and so their generality remains untested. Here we show in a pack of free-living dogs with a sex–age-graded hierarchy that the central region of the hierarchy was dominated by more unstable social relationships and associated with elevated aggression. Our results reveal unavoidable costs of ascending a dominance hierarchy, run contrary to theoretical predictions for the relationship between aggression and social rank in high-skew societies, and widen our understanding of how heterogeneous benefits of hierarchy formation arise in animal societies.

Dominance and aggression in captive gidgee skinks (Egernia stokesii)

Dominance is a key component of behaviour in many animal species and is central to social system dynamics, resource acquisition, individual fitness and ultimately reproductive success. We investigated dominance interactions and social behaviours in a group of captive juvenile gidgee skinks (Egernia stokesii). We hypothesised that a dominance hierarchy existed within the group, and that aggressive behaviours would be used to secure limited resources, especially high-value resources. We also hypothesised that body weight would be positively correlated with dominance and aggressive behaviours. We filmed the lizards at 1200 hours for six days a week over the course of eight weeks. We exposed the lizards to three different diets, which consisted of an animal-based diet (crickets), plant-based diet (plants), and a non-feeding control (no food offered). The relative value of these resources to the skinks was established through preference tests. We identified a dominance hierarchy, with dominant individuals exhibiting more aggressive behaviours than subordinates. We found that the frequency of aggressive behaviours was significantly higher in trials where high-valued resources (crickets) were at stake. Furthermore, we found a significant positive correlation between body weight and dominance, bite and chase; larger individuals were ranked higher in the social hierarchy compared to smaller individuals. Our results demonstrate the importance of morphological and behavioural traits in determining a dominance hierarchy in E. stokesii and how dominance can have ecological advantages.

Concede or clash? Solitary sharks competing for food assess rivals to decide

To adapt to their environment, organisms can either directly interact with their surroundings or use social information (i.e. information provided by neighbouring individuals). Social information relates to the external features of surrounding peers, and little is known about its use by solitary species. Here, we investigated the use of social cues in a solitary marine predator by creating artificial aggregations of free-ranging sicklefin lemon sharks ( Negaprion acutidens ). Using a novel monitoring protocol, we analysed both dominance interactions and tolerance associations between sharks competing for food in relation with the number, the morphology and the behaviour of rivals. Sharks produced more agonistic displays and spent more time around the bait as competitors were more abundant. Moreover, the morphological attributes of competitors had very limited influence on the structure of shark social interactions. Instead, sharks appeared to establish tolerance relationships with competitors according to their individual behaviour. Furthermore, the more two sharks were observed together at a given study site, the fewer agonistic interactions they exchanged. We discuss these findings as evidence of the use of social cues in a non-gregarious predatory species and suggest directions for future research.