Intergroup Contests Research Articles

Pattern of individual participation and cheating in conflicts between groups of free-ranging dogs

Cooperative intergroup aggression provides an example of a costly cooperative behaviour whose benefits spill over to noncooperative animals as well. Consequently, investigating factors that promote individual participation in intergroup contests should prove useful for understanding how cooperation may persist in animal societies despite cheating. Here, we examined variables affecting individual participation in naturally occurring conflicts between groups of free-ranging dogs, Canis lupus familiaris . The overall proportion of cooperating group members decreased significantly with an increasing number of group members present. In one pack, the individual probability of active participation decreased significantly when this pack had a numerical advantage over opponents. Dogs belonging to the smallest pack tended to be more cooperative than those belonging to larger groups. Social prestige (measured as the number of submissions received during greeting) did not appear to be a consequence of cooperative behaviour. Individual participation increased with an increasing number of affiliative partners. Young and high-ranking dogs tended to cooperate more when their group was outnumbered by opponents but did not stay at the front of the pack during conflicts. These results emphasize the greater opportunity for cheating in larger groups and the complexity of dogs' behaviour. Cooperation appears to be conditional on both the ‘adversity of the environment’ (as measured by relative group size) and the identity/behaviour of companions.

Multiple resource values and fighting ability measures influence intergroup conflict in guerezas ( Colobus guereza)

Intergroup conflict occurs in many social species and involves potentially complex motivations and interactions. To understand its complexity in wild animals more fully, a comprehensive investigative approach is needed, in which the multiple resource values and measures of fighting ability that potentially influence intergroup contests are simultaneously considered and controlled for. This study uses long-term data on eight neighbouring groups of folivorous black and white colobus monkeys, Colobus guereza (‘guerezas’) in Kibale National Park, Uganda, to investigate the factors influencing intergroup conflict. Adult males were the main participants in intergroup aggression. Of the three resource values investigated, food value had the most unambiguous positive effect on the tendency for males to initiate high-level intergroup aggression and for groups to win. Mate value positively influenced male initiation of high-level intergroup aggression, but not more so for the group that contained high-value mates. The presence of young infants had no obvious effects. Unlike in many other species, males were more likely to initiate intergroup aggression if their groups were smaller and contained fewer adult males than opposing groups. Groups with fewer but larger adult males, and to some extent, smaller groups, were more likely to win encounters. Moreover, the relative number of adult males/group largely affected the degree to which some other factors influenced male initiation of aggression and contest outcome. These findings reveal that a complex interplay between multiple resource values and multiple fighting ability measures can simultaneously influence initiation of and success in intergroup conflict.

Interaction location outweighs the competitive advantage of numerical superiority in Cebus capucinus intergroup contests.

Numerical superiority confers a competitive advantage during contests among animal groups, shaping patterns of resource access, and, by extension, fitness. However, relative group size does not always determine the winner of intergroup contests. Smaller, presumably weaker social groups often defeat their larger neighbors, but how and when they are able to do so remains poorly understood. Models of competition between individuals suggest that location may influence contest outcome. However, because of the logistical difficulties of studying intergroup interactions, previous studies have been unable to determine how contest location and group size interact to shape relationships among groups. We address this question by using an automated radio telemetry system to study intergroup interactions among six capuchin monkey (Cebus capucinus) social groups of varying sizes. We find that the odds of winning increase with relative group size; one additional group member increases the odds of winning an interaction by 10%. However, this effect is not uniform across space; with each 100 m that a group moves away from the center of its home range, its odds of winning an interaction decrease by 31%. We demonstrate that contest outcome depends on an interaction between group size and location, such that small groups can defeat much larger groups near the center of their home range. The tendency of resident groups to win contests may help explain how small groups persist in areas with intense intergroup competition.

Long-distance calls in Neotropical primates.

Long-distance calls are widespread among primates. Several studies concentrate on such calls in just one or in few species, while few studies have treated more general trends within the order. The common features that usually characterize these vocalizations are related to long-distance propagation of sounds. The proposed functions of primate long-distance calls can be divided into extragroup and intragroup ones. Extragroup functions relate to mate defense, mate attraction or resource defense, while intragroup functions involve group coordination or alarm. Among Neotropical primates, several species perform long-distance calls that seem more related to intragroup coordination, markedly in atelines. Callitrichids present long-distance calls that are employed both in intragroup coordination and intergroup contests or spacing. Examples of extragroup directed long-distance calls are the duets of titi monkeys and the roars and barks of howler monkeys. Considerable complexity and gradation exist in the long-distance call repertoires of some Neotropical primates, and female long-distance calls are probably more important in non-duetting species than usually thought. Future research must focus on larger trends in the evolution of primate long-distance calls, including the phylogeny of calling repertoires and the relationships between form and function in these signals.

Chimpanzees and the mathematics of battle.

Recent experiments have demonstrated the importance of numerical assessment in animal contests. Nevertheless, few attempts have been made to model explicitly the relationship between the relative number of combatants on each side and the costs and benefits of entering a contest. One framework that may be especially suitable for making such explicit predictions is Lanchester's theory of combat, which has proved useful for understanding combat strategies in humans and several species of ants. We show, with data from a recent series of playback experiments, that a model derived from Lanchester's 'square law' predicts willingness to enter intergroup contests in wild chimpanzees (Pan troglodytes). Furthermore, the model predicts that, in contests with multiple individuals on each side, chimpanzees in this population should be willing to enter a contest only if they outnumber the opposing side by a factor of 1.5. We evaluate these results for intergroup encounters in chimpanzees and also discuss potential applications of Lanchester's square and linear laws for understanding combat strategies in other species.

BEHAVIOR ANALYSIS APPLIED TO ENVIRONMENTAL/ECOLOGICAL PROBLEMS; A REVIEW1

Recent applications of operant technology, including the manipulation of environmental conditions and response consequences, have been directed toward the improvement of man‐environment relations. This document summarizes the research designs, procedures, results, and conclusions of these recent behavioral interventions for ecological rebalance. Each of the 32 studies reviewed was undertaken since 1970; all studies were relatively successful in changing the probability of an ecology‐related response; all studies incorporated basic methodologies applicable for large‐scale, community programs; most of the investigations were conducted in field settings (e.g., college campuses, grocery stores, mobile‐trailer parks, homes, movie theaters, public campgrounds, and a football stadium). Several of the studies are as yet unpublished. Sources for receiving documentation of the unpublished research are provided in this document. About 50% of the investigations reviewed were designed to influence behaviors related to environmental litter; the others were of behavior‐modification programs that substantially increased bus‐ridership, decreased lawn‐trampling, promoted the purchase of drinks in returnable rather than throwaway containers, initiated a recycling process, or reduced energy consumption. Essentially, the interventions were either preventive in nature (i.e., designed to discourage environment‐destructive behaviors before they occur), or remedial (i.e., designed to encourage behaviors that correct an existing environmental problem). Usually, the preventive measures emphasized responses priming (or prompting), while the corrective measures applied some form of positive reinforcement. Response priming was accomplished with modelling techniques, or with written and/or verbal prompts presented either publicly or on a personal, one‐to‐one basis. Among the positive reinforcement procedures were field applications of token economies, lottery systems, feedback programming, and intergroup contests, as well as individual contingency contracting. Some experimental designs provided for comparisons between the behavioral effects of response priming and positive reinforcement.