When two or more animals use limited amounts of resources, such as food, mates, or shelter, competition may occur. Individuals may gain access to the same resources when the resources can be shared, or some individuals may retreat and find other resources to avoid direct conflict. However, when one or more individuals take forceful action to monopolize resources (or claim a larger share than other individuals), aggression may occur. Individuals also use aggression to increase their social status which may influence their reproductive success (Clutton-brock 1988). Investigating patterns of aggression, such as frequency, severity, and context, is a useful tool to understand the social system of a species, social relationships among individuals, and the environment in which the individuals live.

Conclusion

Bonobos use aggression in various contexts, which may influence their social system, and vice versa. Although aggression can sometimes be fierce, the risk of aggression is lower than that in chimpanzees. Such a low risk of aggression may lead to increased possibilities of being together, communicating with each other, and promoting gregariousness and affiliative social interactions. Affiliative social interactions may promote tolerance among group members and decrease the risk of aggression.
Different degrees of feeding and mating competition are considered important factors for differences in behavioral tendencies between the two Pan species, including patterns of aggression. Relaxed feeding competition in bonobos might have enabled females to be more gregarious and form coalitions, which led to their high social status in the group (Parish 1994; Furuichi 2011; Hare, Wobber and Wrangham 2012; Tokuyama and Furuichi 2016). Males might not employ strategies that use aggression toward females to increase their reproductive success, because such attempts may easily be countered by female coalitions. The high social status of females might also enable mothers to intervene in male–male aggression to support their sons, decreasing the importance of direct competition among males over social rank (Furuichi 1997, 2011, 2023). However, all previous studies on female bonobo association, coalition formation, social dominance, and feeding competition have been conducted in dense forests. Bonobos inhabiting diverse environments, from dense forests to forest-savanna mosaics, where food abundance is relatively low and detailed behavioral observations have not yet been conducted (Narat et al. 2015; Serckx et al. 2016). Detailed comparisons of bonobo behavioral patterns, including aggression, in different environments are required to draw concrete conclusions.
Female bonobos have a prolonged period of sexual acceptability, where their sexual swellings reach maximal tumescence not only when they are cycling, but also during pregnancy and lactation, whereas only cycling females exhibit maximal swelling in chimpanzees (Furuichi 1987; Douglas et al. 2016; Ryu et al. 2022; but see Deschner and Boesch 2007 in which non-cycling females may exhibit maximal swelling in Taï chimpanzees). This might lower the male monopolization potential of females and allow males to invest less in female defense, which might lead to the moderate level of male competition in bonobos (Furuichi 1987, 2011). However, higher-ranking males copulate more frequently than lower-ranking males (Surbeck et al. 2010), and higher-ranking males copulate more often with females with high fertility than lower-ranking males do (Ryu et al. 2022; Yokoyama and Furuichi 2022). In addition, the reproductive skew by dominance rank among males is higher than that of chimpanzees (Surbeck et al. 2017; Ishizuka et al. 2018), indicating that the potential of male monopolization of females is higher in bonobos than in chimpanzees. Further studies that carefully investigate the reproductive status of females, copulation, and patterns of aggression among males are required to clarify whether prolonged periods of female sexual acceptability reduce mate competition among male bonobos.