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Discussion

Based on the data it appears that the hierarchy change observed in March of 2017 remains within this group. Table 1 and Figure 3 both back this up by clearly showing that Timbi, the dominant male, expressed authority over both Mama and Tumani through the comparatively high number of dominances in agonistic encounters observed. Tumani's position in the middle of the social hierarchy can be seen through her high number of dominances over Mama but only one successful challenge over Timbi. Mama's position at the bottom of the hierarchy is clear since she was never observed to have dominated Timbi and was only successful twice in dominating Tumani. The linear hierarchy seen through the data is also consistent with behaviors observed in the wild since linear hierarchies are isolated to simians in the Cercopithcinae subfamily, which includes this species (Welker 1985).

After viewing the hierarchy in terms of dominance, it is also notable that Timbi would step in to assist Tumani in dominating Mama on a consistent basis. This is primate behavior seen in the wild where the entire group works together to enforce a hierarchy through gestures and expressions to influence the social status of an individual throughout their life (Lewis et al. 2013). It is possible that the times Timbi stepped in to enforce the hierarchy were an attempt to prevent the threat displays between Mama and Tumani from escalating into a physical confrontation. Such de-escalation behavior has been documented as an important role of the dominant male in wild Cercopithecus species, in which the male uses subtle agnostic expressions to prevent fights and keep order within the group (O'Neil 2012). There were two documented cases of Mama expressing dominance over Tumani, however, they did not appear to be escalating beyond threat displays like the cases where Timbi stepped in to help Tumani dominate Mama.

The dominant male's role as the leader and protector of the group was also observed in alarm call behavior. This alarm call was rarely observed during the observation period. It was only recorded twice and were responses to loud thunder in the area. Timbi was the one giving the alarm call for both instances. This observation is consistent with observations made on Cercopithecus species in the wild. According to a study conducted by Papworth on Cercopithecus mitus stuhlmanni, the males within the group were the ones to deliver the alarm call. Papworth suggests that this is because males undergo natal dispersal as adolescence and afterwards need to maintain dominance over their new social group. Even though being the producer of the alarm call puts the dominant male at greater risk of predation, it is in his biological interest to protect his group. If he were to lose his group in a predator attack, the male would have to either reestablish himself as the dominant male of a different group or directly compete with another dominant male for control of a group (Papworth et al. 2008).

Based on my observations, it seems that many of these aggression incidents were sparked by food. Timbi was particularly aggressive about food, chasing around Mama and Tumani if they found a food source he was not aware of. Tumani also instigated agnostic fights over food but only with Mama, following the social hierarchy. This observation is consistent with the observations documented by Hirsch on foraging behavior and spacial positioning in Cercopithecus with the more dominant individuals claiming desired food patches (Hirsch 2007). Another observation on foraging that was consistent with this model was seen in the positioning of the three guenons when eating. It was commonplace to see all three eating in opposite corners of the enclosure, which follows from the predicted dispersal of individuals preferring the edge of the group.

During these agnostic encounters, however, it was not observed that any of the specimens used their cheek pouches to secure food from their aggressors as seen in other guenon species. This apparent abnormality runs consistent with a study on cheek pouch usage conducted by Buzzard. The spot-nosed guenon was the only species where an increase in cheek pouch usage was not observed with the introduction of more competition for food. This effect even included direct competition with Diana monkeys, a particularly aggressive species of Cercopithecus (Buzzard 2006). This trend was explained through the foraging and antipredator behaviors of C. petaurista. Compared to other species under Cercopithecus, C. petaurista consumes less fruit and is more of a folivore. In Buzzard's study guenon species that were primarily frugivores had the highest degree of cheek pouch usage than those that were not. When looking at antipredator behavior, C. petaurista uses crypsis to hide amongst the dense foliage of its surrounding environment. Other species of Cercopithecus rely more on group defense among multiple species. Group defense may, in turn, lead to a higher use of cheek pouches because of the more aggressive antipredator defense strategy that incentivizes movement over staying in one space and increased competition because of the dependence on colonies of other species for a group defense and the benefits of the dilution effect in a larger group of individuals (Buzzard 2006). This may also be the reason why there was a significant amount of aggression surrounding food since competition for this species in the wild is primarily intraspecific instead of interspecific.

The data also shows that social hierarchy holds influence over social grooming. When looking at each specimen, figure 5 shows that each individual spent more time on average grooming an individual with a higher social status than they did receiving grooming from that same individual. For example, between Tumani and Mama, Mama spent 10.625 minutes on average grooming Tumani while only receiving 7.53 minutes of grooming. Another trend to note is that number of observations on grooming received parallels the rank along the social hierarchy. Timbi was observed to receive the most grooming at 37 times total, followed by Tumani at 24 times total. Mama was observed to receive grooming the least amount of times at 17 times total. These observations are consistent with a model of grooming developed by Robert Seyfarth, which predicts female members of adjacent ranks within a social hierarchy are more likely to be grooming partners (Seyfarth 1977). This pattern occurs because members of a community desire to groom with those that hold a higher social status to gain access to some of their privileges, but at the same time, such a patter complicates with competition for these highranking grooming partners. This combination of factors makes grooming with the next adjacent rank the most likely and socially reinforced grooming option (Tiddi 2012). While the results of testing this model have been mixed, there is substantial evidence that the model works well in species with a strong, linear hierarchy (a trait of the Cercopithcinae subfamily) and that there is a connection between social status, being a desirable grooming partner, and competition over grooming partners (Vila 2015). One result of this model is that since higher social rank makes a group member a more desirable grooming partner, a highest-ranking member like Timbi receives more grooming opportunities than those lower in rank. The number of times grooming was received continued to reflect the hierarchy when looking at Tumani and Mama since desirability as a partner decreases along with social status.

Another way the data lines up with the Seyfarth Model can be seen in Figure 5. While Mama and Tumani groomed the lowest number of observed times, they groomed for a longer average time than any other pair. On more than one occasion, Tumani ended grooming between Mama and Timbi with agonistic behaviors such as chasing Mama away from Timbi or carrying out a threat display using agonistic facial expressions and posture. To further support the Seyfarth Model in action, no other grooming pair was observed to be interrupted and separated through dominance challenges. Since the only other grooming pairs possible are made up of individuals of adjacent rank, this result is consistent the Seyfarth Model.

According to Figure 6, both Tumani and Mama received grooming for a longer amount of time than Timbi. This observation is due to a higher level of reciprocal grooming between females of the Cercopithcinae subfamily (Vila 2015). Properties of the Seyfarth Model may have exaggerated this trend further since Tumani and Mama were both the only two females in the group and adjacent in rank.

While most of the grooming data seems to directly follow the hierarchy, two pieces of data conflict with the rest. Figure 6 shows that the amount of time grooming was received on average runs opposite to the dominance hierarchy. Based on the literature and the data, I believe that this is the result of several different factors at work. First was the high level of reciprocal grooming between Mama and Tumani. Whenever Tumani would solicit grooming from Mama, it was almost always a case of reciprocal grooming. Timbi, in comparison, participated in a very low degree of reciprocal grooming possibly encouraging Mama to groom Tumani more often since she was more likely to receive grooming in return. Second was the effects of the dominance hierarchy through the lens of the Seyfarth Model. For the most part, Mama was limited to grooming with Tumani due to social rank. In the times where Mama would groom with Timbi, Tumani would put on a threat display to challenge Mama. Since Mama could not challenge Tumani back, these grooming sessions would usually end with Mama running away in submissive manner. Because of these aggressive encounters between Mama and Tumani in particular, Tumani would groom Mama as a means of reconciliation (Puga-Gonzalez et al. 2009).

Conclusion>>