Hierarchies in a Troop of Captive Squirrel Monkeys

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An observation investigation into whether or not dominance hierarchies exist in a troop of Captive Squirrel monkeys

Darwin (1859, as cited in Darwin, 1909) proposed the idea that species of animals have evolved through survival of the fittest and in doing this form a social group in order to increase their chances of survival against predation. Drews (1993) defined dominance hierarchies as the pattern of repeated, agonistic interaction between two individuals, characterised by a consistent outcome in favour of the same dominant member and a default submissive response of its opponent rather than escalation, further developed by Cole (1981) who suggested that dominance hierarchies are characterised by routine displays of dominance, avoidance behaviours, and even fighting. A social hierarchy arises when members of a social group interact, often aggressively in order to create a ranking system. Within this ranking, individuals compete against each other for limited resources and the chances to mate. Alonso et al. (2012) proposed that during the reproductive season, some species establish a social dominance hierarchy which determines their access to resources and reproduction for individuals of the highest rank. Alonso et al also observed that, particularly in males, that ranking of dominance is relative to the size of the individual, and that in females, aggressiveness and reproductive ability determine the rank of an individual. The dominance hierarchies displayed in primate groups suggest that higher-ranking males have the highest reproductive success due to increased female attention and availability. Female primates at a higher level benefit and are able to produce more surviving offspring, (Huntingford and Turner, 1987). In relation to Darwin’s sexual selection theory, Huntingford and Turner’s theory suggests that the advantageous genes of higher level females are able to be passed on, and will therefore benefit the next generation of the group of which have increased chances of survival, and are stronger with better fitness abilities (Samuels, Silk and Rodman, 1984). This observation is to be conducted on a troop of captive Squirrel monkeys in an English zoo, of which live together in multi-male and multi-female troops (Walker, Anderson, Herndon and Walker, 2009).

The aim of this research is to devise whether or not a dominance hierarchy exists within a troop of captive primates.

Table 1: Table displaying the frequency of behaviours shown by different captive Squirrel Monkeys. Monkey| Dominant| Neutral| Submissive|
1| 39| 25| 0|
2| 10| 47| 7|
3| 9| 26| 29|

From table 1, it can be seen that monkey 1 displayed no submissive behaviours, and more than double the number of dominant behaviours performed by monkeys 2 and 3. Monkey 3 showed noticeably more submissive behaviours than the other two observed monkeys. Although results for monkey 3 were close in neutral and submissive actions, monkey 2 displayed more neutral behaviours throughout the observation period.


Fig.1 : Graph to show the frequencies of different behaviours each captive monkey displayed It can be seen from the skew to the left in figure 1, that monkey 1 displayed more dominant behaviours, especially more aggressive behaviours such as verbal aggression, chasing and pushing, in comparison to monkeys 2 and three and displayed no submissive behaviours. On the other hand, monkey 3 displayed no dominant behaviours, and skews further to the right, suggesting that more submissive behaviours were shown in response to monkey 1. Monkey 2 shows a large central peak, suggesting that this monkey’s actions were very neutral in relation to monkey 1 and monkey 3’s behaviours. In order to determine whether there was a level of significance in the results, a Chi-Squared test was conducted, from which it can be seen that there was a significant difference between the monkeys,...
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