Female social relationships among wild Assemese macaques (Macaca assamensis)

Abstract

It has been repeatedly shown that strong, affiliative social relationships (hereafter “social relationships”) are extremely important for human health and well-being. Increasingly there is evidence that non-human species also form social relationships that share important characteristics of human social relationships: specifically differentiation in strength, stability and equality, and that these relationships play an important role in non-human fitness and well being. However, there have been strong criticisms of this work by some, who claim the apparent similarities between human and non-human social relationships may be by-products of very different, simpler processes. In addition, not all aspects of the proposed, shared characteristics have been thoroughly compared with their human equivalent. Investigations of non-human social relationships are also generally hindered by a lack of consensus on how best to quantitatively assess non-human social relationships. The overall aim of this thesis was to establish the characteristics of social relationships among wild, female Assamese macaques and consider how closely they resemble the characteristics of strong social relationships among humans and other non-human species. Specifically I addressed the criticisms and gaps in our understanding of the characteristics of non-human social relationships. In addition, I evaluated and made use of new quantitative measures of social behaviour, provided by Social Network Analysis (SNA) and considered whether these measures are helpful in improving our assessment of non-human social relationships. Data for this thesis were collected from a single group of wild Assamese macaques living within Phu Khieo Wildlife Sanctuary (16°5′–35′N, 101°20′–55′E), located in Chaiyaphum province, north-eastern Thailand. The sanctuary covers 1573km2 and is part of the regions contiguous ca. 6500 km2 Western Isaan Forest Complex. Data were collected over two one-year sampling periods (period 1: Oct. 2007 – Sep. 2008, period 2: May 2010 – Apr. 2011). During this time the group consisted of 49-53 individuals in total, 12 adult females in sampling period 1 and 15 adult females in sampling period 2. All adult females in the group were subject to regular focal observations, during which all social interactions were recorded using continuous sampling and general activity was recorded using instantaneous sampling. In total over 2100 hours of behavioural observations were collected. Analysis of this data revealed that female Assamese macaque social relationships do share some important characteristics of strong human social relationships. The social relationships were found to be strongly differentiated in strength, with females tending to only form a few stronger than average social relationships. Social relationships were also found toremain stable throughout the year, despite significant changes in the time females allocated to other behaviours, such as feeding and resting, associated with changes in the female breeding cycle. In addition, analysis also provided some initial evidence that these social relationships remain stable for several years. Females were also found to exchange services in an equitable manner, however unlike human social relationships, social relationships strength did not influence the content or time frame over which services were exchanged. SNA was found to provide useful measures for quantifying the structure of female Assamese macaques social relationships and to provide other potentially useful measures for future studies of non-human social relationships. These results provide a valuable contribution to our understanding of both non-human and human social relationships. They provide us with a fuller picture of the social lives of Assamese macaques in general, showing that strong, social relationships are an important feature of female social lives in this species, while dominance rank plays a relatively limited role in female behaviour. They also provide further support for the “valuable” relationship approach to understanding non-human social relationships, as opposed to the biological market approach suggested by some. Lastly, by providing further evidence that social relationships among nonhuman species share important characteristics with strong human social relationships these results also have implications for our understanding of the evolutionary origins of human social relationships, particularly the original functional benefits these relationships evolved to provide. In the future, we can further deepen our understanding of non-human social relationships by continuing to investigate which characteristics these relationships share with strong human social relationships. At the same time, we should also attempt to identify and investigate characteristics of social relationships which may be more meaningful specifically for non-human species. Lastly, we should begin to turn our attention to the many weak and dynamic social relationships that exist in groups of non-human species and the potential benefits that they may provide.