Abstract
The goal of our presentation is to provide more comparative evidence for social organization of Japanese macaques in various habitats and to emphasize variation and plasticity of their social systems. Recent studies indicate considerable species differences in inter-individual tolerance in species of the genus Macaca. Japanese macaque is considered 'despotic' species that exhibit showing less tolerance, less affiliation, greater inter-individual distances, and more severe and asymmetrical patterns of aggression. These despotic characteristics contrast those of tolerant species as stumptail macaque, tonkean macaques, tibetan macaques and bonnet macaques. Such inter-specific differences however are difficult to test in the field because adequate comparative data are lacking on wild populations, and studies have been largely limited to captive groups or experimental situations.
The social organization of Japanese macaque varies within the range of their habitats. Several pioneer researchers (e.g. Yamada M and Koyama N) reported that behavior patterns of the monkeys on Shodoshima differed from those of other populations of Japanese macaques. These differences included highly tolerant inter-individual interactions, close inter-individual distances, and crowded feeding within a narrow space. In other populations, 'Youngest ascendancy' that has been documented in many provisioned populations was absent in Takasakiyama and a wild population in Yakushima. Inter-group comparisons suggest that the social structure of Japanese macaques might be highly plastic. However, documentation of intra-specific variation are need to apply more comparative approaches involving several groups per type of environments, and long-term data collected using standardized methodology.
We conducted a study on dominance style of three free-ranging groups: SB group on Shodoshima Island (west Japan), TC group in Takasakiyama (west Japan) and JA1 group at Jigokudani (north-central Japan). Standard data on aggressive and affiliative behaviour were collected over a period of five years from 2004 to 2009. We used focal animal sampling to collect data regarding intragroup interactions among members of study groups. We randomly selected 16 focal subjects (seven adult males and nine adult females) in each study group, and recorded all instances of social behavior in 30 30-min sessions for each focal subject during non-feeding time. With focal sample data, we calculated and compared behavior following behavior measures: approach frequency, grooming duration, hourly rates for aggression, intensity of aggressions (percentages of threat, attach and fierce bite) and symmetry of aggression. Compared with Japanese macaques at Takasakiyama and Jigokudani, those in Shodoshima show: more frequent affinitive interactions, shorter inter-individual distance, more frequent ignoring of exclusion, more frequent aggression, less intense aggression, and more frequent counter-aggression. These characteristics suggest that the Japanese macaques on Shodoshima have relaxed dominant relations. In this study, we attempt to analysis social relations of Japanese macaques in a comparative framework by using the standardized behavioral measurements as those of studies on captive populations. We realize difference study situation between the free-ranging populations and captive populations, such as group size is very large and individual identification are difficult in this study, yet this study is to provide more comparative evidence for social organization of Japanese macaques in various habitats. In the hope and expectation that others will help the volume of comparative data in various habitats to grow, this type of research may contribute an overall picture of social organization within the genus macaque that include both intra-and inter-species variation.
