The socioecology of elephants: analysis of the processes creating multitiered social structures

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2004.08.018 Byline: G. Wittemyer, I. Douglas-Hamilton, W.M. Getz Abstract: In this paper, we investigate the formation and function of the multilevelled, fission-fusion social structure in a free-ranging African elephant, Loxodonta africana, population. We quantitatively identified the existence of four social tiers by using cluster analysis on individual association data. We assessed the effects of season and study period on social structuring and levels of cohesion within and among social units. We found that second-tier units, potentially the equivalent of the 'family', were stable across seasonal periods but the number of units increased as the study progressed and the population grew. It appears that these units were sufficiently small not to be influenced by ecologically related factors, such as resource competition, that might otherwise lead to them splitting. On the other hand, third- and fourth-tier units were significantly affected by season in a way that suggests a trade-off between ecological costs (e.g. from resource competition) and different social and ecological benefits (e.g. from predator defence, territoriality, knowledge sharing and rearing of young). Age structure also appeared to influence this multitiered social organization. The size of second-tier social units was significantly affected by the age of matriarchs: units lead by matriarchs likely to be grandmothers (i.e. females 35 years and older) were significantly larger than those lead by younger matriarchs. We present a conceptual framework for understanding the emergence of multiple-tier social structure from interactions driven by socioecological processes. This study is the first to use rigorous quantitative methods to statistically show the existence of four hierarchical tiers of social organization in a nonhuman animal. Additionally, our results elucidate the role that ecological processes play in producing complex social structures. Author Affiliation: (*) Department of Environmental Science, Policy and Management, University of California, Berkeley, U.S.A. (a ) Save the Elephants, Kenya (a ) Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, South Africa Article History: Received 17 June 2004; Revised 23 July 2004; Accepted 18 August 2004 Article Note: (miscellaneous) MS. number: A9821