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

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.

Methods
The submitted data are Association Distance Matrices of adult, free ranging female African elephants inhabiting the Samburu ecosystem of northern Kenya. Association distance was calculated as 1 - Association Index (AI) values, where the simple ratio index is used to calculate AI Values using association data collected by registering all elephants encountered along four established reserve transects (date, time, GPS coordinates, group size, individuals present, and observation accuracy were recorded). Elephants were considered to be associating when behaviorally coordinated and spatially cohesive within 500m of an observer-estimated center. Only observation where the observer was completely certain of identifying all individuals in the group. For more details see:

WITTEMYER, G., Douglas-Hamilton, I., & Getz, W.M. 2005. The socio-ecology of   elephants: Analysis of the processes creating multileveled societies. *Animal Behaviour* 69:1357-1371
Goldenberg, S. Z.*, Douglas-Hamilton, I., WITTEMYER, G. 2016*. Vertical transmission of social roles drives resilience to poaching in elephant networks. *Current Biology* 26:75-79