Abstract
Asian and African elephant species have diverged by ca. 6 million years, but as large, generalist herbivores they occupy similar niches in their respective environments. Although the multilevel, hierarchical nature of African savannah elephant societies is well established, it has been unclear whether Asian elephants behave similarly. Here we quantitatively compare the structure of both species’ societies using association data collected using the same protocol over similar time periods. Sociality in both species demonstrates well-defined structure, but in contrast to the African elephants of Samburu the Uda Walawe Asian elephants are found in smaller groups, do not maintain coherent core groups, demonstrate markedly less social connectivity at the population level, and are socially less influenced by seasonal differences in ecological conditions. The Uda Walawe Asian elephants, however, do maintain a complex, well-networked society consisting of ≥2 differentiated types of associates we term ephemeral and long-term affiliates. These findings imply we must broaden our recognition of multilevel social organization to encompass societies that fall along a gradient of nestedness, and not merely those that exhibit hierarchical nesting. This in turn suggests that multilevel structures may be more diverse and widespread than generally thought, and that phylogenetic comparisons within species-rich clades, such as that of primates, using the methods presented can provide fresh insights into their socioecological basis.






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Acknowledgments
S. de Silva was partially supported by funding from the Binns-Williams Fund in the University of Pennsylvania graduate group in Ecology and Evolution, a Doctoral Dissertation Completion grant from the University of Pennsylvania, an Integrative Graduate Education and Research Traineeship grant from National Science Foundation (NSF-IGERT 0504487), and a grant from the U.S. Fish & Wildlife Asian Elephant Conservation Fund (grant no. 98210-7-G167). We thank 2 anonymous reviewers and guest editor C. C. Grueter for their constructive comments on the manuscript.
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de Silva, S., Wittemyer, G. A Comparison of Social Organization in Asian Elephants and African Savannah Elephants. Int J Primatol 33, 1125–1141 (2012). https://doi.org/10.1007/s10764-011-9564-1
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DOI: https://doi.org/10.1007/s10764-011-9564-1