Abstract
For species in which group membership frequently changes, it has been a challenge to characterize variation in individual interactions and social structure. Quantifying this variation is necessary to test hypotheses about ecological determinants of social patterns and to make predictions about how group dynamics affect the development of cooperative relationships and transmission processes. Network models have recently become popular for analyzing individual contacts within a population context. We use network metrics to compare populations of Grevy’s zebra (Equus grevyi) and onagers (Equus hemionus khur). These closely related equids, previously described as having the same social system, inhabit environments differing in the distribution of food, water, and predators. Grevy’s zebra and onagers are one example of many sets of coarsely similar fission–fusion species and populations, observed elsewhere in other ungulates, primates, and cetaceans. Our analysis of the population association networks reveals contrasts consistent with their distinctive environments. Grevy’s zebra individuals are more selective in their association choices. Grevy’s zebra form stable cliques, while onager associations are more fluid. We find evidence that females associate assortatively by reproductive state in Grevy’s zebra but not in onagers. The current approach demonstrates the utility of network metrics for identifying fine-grained variation among individuals and populations in association patterns. From our analysis, we can make testable predictions about behavioral mechanisms underlying social structure and its effects on transmission processes.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Altizer S et al. (2003) Social organization and parasite risk in mammals: integrating theory and empirical studies. Annu Rev Ecol Evol Syst 34:517–547
Altmann J et al. (1996) Behavior predicts genetic structure in a wild primate group. Proc Natl Acad Sci USA 93:5797–5801
Bejder L, Fletcher D, Brager S (1998) A method for testing association patterns of social animals. Anim Behav 56:719–725
Bonabeau E, Dagorn L, Freon P (1999) Scaling in animal group-size distributions. Proc Natl Acad Sci USA 96:4472–4477
Borgatti SP, Everett MG, Freeman LC (2002) UCINET for Windows: software for social network analysis. Analytic Technologies, Harvard, MA
Brager S (1999) Association patterns in three populations of Hector’s dolphin, Cephalorhynchus hectori. Can J Zool 77:13–18
Cairns SJ, Schwager SJ (1987) A comparison of association indexes. Anim Behav 35:1454–1469
Chapman CA, White FJ, Wrangham RW (1993) Defining subgroup size in fission–fusion societies. Folia Primatol 61:31–34
Couzin ID, Krause J (2003) Self-organization and collective behavior in vertebrates. Adv Study Behav 32:1–75
Croft DP, Krause J, James R (2004) Social networks in the guppy (Poecilia reticulata). Proc R Soc Lond B Biol Sci 271:S516–S519
Croft DP, James R, Ward AJW, Botham MS, Mawdsley D, Krause J (2005) Assortative interactions and social networks in fish. Oecologia 143:211–219
Cross PC, Lloyd-Smith JO, Getz WM (2005) Disentangling association patterns in fission–fusion societies using African buffalo as an example. Anim Behav 69:499–506
Feh C, Boldsukh T, Tourenq C (1994) Are family groups in equids a response to cooperative hunting by predators—the case of Mongolian Kulans (Equus hemionus luteus). Revue D Ecologie-La Terre Et La Vie 49:11–20
Galef BG, Laland KN (2005) Social learning in animals: empirical studies and theoretical models. Bioscience 55:489–499
Ginsberg JR (1987) Social organization and mating strategies of an arid adapted equid: the Grevy’s zebra. PhD Thesis. Princeton University, Princeton, USA, p 268
Ginsberg JR, Rubenstein DI (1990) Sperm competition and variation in zebra mating-behavior. Behav Ecol Sociobiol 26:427–434
Good P (2000) Permutation tests: a practical guide to resampling methods for testing hypotheses, 2nd edn. Springer, Berlin Heidelberg New York
Hemelrijk CK (1999) An individual-orientated model of the emergence of despotic and egalitarian societies. Proc R Soc Lond B Biol Sci 266:361–369
Hinde RA (1976) Interactions, relationships and social-structure. Man 11:1–17
Keeling MJ, Eames KTD (2005) Networks and epidemic models. J R Soc Interface 2:295–307
Klingel H (1998) Observations on social organization and behaviour of African and Asiatic Wild Asses (Equus africanus and Equus hemionus) (reprinted from Z Tierpsychol, vol 44, pp 323–331, 1977). Appl Anim Behav Sci 60:103–113
Krause J, Ruxton GD (2002) Living in groups. Oxford University Press, Oxford
Kudo H, Dunbar RIM (2001) Neocortex size and social network size in primates. Anim Behav 62:711–722
Lusseau D (2003) The emergent properties of a dolphin social network. Proc R Soc Lond B Biol Sci 270:S186–S188
Lusseau D, Newman MEJ (2004) Identifying the role that animals play in their social networks. Proc R Soc Lond B Biol Sci 271:S477–S481
Manly BFJ (1995) A note on the analysis of species cooccurrences. Ecology 76:1109–1115
McComb K, Moss C, Durant SM, Baker L, Sayialel S (2001) Matriarchs as repositories of social knowledge in African elephants. Science 292:491–494
Moehlman PD (2002) Equids: zebras, asses, and horses: status survey and conservation action plan. IUCN/SSC Equid Specialist Group, Gland, Switzerland
Newman MEJ (2003) The structure and function of complex networks. Siam Rev 45:167–256
Rubenstein DI (1986) Ecology and sociality in horses and zebras. In: Rubenstein DI, Wrangham RW (eds) Ecological aspects of social evolution: birds and mammals. Princeton University Press, Princeton, NJ, pp 282–302
Rubenstein DI (1994) Ecology of female social behavior in horses, zebras and asses. In: Jarman P, Rossiter A (eds) Animal societies: individuals, interaction and organisation. Kyoto University Press, Kyoto, pp 13–28
Rubenstein DI, Wrangham RW (1986) Ecological aspects of social evolution: birds and mammals, 1st edn. Princeton University Press, Princeton, NJ
Symington MM (1990) Fission–Fusion social-organization in Ateles and Pan. Int J Primatol 11:47–61
Wasserman S, Faust K (1994) Social network analysis. Cambridge University Press, Cambridge
Watts DJ, Strogatz SH (1998) Collective dynamics of ‘small-world’ networks. Nature 393:440–442
Whitehead H (1997) Analysing animal social structure. Anim Behav 53:1053–1067
Whitehead H, Dufault S (1999) Techniques for analyzing vertebrate social structure using identified individuals: review and recommendations. Adv Study Behav 28:33–74
Acknowledgments
We thank Gujarat Forest Department and Kenya Ministry of Education for permission to work in India and Kenya, respectively. Tanya Berger-Wolf, Stephen Pratt, Simon Levin, David Lusseau, Marc Mangel, and one anonymous reviewer gave us valuable comments on drafts of the manuscript. Patrick Akilong, Jayanti Degama, and Yaseen Malek provided field assistance. Mpala Research Center offered logistical field support. For financial support, we acknowledge Wildlife Conservation Society Research Fellowship Program (SRS), Teresa Heinz Environmental Scholars program (IRF), Pew Charitable Trusts award 2000-0002558 “Program in Biocomplexity” to Princeton University Department of Ecology and Evolutionary Biology (SRS, DIR, IRF), NSF grant CNS-025214 (DIR, IRF), NSF grant IOB-9874523 (DIR) and NSF grant IBN-0309233 (DIR, SRS). All research presented here complies with laws in Kenya, India, and the United State of America.
Author information
Authors and Affiliations
Corresponding author
Additional information
Communicated by Marc Mangel.
Rights and permissions
About this article
Cite this article
Sundaresan, S.R., Fischhoff, I.R., Dushoff, J. et al. Network metrics reveal differences in social organization between two fission–fusion species, Grevy’s zebra and onager . Oecologia 151, 140–149 (2007). https://doi.org/10.1007/s00442-006-0553-6
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00442-006-0553-6