Behavioral Ecology and Sociobiology

, Volume 62, Issue 12, pp 1863–1868 | Cite as

Within-group spatial position and vigilance: a role also for competition? The case of impalas (Aepyceros melampus) with a controlled food supply

  • Pierrick BlanchardEmail author
  • Rodolphe Sabatier
  • Hervé Fritz
Original Paper


Theory predicts that individuals at the periphery of a group should be at higher risk than their more central conspecifics since they would be the first to be encountered by an approaching terrestrial predator. As a result, it is expected that peripheral individuals display higher vigilance levels. However, the role of conspecifics in this “edge effect” may have been previously overlooked, and taking into account the possible role of within-group competition is needed. Vigilance behavior in relation to within-group spatial position was studied in impalas (Aepyceros melampus) feeding on standardized patches. We also controlled for food distribution in order to accurately define a “central” as opposed to a “peripheral” position. Our data clearly supported an edge effect, with peripheral individuals spending more time vigilant than their central conspecifics. Data on social interactions suggest that it was easier for a foraging individual to defend its feeding patch with its head lowered, and that more interactions occurred at the center of the group. Together, these results indicate that central foragers may reduce their vigilance rates in response to increased competition. Disentangling how the effects of competition and predation risk contribute to the edge effect requires further investigations.


Vigilance Food control Edge effect Predation Competition 



We are grateful to C. Bonenfant, S. Devillard, J.-M. Gaillard, M. Garel, M. Guillemain, M. Hewison, J. O’Brien and three anonymous referees for comments on an earlier draft. This project was developed within the HERD Project (CIRAD/CNRS). We are grateful to Zimbabwe Parks and Wildlife Management Authority for their support, and to the CNRS-NRF PICS program “Plant-herbivore dynamics in changing environments - developing appropriate models for adaptive management” for funding. Many thanks also to S. Le Bel (CIRAD-Zimbabwe) for facilitating the operations. We are also grateful to all the kids from Main Camp for their joyful support and pods collection, and we thank all the inhabitants of Main Camp for their understanding and tolerance as they adapted their routes during the observation sessions.


  1. Arenz CL, Leger DW (1999) Thirteen-lined ground squirrel (Sciuridae: Spermophilus tridecemlineatus) antipredator vigilance decreases as vigilance cost increases. Anim Behav 57:97–103PubMedCrossRefGoogle Scholar
  2. Balmford A, Turyaho M (1992) Predation risk and lek-breeding in Uganda kob. Anim Behav 44:117–127CrossRefGoogle Scholar
  3. Beauchamp G (2003) Group-size effects on vigilance: a search for mechanisms. Behav Proc 63:111–121CrossRefGoogle Scholar
  4. Berger J (1991) Pregnancy incentives, predation constraints and habitat shifts: experimental and field evidence for wild bighorn sheep. Anim Behav 41:61–77CrossRefGoogle Scholar
  5. Berger J, Cunningham C (1988) Size-related effects on search times in North American grassland female ungulates. Ecology 69:177–183CrossRefGoogle Scholar
  6. Blumstein DT, Daniel JC (2003) Red kangaroos (Macropus rufus) receive an antipredator benefit from aggregation. Acta Ethol 5:95–99CrossRefGoogle Scholar
  7. Blumstein DT, Daniel JC, Ardron JG, Evans CS (2002) Does feeding competition influence tammar wallaby time allocation? Ethology 108:937–945CrossRefGoogle Scholar
  8. Burger J, Gochfeld M (1994) Vigilance in African mammals: differences among mothers, other females, and males. Behaviour 131:153–169CrossRefGoogle Scholar
  9. Burger J, Safina C, Gochfeld M (2000) Factors affecting vigilance in springbok: importance of vegetative cover, location in herd, and herd size. Acta Ethol 2:97–104CrossRefGoogle Scholar
  10. Clark CW, Mangel M (1986) The evolutionary advantages of group foraging. Theor Pop Biol 30:45–75CrossRefGoogle Scholar
  11. Elgar MA (1989) Predator vigilance and group size in mammals and birds: a critical review of the empirical evidence. Biol Rev 64:13–33PubMedCrossRefGoogle Scholar
  12. Fernández-Juricic E, Beauchamp G, Bastain B (2007) Group-size and distance-to-neighbour effects on feeding and vigilance in brown-headed cowbirds. Anim Behav 73:771–778CrossRefGoogle Scholar
  13. Fortin D, Boyce MS, Merrill EH, Fryxell JM (2004) Foraging costs of vigilance in large mammalian herbivores. Oikos 107:172–180CrossRefGoogle Scholar
  14. Frid A (1997) Vigilance by female Dall's sheep: interactions between predation risk factors. Anim Behav 53:799–808CrossRefGoogle Scholar
  15. Hamilton WD (1971) Geometry of the selfish herd. J Theor Biol 31:295–311PubMedCrossRefGoogle Scholar
  16. Hirsch BT (2007) Costs and benefits of within-group spatial position: a feeding competition model. Quart Rev Biol 82:9–27PubMedCrossRefGoogle Scholar
  17. Inglis IR, Lazarus J (1981) Vigilance and flock size in brent geese: the edge effect. Z Tierpsychol 57:193–200Google Scholar
  18. Jennings T, Evans SM (1980) Influence of position in the flock and flock size on vigilance in the starling Sturnus vulgaris. Anim Behav 28:634–635CrossRefGoogle Scholar
  19. Krause J (1994) Differential fitness returns in relation to spatial position in groups. Biol Rev 69:187–206PubMedCrossRefGoogle Scholar
  20. Lingle S (2001) Anti-predator strategies and grouping patterns in white-tailed deer and mule deer. Ethology 107:295–314CrossRefGoogle Scholar
  21. Mooring MS, Fitzpatrick TA, Nishihira TT, Reisig DD (2004) Vigilance, predation risk, and the Allee effect in desert Bighorn Sheep. J Wildl Manage 68:519–532CrossRefGoogle Scholar
  22. Pinheiro JC, Bates DM (2000) Mixed-effects models in S and S-PLUS, Springer, New YorkGoogle Scholar
  23. Proctor CJ, Broom M, Ruxton GD (2006) Antipredator vigilance in birds: modelling the “edge” effect. Math Biosc 199:76–96CrossRefGoogle Scholar
  24. Pulliam HR (1973) On the advantages of flocking. J Theor Biol 38:419–422PubMedCrossRefGoogle Scholar
  25. R Development Core Team (2005) R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. ISBN 3-900051-07-0. URL
  26. Ron T, Henzi SP, Motro U (1996) Do female chacma baboons compete for a safe spatial position in a southern woodland habitat? Behaviour 133:475–490CrossRefGoogle Scholar
  27. Stankowich T (2003) Marginal predation methodologies and the importance of predator preferences. Anim Behav 66:589–599CrossRefGoogle Scholar
  28. Underwood R (1982) Vigilance behaviour in grazing African antelopes. Behaviour 79:81–107CrossRefGoogle Scholar
  29. Zwarts L (1976) Density-related processes in feeding dispersion and feeding activity of Teal (Anas crecca). Ardea 64:192–209Google Scholar

Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • Pierrick Blanchard
    • 1
    Email author
  • Rodolphe Sabatier
    • 2
  • Hervé Fritz
    • 2
  1. 1.Université de Lyon; université Lyon 1—CNRS UMR 5558Laboratoire de Biométrie et Biologie Evolutive 43VilleurbanneFrance
  2. 2.Centre d’Études Biologiques de Chizé, CNRSVilliers en BoisFrance

Personalised recommendations