, Volume 143, Issue 2, pp 211–219 | Cite as

Assortative interactions and social networks in fish

  • D. P. Croft
  • R. James
  • A. J. W. Ward
  • M. S. Botham
  • D. Mawdsley
  • J. Krause
Population Ecology


The mechanisms underpinning the structure of social networks in multiple fish populations were investigated. To our knowledge this is the first study to provide replication of social networks and therefore probably the first that allows general conclusions to be drawn. The social networks were all found to have a non-random structure and exhibited ‘social cliquishness’. A number of factors were observed to contribute to this structuring. Firstly, social network structure was influenced by body length and shoaling tendency, with individuals interacting more frequently with conspecifics of similar body length and shoaling tendency. Secondly, individuals with many social contacts were found to interact with each other more often than with other conspecifics, a phenomenon known as a ‘positive degree correlation’. Finally, repeated interactions between pairs of individuals occurred within the networks more often than expected by random interactions. The observed network structures will have ecological and evolutionary implications. For example, the occurrence of positive degree correlations suggests the possibility that pathogens and information (that are socially transmitted) could spread very fast within the populations. Furthermore, the occurrence of repeated interactions between pairs of individuals fulfils an important pre-requisite for the evolution of reciprocal altruism.


Guppies Sticklebacks Group living Social organisation 



We would like to thank Bethany Arrowsmith and Michael Webster for their assistance in collecting the data in the field and Christina Prell for advice on social network analysis. We would also like to thank Ronnie Hernandez and the board of Asa Wright Nature Centre, Trinidad, for their continued support and assistance in the field. D.P.Croft would like to acknowledge funding from the Frank Parkinson scholarship (University of Leeds), FSBI and the Leverhulme trust.


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Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  • D. P. Croft
    • 1
  • R. James
    • 2
  • A. J. W. Ward
    • 3
  • M. S. Botham
    • 1
  • D. Mawdsley
    • 2
  • J. Krause
    • 1
  1. 1.School of BiologyUniversity of LeedsLeedsUK
  2. 2.Department of PhysicsUniversity of BathBathUK
  3. 3.Department of BiologyUniversity of LeicesterLeicesterUK

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