Behavioral Ecology and Sociobiology

, Volume 1, Issue 4, pp 383–404 | Cite as

Social organization and foraging in emballonurid bats

II. A model for the determination of group size
  • J. W. Bradbury
  • S. L. Vehrencamp


  1. 1.

    Graphical methods are presented for the simultaneous comparisons of group size and territory size (subsumed jointly under the term “social dispersion”), in organisms with exclusive but contiguous territories. The methods are applied to recently published data on five species of neotropical emballonurid bats with particular emphasis on identifying the factors which set maximal limits on group size. The available evidence suggests that population densities, group territory sizes, and group sizes are all limited by components of the food distribution. More particularly, it is argued that minimization of annual foraging ranges is of advantage to these bats and leads to a colony territory size containing one and only one active food site at any given time. Territory size is thus determined by the average distance between successively available food sites, the number of such sites needed per year, and the average size of these sites. Maximal group size is then determined as a result of this territory size minimization and equals average richness of currently used food patches.

  2. 2.

    The model predicts that where food patches are low in richness and close together, social dispersion will be fine-grained; where patches are high in richness and occur far apart, social dispersion will be coarse-grained. Since sites in this study which have many small patches tend to be located in the more stable habitats, the model also predicts that temporal stability in group size and unimodal frequency distributions of group size over space will be associated with fine-grained dispersions. The reverse is predicted for coarse-grained social dispersions.

  3. 3.

    The model only predicts the maximal size colonies can take. Among the many possible factors promoting social aggregation up to the predicted maxima, only a few account for the observed congruence in colony sizes and compositions at the roost and on the foraging grounds. These include information transfer about new food sites, location of roosts centrally to reduce energy costs of transit (Horn, 1968), and stabilization of competition with conspecifics at food sites.



Group Size Colony Size Food Patch Territory Size Active Food 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag 1976

Authors and Affiliations

  • J. W. Bradbury
    • 1
  • S. L. Vehrencamp
    • 1
  1. 1.Department of BiologyUniversity of California at San DiegoLa JollaUSA

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