Understanding Animal Group-Size Distributions

Abstract

One of the most striking aspects of animal groups is their remarkable variation in size, both within and between species. While a number of mechanistic models have been proposed to explain this variation, there are few comprehensive datasets against which these models have been tested. In particular, we only vaguely understand how environmental factors and behavioral activities affect group-size distributions. Here we use observations of House sparrows (Passer domesticus) to investigate the factors determining group-size distribution. Over a wide range of conditions, we observed that animal group sizes followed a single parameter distribution known as the logarithmic distribution. This single parameter is the mean group size experienced by a randomly chosen individual (including the individual itself). For sparrows, the experienced mean group size, and hence the distribution, was affected by four factors: morning temperature, place, behavior and the degree of food spillage. Our results further indicate that the sparrows regulate the mean group size they experience, either by groups splitting more or merging less when local densities are high. We suggest that the mean experienced group size provides a simple but general tool for assessing the ecology and evolution of grouping.

Published in

PLoS ONE
2011, volume: 6, number: 8, article number: e23438
Publisher: PUBLIC LIBRARY SCIENCE

SLU Authors

• Griesser, Michael

  • Department of Ecology, Swedish University of Agricultural Sciences
    
  • University of Bern
  • Uppsala University

UKÄ Subject classification

Behavioral Sciences Biology
Environmental Sciences
Probability Theory and Statistics

Publication identifier

• DOI: https://doi.org/10.1371/journal.pone.0023438

Permanent link to this page (URI)

https://res.slu.se/id/publ/58849