A method for testing association patterns of social animals

Association indices were originally developed to describe species co-occurrences, but have been used increasingly to measure associations between individuals. However, no statistical method has been published that allows one to test the extent to which the observed association index values differ from those of a randomly associating population. Here, we describe an adaptation of a test developed by Manly (1995, Ecology, 76, 1109-1115), which uses the observed association data as a basis for a computer-generated randomization. The observed pattern of association is tested against a randomly created one while retaining important features of the original data, for example group size and sighting frequency. We applied this new method to test four data sets of associations from two populations of Hector's dolphin, Cephalorhynchus hectori, using the Half-Weight Index (HWI) as an example of a measure of association. The test demonstrated that populations with similar median HWI values showed clear differences in association patterns, that is, some were associating nonrandomly whereas others were not. These results highlight the benefits of using this new testing method in order to validate the analysis of association indices. Copyright 1998 The Association for the Study of Animal Behaviour.

[1]  Steven J. Schwager,et al.  A comparison of association indices , 1987, Animal Behaviour.

[2]  M. Weinrich.  Stable social associations among humpback whales (Megaptera novaeangliae) in the southern Gulf of Maine , 1991 .

[3]  Lee Douglas Sailer,et al.  Proximity, Sociality, and Observation: The Definition of Social Groups , 1984 .

[4]  N. Metcalfe.  Variation in winter flocking associations and dispersion patterns in the turnstone Arenaria interpres , 1986 .

[5]  Randall S. Wells,et al.  The Social Structure of Free-Ranging Bottlenose Dolphins , 1987 .

[6]  Bryan F. J. Manly,et al.  A Note on the Analysis of Species Co‐Occurrences , 1995 .

[7]  H. Whitehead.  Analysing animal social structure , 1997, Animal Behaviour.

[8]  Truman P. Young,et al.  Measuring association between individuals or groups in behavioural studies , 1992, Animal Behaviour.

[9]  B. Würsig,et al.  Association Patterns of Bottlenose Dolphins (Tursiops truncatus) in Galveston Bay, Texas , 1994 .

[10]  J. Mitani,et al.  Association among wild orang-utans: sociality, passive aggregations or chance? , 1991, Animal Behaviour.

[11]  The migration of humpback whales along the northeast coast of Newfoundland , 1982 .

[12]  V. Gelder,et al.  The Serengeti Lion , 1973 .

[13]  R. Underwood.  Companion preference in an eland herd , 1981 .

[14]  Associations among photographically identified Hector's dolphins , 1993 .

[15]  Z. Hubálek.  COEFFICIENTS OF ASSOCIATION AND SIMILARITY, BASED ON BINARY (PRESENCE‐ABSENCE) DATA: AN EVALUATION , 1982 .

[16]  L. R. Dice.  Measures of the Amount of Ecologic Association Between Species , 1945 .

[17]  John W. Pepper,et al.  Sex Differences in Patterns of Association Among Indian Ocean Bottlenose Dolphins , 1992 .

[18]  Bernd Würsig,et al.  The Photographic Determination of Group Size, Composition, and Stability of Coastal Porpoises (Tursiops truncatus) , 1977 .