Shorrocks, Bryan; Rosewell, Jonathan and Edwards, Kathy
Competition on a divided and ephemeral resource: Testing the Assumptions. II. Association.
Journal of Animal Ecology, 59(3) pp. 1003–1017.
(1) We test the assumption of the aggregation model of coexistence on a divided and ephemeral resource that there is no association between species.
(2) We test associations by presence and absence from patches using 2 x 2 contingency tables and the chi-squared statistic. As a convenient index of association we use the four-point correlation coefficient phi = sqrt(chi-squared/N) where N is the number of observations (patches) in the corresponding contingency table and chi-squared is the uncorrected statistic.
(3) The data, from laboratory experiments, field experiments and field collections shows no evidence of association between species pairs. Out of 157 comparisons, only eight show significant associations at the 5% level.
(4) We incorporate phi into the original aggregation model for two-species competition and into the guild-size extension and examine its influence. Probability refuges and resource refuges are therefore brought together within one conceptual framework.
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