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Competition on a Divided and Ephemeral Resource: Testing the Assumptions. II. Association

B. Shorrocks, J. Rosewell and K. Edwards
Journal of Animal Ecology
Vol. 59, No. 3 (Oct., 1990), pp. 1003-1017
DOI: 10.2307/5027
Stable URL: http://www.jstor.org/stable/5027
Page Count: 15
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Competition on a Divided and Ephemeral Resource: Testing the Assumptions. II. Association
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Abstract

(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 chi2 statistic. As a convenient index of association we use the four-point correlation coefficient [Note: equation omitted. See the image of page 1003 for this equation.] where N is the number of observations (patches) in the corresponding contingency table and chi2 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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