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The interpretation of tests for ratio-dependence

Ruxton, G.D. and Gurney, William (1992) The interpretation of tests for ratio-dependence. Oikos, 65 (2). pp. 334-335.

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Abstract

A number of recent publications have suggested that unstructured consumer-food models, in which the consumer functional response is regarded as a function of the ratio of food and consumer densities, may provide a better guide to the behaviour of natural systems than models in which the functional response is seen as density-independent. Recently, Arditi et al. (1991; Oikos 60: 69-75), have described a series of experiments, which are claimed to demonstrate such ratio-dependence in the functional response of two species of cladocerans. In this letter we re-examine the theory underlying these experiments, and show that although they form a powerful test for density-dependence in the functional response, they do not distinguish ratio-dependence from other equally plausible forms of density dependence. We conclude that the results of Arditi et al.'s experiments may be more effectively interpreted in terms of the density dependent functional response first proposed by J. R. Beddington, and discuss how such experiments might be used to further elucidate the behavioural mechanisms underlying observed density-dependence.