The Assessment of Preference

How to analyse prey preference when prey density varies? A new method to discriminate between effects of gut fullness and prey type composition

“…One approach is to assess how dietary composition changes with relative density of each prey type and/or total prey density in the environment. This requires a well defined measure of preference, the desirable properties of which are discussed at length by Cock (1978) and Lechowicz (1982). This measure should not itself change with prey density (nor with prey depletion) and it should vary only as a consequence of behavioural changes of the predator (apart from behavioural changes of the prey, a possibility which cannot be ruled out without additional observations).…”

“…Thus, the approach is in fact to test the null hypothesis that predator and prey do not change their behaviour as a result of the prey types being presented together. It was independently proposed by Rabbinge (1976) with much inspiration coming from De Wit's analysis of competition between plants by use of replacement series (De Wit 1963;De Wit and Goudriaan 1978) and Cock (1978) who modified a descriptive method proposed by Lawton et al (1974) into a predictive method. Examples can be found in De Wit and Goudriaan (1978), who used De Wit's yield equation (valid only under conditions of constant prey density), Akre and Johnson (1979) who used Holling's disc equation (under the same condition as the former), and Cock (1978), Fernando and Hassell (1980) and Colton (1987), who used Rogers' variant of the Holling disc equation (valid also under condi-tions of prey depletion).…”

“…The acarine predator-prey system concerns predatory mites (Acarina: Phytoseiidae) and various stages of development of a phytophagous prey mite (Acarina: Tetranychidae). It is chosen because there is convincing evidence that satiation is an important determinant of the attack rate (Sabelis 1981(Sabelis , 1985(Sabelis , 1986, and because previous attempts at analyzing prey-stage preference resulted in rejection of a two-prey version of Hotling's disc equation (or rather Rogers' variant of it) (Cock 1978;Fernando and Hassell 1980).…”

“…apple rust mites and (larvae of) European red spider mites. The underlying causes are to be revealed by further research, the impetus of which is born out by use of the method proposed by Cock (1978) and extended in this paper.…”

“…An interesting question is whether satiation alone is the determinant of the attack rate or whether the particular mixture of prey types in the predator's direct environment has an additional influence by itself. To detect examples of the latter type the predictive method proposed by Cock (1978) may be useful. In the present paper the predictive tool is a model built on the assumption that gut fullness is the sole internal state variable determining the attack rate.…”