Optimal Habitat Selection in Time-Limited Dispersers

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. The life cycles of a wide variety of organisms include a dispersal phase that precedes reproduction. The main function of this stage is to select an appropriate habitat for reproduction and the development of offspring. Several models of optimal habitat selection have assumed that the optimal behavior results in an "ideal free distribution," in which no individual could increase its fitness by being elsewhere (e.g., Fretwell and Lucas 1970;Fretwell 1972). In species whose dispersal stage is brief or marked by heavy mortality, however, the benefits of rejecting suboptimal habitats may be outweighed by the cost of failing to find a habitat at all. The University of Chicago Press andModels of time-limited habitat selection have been presented by Levins (1968), Levins and MacArthur (1969), Jaenike (1978), andCourtney (1982). Specificity (i.e., rejection of suboptimal habitats) is favored if optimal habitats are abundant, if a long time is available for the search, or if fitness in inferior habitats is low. A related model has been used to explain the high incidence of polyphagy among aphids inhabiting areas of high floral diversity, since this is associated with relatively low densities of each plant species (Dixon et al. 1987). Finally, Doyle (1979) has shown that in species with a constant instantaneous mortality rate during dispersal, an initial "exploratory phase" may be adaptive if the abundance of optimal sites is unpredictable.I consider here the evolution of habitat-acceptance behavior in a time-limited disperser. This behavior is expressed as the probability that a habitat of a particular type is accepted (i.e., that the dispersing organism settles, rather than searching further) once it has been encountered. The model includes the possibility that the probability of acceptance varies during the course of the dispersal phase. In addition, since the total time available is held constant, the expected future time available declines. (This is often more realistic than the frequent assumption of constant mortality in, e.g., nonfeeding dispersers.) These assumptions are similar to those on which Jaenike (1978) based his model, except that in his inequality (1) it is implicitly assumed that if a host plant (i.e., {habitat) of a particular type is rejected, no further hosts of this type will be encountered (or, if encountered, they

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