On Being the Right Size

Abstract

Most examinations of body size center on a single factor. However, because body size is directly or indirectly linked to many, if not most, life history characters a more holistic approach is advocated. In this paper I present such an approach in the analysis of the optimum body size of Drosophila melanogaster. The basic life history parameters determining r are shown to be related to body size. Using these functions the relationship between r and body size is obtained. It is found that r is maximized within the observed range in size. A sensitivity analysis indicates that this result does not depend critically upon parameter estimation. This analysis also indicates that variation in egg size between geographic strains should be positively correlated to variation in body size. This prediction is shown to be correct. Reasonable variation in parameter values can account for much of the size range observed in the genus Drosophila. It does not appear to be possible to account for the very large size of certain Hawaiian species.