INTERSPECIFIC ALLOMETRIES ARE BY-PRODUCTS OF BODY-SIZE OPTIMIZATION

Many physiological and life-history traits correlate with body weight in interspecific comparisons. To explain these allometries, we assume that the parameters of within-species functions describing the size de pendence of production and mortality rates differ between species of t he same taxon and that natural selection has optimized body size throu gh optimal allocation of resources to growth and reproduction independ ently in each species. In a simple simulation model, we obtain good in terspecific allometries for respiration, assimilation, production rate s, age at maturity, and life expectancy. Some correlations, for exampl e, those between age at maturity and life expectancy, remain significa nt after the effect of body size is removed. The slopes of the allomet ries depend not only on the average values of the parameters but also on their coefficients of variation. We show analytically how these slo pes are determined for a simplifed model and how body size distributio ns are determined. In our model, interspecific allometries emerge as a result of body size optimization and the distributions of intraspecif ic production and mortality parameters.