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 dependence of production and mortality rates differ between species of the same taxon and that natural selection has optimized body size through optimal allocation of resources to growth and reproduction independently in each species. In a simple simulation model, we obtain good interspecific allometries for respiration, assimilation, production rates, age at maturity, and life expectancy. Some correlations, for example, those between age at maturity and life expectancy, remain significant after the effect of body size is removed. The slopes of the allometries depend not only on the average values of the parameters but also on their coefficients of variation. We show analytically how these slopes are determined for a simplifed model and how body size distributions are determined. In our model, interspecific allometries emerge as a result of body size optimization and the distributions of intraspecific production and mortality parameters.