ASSEMBLY OF LOCAL-COMMUNITIES - CONSEQUENCES OF AN OPTIMAL BODY-SIZE FOR THE ORGANIZATION OF COMPETITIVELY STRUCTURED COMMUNITIES

Much empirical evidence suggests that there is an optimal body size fo r mammals and that this optimum is in the vicinity of 100 g. This pres umably reflects an underlying fitness function that is greatest at thi s mass. Here, I combine such a fitness function with an equilibrium mo del of competitive character displacement to assess the potential infl uence of a globally optimal body size in structuring local ecological communities. The model accurately predicts the range of body sizes and the average difference in size for species in communities of varying species richness. The model also predicts a uniform spacing of body si zes, rather than the gaps and clumps in the sizes of coexisting specie s observed in real communities. Alternative explanations for this phen omenon are discussed. The allometric relationships that result in a bo dy size optimum subsume a large number of characteristics associated w ith the physiological, behavioral, demographic, and evolutionary dynam ics of the species. Further integration of the underlying dynamics (e. g. individual energetics) of these relationships into all hierarchical levels of ecology will have to incorporate multiple interactive sites , spatial heterogeneity, and phylogenetic structure, but it has the po tential to provide important discoveries into the means by which natur al selection operates.