Background/Question/Methods Dramatic regularities in the scaling of body mass and energetics across the huge range of mammal sizes suggest the existence of fundamental scaling laws in animal body size.  However, these laws are apparently independent of environmental conditions because a large range of body size is found in most mammal assemblages.  At the level of intraspecific body size variation, there is some evidence for latitudinal patterns related to the thermodynamics of energy loss, as expressed in Bergmann’s rule for temperature effects on body size.  We note that there are both longitudinal, as well as latitudinal, variations in mammal body size that are independent of temperature.

Results/Conclusions Our analysis of spatial variation in body size in raccoons, white-tailed deer, and humans suggests that it is food availability, as regulated by net primary productivity, that best explains the variation in body size within these species.  We find strong relationships of both soil nutrient content and estimated eNPP (monthly average NPP during the growing season) with body size, which suggests that intraspecific variation in mammal body size can be used as a correlate for both net secondary production and net primary production, specifically eNPP.  Latitudinal patterns of intraspecific body size variation in these and other species are consistent with the interpretation that eNPP is higher in the temperate zone than in most of the tropics.