The Allometric Scaling of Density and Body Mass: A Nonlinear Relationship for Terrestrial Mammals

Predictions made by previous allometric analyses of the relationship between population density and body mass were tested using data on ecological density of 987 terrestrial mammal populations. The relationship is not log-log linear as previously postulated. Only populations of mammals with body mass between 0.1 and 100 kg had allometric exponents approaching the value of -0.75 proposed by previous studies. Different trophic groups showed divergent relationships between density and body mass. Previous global analyses have disagreed with relationships between density and body mass in individual communities partly because of this nonlinearity. Analyses of 45 mammalian communities show positive, negative, or even no relationship between density and body mass, depending on the trophic groups and body sizes of community members and the range of sizes. Population energy use is inequitably partitioned among populations, with populations of large mammals using more than 100 times more energy than the smallest mammals. Herbivorous mammals can use 25 times the energy used by carnivores, and populations of small insectivores use only 10% of the energy used by other carnivores of equivalent body mass.