BODY-SIZE, POPULATION-DENSITY, AND THE ENERGETIC EQUIVALENCE RULE

1. We critically evaluated the Energetic Equivalence Rule (EER) with r egard to its underlying theoretical framework, its dependence of a par ticular relationship between population density and body size, and the way it is calculated. 2. We found it to be theoretically incorrect, n ot supported by empirical data on maximum population density and body size relationships, and that its calculation is misleading, In particu lar, we found a general pattern underlying the allometry of maximum po pulation density, which stresses the correspondence between the docume nted linear patterns and triangular relationships between both variabl es. 3. Two independent data sets, one for mammals and another for inte rtidal invertebrates, showed that medium-size species attain higher po pulation densities, and that population density decreases towards larg er and smaller sizes. 4. A more direct calculation of population energ y use for mammalian primary consumers, based on measured metabolic rat es, showed that populations' energy use fluctuates widely among specie s and that its upper limit is not independent of body size but peaks a t a body size of about 100 g, and decreases toward both smaller and la rger body sizes. 5. Diet also has a strong effect on this relationship . Omnivores show a positive relationship between population energy use and body size, while this is negative for carnivores and insectivores .