Scaling the Ecological Cost of Transport to Body Mass in Terrestrial Mammals

The Ecological Cost of Transport (ECT) is defined as the percentage of a free-living animal's Daily Energy Expenditure (DEE) that is attributable to transport costs. It is concluded that the ECT must be an increasing function of body mass, with the result that some small mammals may have a very low ECT (<1% DEE) whereas large mammals may have an ECT of 5%-15% or more. For small mammals, or those that move little, daily transport costs would seem to be of little energetic significance. Daily Movement Distance (DMD) scales approximately as M0.25, in contrast to home range area, which scales approximately as M1.0. This discrepancy in scaling exponents is partially explained by a model which relates home range size, stomach capacity, and daily food consumption to yield an estimate of Daily Foraging Distance, the latter being quite similar to the empirically derived equation for DMD. Members of the order Carnivora move an average of 4.4 times as far as other mammals on a daily basis; therefore, Carnivora should spend considerably more on transport costs than do most other mammals. The ECT is discussed in the context of arguments concerning the energetic significance of the cost of locomotion and its relevance to the origin of locomotory specializations.