Ecophysiological hierarchies.
Among bovids, antelopes, rodents and marsupials--in fact, probably in most animals--the rates of energy and water turnover are linked to salt tolerance, renal concentration and protein synthesis rates. Evolution in wet areas is associated with high turnover rates and low salt tolerance, while desert derivation goes with low rate functions and high salt tolerance. This basic ecophysiology changes slowly, and animals that migrate to different environments may retain ancient patterns in areas where they seem inappropriate--so that cattle keep their high rates of energy and water use in arid zones, or llamas remain low in energy and water turnover after three million years in cool or wet environments. The rate functions may be linked through gene-controlled rates of protein synthesis and turnover, which evolved to run at high rates in well-supplied areas, and at low rates in the face of the sparse resources of the desert.