Scaling of energy and water fluxes in free-living arid-zone Australian marsupials

Rates of field metabolism and water influx of 6 endangered species of marsupials living on Barrow Island, Western Australia, were measured using doubly labeled water. Field metabolic rates (FMRs) of these arid-habitat species are related to body mass according to the following equation: FMR (kJ/day) = 9.58 g(0.539) (r(2) = 0.935). The allometric equation for water influx rates (WIRs) in 9 arid-habitat species or subspecies obtained in our study and from the literature is as follows: WIR (ml H2O/day) = 0.777 g(0.693) (r(2) = 0.848). These relationships indicate that marsupials from arid-habitats use about 35% less energy and water each day than do marsupials from nonarid habitats, Food intake for arid-zone marsupials may be estimated from the following equation: dry matter intake (g/day) = 0.501 g(0.601) (r(2) = 0.977). A water-economy index indicates that 3 of 6 species studied probably drank standing water, but 2 species may not have drunk water to maintain body mass during the rainless study period. The remarkably similar reduction in daily energy and water needs of arid versus nonarid Australian marsupials, compared with arid versus nonarid North American and African eutherians, suggests that this similarity is an example of convergent evolution.