Energy expenditure and water flux in three sympatric desert rodents.

Golden spiny mouse Acomys russatus (Muridae), common spiny mouse A. cahirinus and bushy-tailed jird Sekeetamys calurus (Gerbillidae) , are similar in body size and are sympatric in many rocky areas in Israeli deserts. They differ in that A. russatus and S. calurus inhabit extremely arid areas where A. cahirinus is absent, and A. russatus is diurnal, whereas the other 2 species are nocturnal. All 3 species maintained water and energy balances, and had similar mass-specific water influxes (c0.13 ml g^-1 d^-1), while consuming different proportions of dry, mature vegetation and insects. Insects provided 38% of the total dry matter intake for A. cahirinus, 62% for A. russatus and 87% for S. calurus. A. cahirinus (38.3 g body mass) had the highest energy flux and expended 1.35 kJ g^-1 d^-1 during its 10.5-h activity period. A. russatus (45.0 g) expended 1.06 kJ g^-1 d^-1 during its 9-h activity period and S. calurus (41.2 g) expended 1.07 kJ g^-1 d^-1 during its 10.5-h activity period. Water influxes of these 3 species were intermediate between those of other rodents, suggesting that behavioural diet selection can be as important as physiological water conservation in adapting to desert life. Their energy expenditures were lower than those predicted for rodents of their body mass, consistent with the notion of low energy expenditures among desert-adapted rodents. The ratio of water influx to dry matter intake (ml:g) was 1.3 in A. cahirinus, compared with 1.9 in A. russatus and 2.5 in S. calurus. Thus more water was available for evaporative cooling in the latter 2 species. This could explain, at least in part, their different geographical distributions. -from Authors