Energy Expenditure and Water Flux in Three Sympatric Desert Rodents

SUMMARY Acomys cahirinus, and the 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 two species are nocturnal. (2) We estimated their field metabolic rates and water fluxes with doubly-labelled water, and determined diets, feeding rates, and activity periods during spring in order to evaluate questions concerning their desert adaptations and their different geographical distributions. We devised a method for determining the proportions of two food types (e.g. leaves and insects) consumed by non-drinking, free-ranging animals, using doubly-labelled water measurements and diet composition analyses. (3) All three species maintained water and energy balances, and had similar mass-specific water influxes (about 0.13 ml g-1 d-1), while consuming different proportions of dry, mature vegetation and insects. We estimated that 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 daily energy flux of the three species and expended 1.35 kJ g-~ d-' during its 10.5-h activity period. A. russatus (45.0 g) expended 1.06 kJ g-~ d-~ during its 9-h activity period and S. calurus (41.2 g) expended 1.07 kJ g-~ d-~ during its 10.5-h activity period. (4) Water influxes of these three 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, which is 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, as compared with 1-9 in A. russatus and 2.5 in S. calurus. Thus we assumed more water was available for evaporative cooling in the latter two species and concluded that this could explain, at least in part, their different geographical distributions. SUMMARY (1) The golden spiny mouse, Acomys russatus (Muridae), the common spiny mouse, Acomys cahirinus, and the 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 two species are nocturnal. (2) We estimated their field metabolic rates and water fluxes with doubly-labelled water, and determined diets, feeding rates, and activity periods during spring in order to evaluate questions concerning their desert adaptations and their different geographical distributions. We devised a method for determining the proportions of two food types (e.g. leaves and insects) consumed by non-drinking, free-ranging animals, using doubly-labelled water measurements and diet composition analyses. (3) All three species maintained water and energy balances, and had similar mass-specific water influxes (about 0.13 ml g-1 d-1), while consuming different proportions of dry, mature vegetation and insects. We estimated that 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 daily energy flux of the three species and expended 1.35 kJ g-~ d-' during its 10.5-h activity period. A. russatus (45.0 g) expended 1.06 kJ g-~ d-~ during its 9-h activity period and S. calurus (41.2 g) expended 1.07 kJ g-~ d-~ during its 10.5-h activity period. (4) Water influxes of these three 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, which is 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, as compared with 1-9 in A. russatus and 2.5 in S. calurus. Thus we assumed more water was available for evaporative cooling in the latter two species and concluded that this could explain, at least in part, their different geographical distributions. SUMMARY (1) The golden spiny mouse, Acomys russatus (Muridae), the common spiny mouse, Acomys cahirinus, and the 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 two species are nocturnal. (2) We estimated their field metabolic rates and water fluxes with doubly-labelled water, and determined diets, feeding rates, and activity periods during spring in order to evaluate questions concerning their desert adaptations and their different geographical distributions. We devised a method for determining the proportions of two food types (e.g. leaves and insects) consumed by non-drinking, free-ranging animals, using doubly-labelled water measurements and diet composition analyses. (3) All three species maintained water and energy balances, and had similar mass-specific water influxes (about 0.13 ml g-1 d-1), while consuming different proportions of dry, mature vegetation and insects. We estimated that 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 daily energy flux of the three species and expended 1.35 kJ g-~ d-' during its 10.5-h activity period. A. russatus (45.0 g) expended 1.06 kJ g-~ d-~ during its 9-h activity period and S. calurus (41.2 g) expended 1.07 kJ g-~ d-~ during its 10.5-h activity period. (4) Water influxes of these three 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, which is 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, as compared with 1-9 in A. russatus and 2.5 in S. calurus. Thus we assumed more water was available for evaporative cooling in the latter two species and concluded that this could explain, at least in part, their different geographical distributions. SUMMARY (1) The golden spiny mouse, Acomys russatus (Muridae), the common spiny mouse, Acomys cahirinus, and the 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 two species are nocturnal. (2) We estimated their field metabolic rates and water fluxes with doubly-labelled water, and determined diets, feeding rates, and activity periods during spring in order to evaluate questions concerning their desert adaptations and their different geographical distributions. We devised a method for determining the proportions of two food types (e.g. leaves and insects) consumed by non-drinking, free-ranging animals, using doubly-labelled water measurements and diet composition analyses. (3) All three species maintained water and energy balances, and had similar mass-specific water influxes (about 0.13 ml g-1 d-1), while consuming different proportions of dry, mature vegetation and insects. We estimated that 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 daily energy flux of the three species and expended 1.35 kJ g-~ d-' during its 10.5-h activity period. A. russatus (45.0 g) expended 1.06 kJ g-~ d-~ during its 9-h activity period and S. calurus (41.2 g) expended 1.07 kJ g-~ d-~ during its 10.5-h activity period. (4) Water influxes of these three 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, which is 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, as compared with 1-9 in A. russatus and 2.5 in S. calurus. Thus we assumed more water was available for evaporative cooling in the latter two species and concluded that this could explain, at least in part, their different