Munn A J, Dawson T J
School of Biological Science, University of New South Wales, Sydney, New South Wales 2052, Australia.
Physiol Biochem Zool. 2001 Nov-Dec;74(6):917-27. doi: 10.1086/324568.
The population dynamics of red kangaroos (Macropus rufus) in the Australian arid zone is tightly linked with environmental factors, which partly operate via the survival of juvenile animals. A crucial stage is the young-at-foot (YAF) stage when kangaroos permanently exit the pouch. We have examined the thermal biology of YAF red kangaroos during ages from permanent pouch exit until weaning. Over a wide range of environmental temperatures (ambient temperature [T(a)] -5 degrees to 45 degrees C), YAF red kangaroos had a mass-specific metabolism that was generally twice that of adults, considerably higher than would be expected for an adult marsupial of their body size. The total energy requirements of YAF red kangaroos were 60%-70% of those of adult females, which were three times their size. Over the same range in T(a), YAF red kangaroos also had total evaporative water losses equal to those of adult females. At the highest T(a) (45 degrees C), differences were noted in patterns of dry heat loss (dry conductance) between YAF red kangaroos and adult females, which may partially explain the relatively high levels of evaporative cooling by YAF. By weaning age, young kangaroos showed little change in their basal energy and water requirements (at T(a) 25 degrees C) but did show reduced mass-specific costs in terms of energy and water use at extremes of T(a) (-5 degrees and 45 degrees C, respectively). In their arid environment, typified by unpredictable rainfall and extremes of T(a), young red kangaroos may need to remain close to water points, which, in turn, may restrict their ability to find the high-quality forage needed to meet their high energy demands.
澳大利亚干旱地区红袋鼠（Macropus rufus）的种群动态与环境因素紧密相连，环境因素部分通过幼崽的存活发挥作用。一个关键阶段是幼袋鼠（YAF）阶段，即袋鼠永久性地离开育儿袋。我们研究了从永久性离开育儿袋到断奶期间幼袋鼠的热生物学特性。在广泛的环境温度范围内（环境温度[T(a)]为-5摄氏度至45摄氏度），幼袋鼠的质量比代谢率通常是成年袋鼠的两倍，大大高于同等体型成年有袋动物的预期值。幼袋鼠的总能量需求是成年雌性袋鼠的60%-70%，而成年雌性袋鼠的体型是幼袋鼠的三倍。在相同的T(a)范围内，幼袋鼠的总蒸发失水量与成年雌性袋鼠相同。在最高T(a)（45摄氏度）时，幼袋鼠和成年雌性袋鼠在干热损失模式（干传导率）上存在差异，这可能部分解释了幼袋鼠相对较高的蒸发冷却水平。到断奶期时，幼袋鼠在基础能量和水分需求方面（在T(a) 25摄氏度时）变化不大，但在T(a)极端值（分别为-5摄氏度和45摄氏度）时，其在能量和水分使用方面的质量比成本确实有所降低。在以降雨不可预测和T(a)极端值为特征的干旱环境中，幼小的红袋鼠可能需要靠近水源点，而这反过来可能会限制它们找到满足其高能量需求所需优质草料的能力。
