Environments where extreme temperatures and low productivity occur introduce energetically challenging circumstances that may be exacerbated by climate change. Despite the strong link between metabolism and temperature in ectotherms, there is a paucity of data regarding how the metabolic ecology of species affects growth and fitness under such circumstances. Here, we integrated data describing field metabolic rates and body condition of two sympatric species of ectotherms with divergent lifestyles, the benthic freshwater (or largetooth) sawfish (Pristis pristis) and the epipelagic bull shark (Carcharhinus leucas) occurring in the Fitzroy River, Western Australia, to test the implications of their differing metabolic ecologies for vulnerability to rising temperatures. Over a temperature range of 18-34 °C, sawfish had lower field metabolic rates (63-187 mg O2 kg-0.86 h-1) and lower temperature sensitivity of metabolic rates [activation energy (EA) = 0.35 eV] than bull sharks (187-506 mg O2 kg-0.86 h-1; EA = 0.48 eV). Both species lost body mass throughout the dry season, although bull sharks significantly more (0.17% mass loss day-1) than sawfish (0.07% mass loss day-1). Subsequent bioenergetics modelling showed that under future climate change scenarios, both species would reach potentially lethal levels of mass loss during dry season periods before the end of the century. These results suggest that ectotherms with low metabolic rates may be better suited to extreme environmental conditions, and that even small increases in temperature due to climate change could have substantial impacts on the ability of ectotherms to grow and survive in harsh conditions, including high temperatures and energy-limiting circumstances.

中文翻译：

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不同的田间代谢速率突显了水外温升高温度和能量限制的挑战。

发生极端温度和低生产率的环境会带来充满挑战的环境，气候变化可能会加剧这种环境。尽管新陈代谢中的代谢与温度之间有很强的联系，但是在这种情况下，关于物种的代谢生态学如何影响生长和适应性的数据很少。在这里，我们综合了数据，描述了在西部菲茨罗伊河中发生的两种具有不同生活方式的同温放线虫的田间代谢率和身体状况，即底栖淡水（或大齿）锯鱼（Pristis pristis）和上上公鲨（Carcharhinus leucas）。澳大利亚，以测试他们不同的代谢生态学对温度升高的脆弱性的影响。在18-34°C的温度范围内，锯fish鱼的场代谢率较低（63-187 mg O2 kg-0.86 h-1），代谢温度对温度的敏感性[活化能（EA）= 0.35 eV]比公鲨（187-506 mg O2 kg-0.86 h- 1； EA = 0.48 eV）。这两个物种在整个干旱季节都失去了体重，尽管公鲨（第1天的质量损失为0.17％）比锯鱼（第1天的质量损失为0.07％）要多得多。随后的生物能学模型表明，在未来的气候变化情景下，两个物种在本世纪末之前的旱季期间都可能达到致命的质量损失水平。这些结果表明，代谢率低的外加温可能更适合极端环境条件，