Centre for Tropical Biodiversity and Climate Change, School of Marine and Tropical Biology, James Cook University, P.O. Box 6811, Cairns, QLD, 4870, Australia.
Oecologia. 2012 Apr;168(4):889-99. doi: 10.1007/s00442-011-2146-2. Epub 2011 Oct 11.
Models of impacts of climate change on species are generally based on correlations between current distributions and climatic variables, rather than a detailed understanding of the mechanisms that actually limit distribution. Many of the vertebrates endemic to rainforests of northeastern Australia are restricted to upland forests and considered to be threatened by climate change. However, for most of these species, the factors controlling their distributions are unknown. We examined the role of thermal intolerance as a possible mechanism limiting the distribution of Pseudochirops archeri (green ringtail possum), a specialist arboreal folivore restricted to rainforests above an altitude of 300 m in Australia's Wet Tropics. We measured short-term metabolic responses to a range of ambient temperatures, and found that P. archeri stores heat when ambient temperatures exceed 30°C, reducing water requirements for evaporative cooling. Due to the rate at which body temperature increases with ambient temperatures >30°C, this strategy is not effective over periods longer than 5 h. We hypothesise that the distribution of P. archeri is limited by interactions between (i) the duration and severity of extreme ambient temperatures (over 30°C), (ii) the scarcity of free water in the rainforest canopy in the dry season, and (iii) constraints on water intake from foliage imposed by plant secondary metabolites and fibre. We predict that dehydration becomes limiting for P. archeri where extreme ambient temperatures (>30°C) persist for more than 5 h per day over 4-6 days or more. Consistent with our hypothesis, the abundance of P. archeri in the field is correlated with the occurrence of extreme temperatures, declining markedly at sites where the average maximum temperature of the warmest week of the year is above 30°C. Assuming the mechanism of limitation is based on extreme temperatures, we expect impacts of climate change on P. archeri to occur in discrete, rapid events rather than as a slow contraction in range.
物种气候变化影响模型通常基于当前分布与气候变量之间的相关性，而不是对实际限制分布的机制的详细了解。澳大利亚东北部热带雨林特有的许多脊椎动物仅限于高地森林，被认为受到气候变化的威胁。然而，对于这些物种中的大多数来说，控制它们分布的因素是未知的。我们研究了热不耐受作为一种可能的机制，限制了 Pseudochirops archeri（绿环尾袋貂）的分布，这种专门的树栖食叶动物只限于澳大利亚潮湿热带地区海拔 300 米以上的雨林中。我们测量了对一系列环境温度的短期代谢反应，发现当环境温度超过 30°C 时，P. archeri 会储存热量，从而减少蒸发冷却所需的水分。由于体温随环境温度升高的速度超过 30°C，这种策略在超过 5 小时的时间内是无效的。我们假设 P. archeri 的分布受到以下因素之间的相互作用的限制：（i）极端环境温度（超过 30°C）的持续时间和严重程度；（ii）旱季雨林冠层中自由水的稀缺性；以及（iii）植物次生代谢物和纤维对从树叶中摄入水分的限制。我们预测，当极端环境温度（>30°C）每天持续超过 5 小时且持续 4-6 天或更长时间时，脱水对 P. archeri 来说将变得有限。与我们的假设一致，P. archeri 在野外的丰度与极端温度的发生相关，在一年中最热一周的平均最高温度超过 30°C 的地点，其丰度显著下降。假设限制机制基于极端温度，我们预计气候变化对 P. archeri 的影响将以离散的、快速的事件发生，而不是范围的缓慢收缩。
