Species turnover with elevation is a widespread phenomenon and provides valuable information on why and how ecological communities might reorganize as the climate warms. It is commonly assumed that species interactions are more likely to set warm range limits, while physiological tolerances determine cold range limits. However, most studies are from temperate systems and rely on correlations between thermal physiological traits and range limits; little is known about how physiological traits and biotic interactions change simultaneously along continuous thermal gradients. We used a combination of correlational and experimental approaches to investigate communities of Drosophila flies in rainforests of the Australian Wet Tropics, where there is substantial species turnover with elevation. Our experiments quantified individual-level and population-level responses to temperature, as well as the impact of interspecific competition under different temperature regimes. Species' distributions were better explained by their performance at extreme temperatures than by their thermal optima. Upper thermal limits varied less among species than lower thermal limits. Nonetheless, these small differences were associated with differences in the centered elevation of distribution. Low-elevation species were not those with the lowest tolerance to cold, suggesting that cold temperatures were not limiting their abundance at high elevations. Instead, under upland temperature regimes, abundances of these low-elevation species were reduced by competition with a high-elevation species, in both short- and long-term competition experiments. Our results demonstrate that high-elevation species are confined to their current ranges by high temperatures at lower elevations, indicating that their ranges will be highly sensitive to future warming. Counter to expectation, species interactions strongly influenced community composition at cooler, high-elevation sites. Together, these results raise the possibility that tropical communities differ from better-studied temperate communities in terms of the relative importance of biotic interactions and abiotic factors in shaping community composition and how the impact of these factors will change as temperatures increase.

中文翻译：

---

随着海拔的增加，热带山区物种分布的限制从高温转向竞争

随着海拔的升高，物种更替是一种普遍现象，并为生态群落随着气候变暖为何以及如何重组提供了宝贵的信息。通常认为，物种相互作用更有可能设定温暖范围限制，而生理耐受性则决定寒冷范围限制。然而，大多数研究都是来自温带系统，依赖于热生理特征和范围限制之间的相关性；人们对生理特征和生物相互作用如何沿着连续的温度梯度同时变化知之甚少。我们采用相关和实验相结合的方法来调查澳大利亚湿热带雨林中的果蝇群落，那里随着海拔的升高存在大量的物种更替。我们的实验量化了个体水平和群体水平对温度的反应，以及不同温度条件下种间竞争的影响。物种的分布可以通过它们在极端温度下的表现来更好地解释，而不是通过它们的最适温度来解释。不同物种间的热上限变化小于热限下限。尽管如此，这些微小的差异与分布中心高度的差异有关。低海拔物种并不是那些对寒冷的耐受性最低的物种，这表明寒冷的气温并没有限制它们在高海拔地区的丰度。相反，在高地温度条件下，在短期和长期竞争实验中，这些低海拔物种的丰度因与高海拔物种的竞争而减少。我们的研究结果表明，高海拔物种因低海拔地区的高温而被限制在其当前的范围内，这表明它们的范围将对未来的变暖高度敏感。与预期相反，物种相互作用强烈影响了凉爽、高海拔地区的群落组成。总之，这些结果提出了热带群落与经过深入研究的温带群落在生物相互作用和非生物因素在塑造群落组成方面的相对重要性以及这些因素的影响如何随着温度升高而变化方面存在差异的可能性。