Centre for Tropical Environmental and Sustainability Science, College of Science & Engineering, James Cook University, Townsville, Queensland, 4811, Australia.
Department of Wildlife Ecology and Conservation, University of Florida, Gainesville, Florida, 32611, USA.
Ecology. 2022 Jan;103(1):e03549. doi: 10.1002/ecy.3549. Epub 2021 Nov 21.
Determining how species thermal limits correlate with climate is important for understanding biogeographic patterns and assessing vulnerability to climate change. Such analyses need to consider thermal gradients at multiple spatial scales. Here we relate thermal traits of rainforest ants to microclimate conditions from ground to canopy (microgeographic scale) along an elevation gradient (mesogeographic scale) and calculate warming tolerance to assess climate change vulnerability in the Australian Wet Tropics Bioregion. We test the thermal adaptation and thermal niche asymmetry hypotheses to explain interspecific patterns of thermal tolerance at these two spatial scales. We tested cold tolerance (CT ), heat tolerance (CT ), and calculated thermal tolerance range (CT ), using ramping assays for 74 colonies of 40 ant species collected from terrestrial and arboreal habitats at lowland and upland elevation sites and recorded microclimatic conditions for one year. Within sites, arboreal ants were exposed to hotter microclimates and on average had a 4.2°C (95% CI: 2.7-5.6°C) higher CT and 5.3°C (95% CI: 3.5-7°C) broader CT than ground-dwelling ants. This pattern was consistent across the elevation gradient, whether it be the hotter lowlands or the cooler uplands. Across elevation, upland ants could tolerate significantly colder temperatures than lowland ants, whereas the change in CT was less pronounced, and CT did not change over elevation. Differential exposure to microclimates, due to localized niche preferences, drives divergence in CT , while environmental temperatures along the elevation gradient drive divergence in CT . Our results suggest that both processes of thermal adaptation and thermal niche asymmetry are at play, depending on the spatial scale of observation, and we discuss potential mechanisms underlying these patterns. Despite the broad thermal tolerance range of arboreal rainforest ants, lowland arboreal ants had the lowest warming tolerance and may be most vulnerable to climate change.
确定物种的热极限与气候的相关性对于理解生物地理格局和评估对气候变化的脆弱性非常重要。此类分析需要考虑多个空间尺度的热梯度。在这里，我们将热带雨林蚂蚁的热特性与沿海拔梯度（中地理尺度）的从地面到树冠的微气候条件（微观地理尺度）相关联，并计算升温耐受性以评估澳大利亚潮湿热带生物区系地区的气候变化脆弱性。我们测试了热适应和热生态位不对称假设，以解释这两个空间尺度上种间热耐受性的模式。我们使用斜坡试验测试了 40 种蚂蚁的 74 个殖民地的耐寒性（CT ）、耐热性（CT ）和计算的热耐受性范围（CT ），这些蚂蚁来自低地和高地海拔的陆地和树栖生境。在每个站点内，树栖蚂蚁暴露在更热的微气候中，平均 CT 比地面蚂蚁高 4.2°C（95%置信区间：2.7-5.6°C），CT 宽 5.3°C（95%置信区间：3.5-7°C）。这种模式在整个海拔梯度上都是一致的，无论是在更热的低地还是更冷的高地。在整个海拔范围内，高地蚂蚁可以比低地蚂蚁耐受更低的温度，而 CT 的变化不那么明显，并且 CT 不会随海拔而变化。由于局部生态位偏好导致的微气候差异导致 CT 的差异，而沿海拔梯度的环境温度则导致 CT 的差异。我们的结果表明，取决于观察的空间尺度，热适应和热生态位不对称这两个过程都在发挥作用，我们讨论了这些模式的潜在机制。尽管树栖热带雨林蚂蚁的热耐受性范围很广，但低地树栖蚂蚁的升温耐受性最低，可能最容易受到气候变化的影响。
