Data from: Comparing macroecological patterns across continents: evolution of climatic niche breadth in varanid lizards

Macroecological analyses often test hypotheses at the global scale, or among more closely related species in a single region (e.g. continent). Here, we test several hypotheses about climatic niche widths among relatively closely related species that occur across multiple continents, and compare patterns within and across continents to see if they differ. We focus on the lizard genus Varanus (monitor lizards), which occurs in diverse environments in Africa, Asia, and Australia. We address three main questions. (1) How do climatic niche breadths of species on a given niche axis change based on the position of species along that niche axis? (e.g. are species that occur in more extreme environments more narrowly specialized for those conditions?) (2) Are there trade-offs in niche breadths on temperature and precipitation axes among species, or are niche widths on different axes positively related? (3) Is variation in niche breadths among species explained primarily by within-locality seasonal variation, or by differences in climatic conditions among localities across the species range? We generate a new time-calibrated phylogeny for Varanus and test these hypotheses within and between continents using climatic data and phylogenetic methods. Our results show that patterns on each continent often parallel each other and global patterns. However, in many other cases, the strength of relationships can change dramatically among closely related species on different continents. Overall, we found that: (1) species in warmer environments have narrower temperature niche breadths, but there is no relationship between precipitation niche breadth and niche position; (2) temperature and precipitation niche breadths tend to be positively related among species, rather than showing trade-offs; (3) within-locality seasonal variation explains most variation in climatic niche breadths. Some of these results are concordant with previous studies (in amphibians and North American lizards), and might represent general macroecological patterns.

宏观生态学（macroecological）分析通常在全球尺度开展假说检验，或是在单一地理区域（如大陆）内的近缘物种类群中进行。本研究针对分布于多个大陆的近缘物种类群，检验多项关于气候生态位宽度（climatic niche widths）的假说，并对比各大陆内部及跨大陆的格局差异，以探究二者是否存在差异。

本研究聚焦于巨蜥属（Varanus，monitor lizards），该类群在非洲、亚洲及澳大利亚的多样生境中均有分布。我们提出三个核心研究问题：
1. 在特定生态位轴（niche axis）上，物种的气候生态位宽度会如何随物种在该轴上的位置发生变化？例如，栖息于极端环境中的物种，是否对该类环境具备更窄的特化适配性？
2. 物种在温度轴与降水轴上的生态位宽度是否存在权衡关系，抑或不同轴上的生态位宽度呈正相关？
3. 物种间生态位宽度的变异，主要由局地尺度的季节变异（within-locality seasonal variation）解释，还是由物种分布范围内各局地的气候条件差异所决定？

我们为巨蜥属构建了全新的时间校准系统发育树（time-calibrated phylogeny），并结合气候数据与系统发育分析方法（phylogenetic methods），在各大陆内部及跨大陆尺度下检验上述假说。

研究结果显示，各大陆的格局通常与全球格局保持一致。但在诸多其他情形中，不同大陆上近缘物种类群间的关联强度会发生显著变化。

总体而言，我们的研究发现如下：
1. 栖息于温暖环境中的物种，其温度生态位宽度更窄，但降水生态位宽度与生态位位置之间不存在相关性；
2. 物种的温度与降水生态位宽度通常呈正相关，而非存在权衡关系；
3. 局地尺度的季节变异可解释绝大多数气候生态位宽度的变异。

部分研究结果与此前针对两栖动物及北美蜥蜴的研究结论一致，或可代表普适性的宏观生态学格局。