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 season...