RESEARCH PAPER The Eurasian hot nightlife: Environmental forces associated with nocturnality in lizards Enav Vidan 1 | Uri Roll 2,3 | Aaron Bauer 4 | Lee Grismer 5 | Peng Guo 6 | Erez Maza 1 | Maria Novosolov 1 | Roberto Sindaco 7 | Philipp Wagner 8,9 | Jonathan Belmaker 1,10 | Shai Meiri 1,10 1 Department of Zoology, Tel Aviv University, Tel Aviv, Israel 2 School of Geography and the Environment, University of Oxford, Oxford, United Kingdom 3 Mitrani Department of Desert Ecology, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel 4 Department of Biology, Villanova University, Villanova, Pennsylvania 5 Department of Biology, La Sierra University, Riverside, California 6 College of Life Science and Food Engineering, Yibin University, Yibin, Sichuan, China 7 Museo Civico di Sotria Naturale, Carmagnola, Turin, Italy 8 Zoologische Staatssammlung M€ unchen, M€ unchen, Germany 9 Department of Biology, Villanova University, Villanova, Pennsylvania 10 The Steinhardt Museum of Natural History, Tel Aviv University, Tel Aviv, Israel Correspondence Enav Vidan, Department of Zoology, Tel Aviv University, Tel Aviv 6997801, Israel. Email: enavidan@gmail.com Funding information Israel Science Foundation (ISF), Grant/ Award Number: 1005/12; Ben-Gurion University of the Negev Editor: Richard Grenyer Abstract Aim: Lizards are ancestrally diurnal, and most of them remain so. Nocturnality is common among lizards, but the environmental factors associated with lizard nocturnal activity are still unknown. Here, we contrasted the ambient temperature and productivity hypotheses, where we predicted that cold temperatures will pose a stonger limit to nocturnal species richness than diurnal lizards. Moreover, we contrasted the relative importance of annual, day and night mean temperatures to pinpoint the drivers of nocturnal lizard richness. Location: Mainland Eurasia. Methods: We collected distribution range and activity time data for all 1,113 lizard species found throughout mainland Eurasia. This represents the largest geographical scope to date, for studies of lizard species richness. We examined the spatial patterns of nocturnal species richness in relation- ship to diurnal species richness across environmental gradients of ambient temperature and productivity. Results: Nocturnal lizards are richest in the tropics and in deserts, and their richness decreases with latitude. However, nocturnal lizards are absent from the highest latitudes and coldest regions inhabited by lizards. Diurnal and nocturnal lizards respond in a similar manner to climatic factors. Ambient temperature has a strong influence on both, whereas productivity is more tightly related to the proportion of nocturnal species. Main conclusions: Nocturnality is widespread among Eurasian lizards. However, nocturnal lizards are absent from invariably cold regions, and low temperatures seem to be a limiting factor for liz- ard activity period. We suggest that the year-round warm nights of the tropics reduce the cost of being active at night and open the nocturnal niche for many lizards. In hot deserts, the combina- tion of hot days and aridity increases the cost of diurnal activity, whereas nocturnal activity provides a shelter from these extreme conditions. KEYWORDS ambient temperature hypothesis, night temperature, productivity hypothesis, richness 1 | INTRODUCTION Squamates are ancestrally diurnal, and the majority of the species, gen- era and families have remained so. Nocturnality, however, has evolved multiple times during the evolutionary history of the group (Vitt, Pianka, Cooper, & Schwenk, 2003). Nevertheless, as ectotherms, noc- turnal lizards need to cope with both lower nighttime temperatures and a lack of external heat source. The activity of ectotherms, such as lizards, depends primarily on external heat sources (Cowles & Bogert, 1944; Pianka & Vitt, 2003; 1316 | V C 2017 John Wiley & Sons Ltd wileyonlinelibrary.com/journal/geb Global Ecol Biogeogr. 2017;26:1316–1325. Received: 1 February 2017 | Revised: 9 May 2017 | Accepted: 26 May 2017 DOI: 10.1111/geb.12643