title: An alternative explanation for global trends in thermal tolerance.
abstract: Ectotherms from higher latitudes can generally perform over broader temperature ranges than tropical ectotherms. This pattern is thought to reflect trends in temperature variability: tropical ectotherms evolve to be 'thermal specialists' because their environment is thermally stable. However, the tropics are also hotter, and most physiological rates increase exponentially with temperature. Using a dataset spanning diverse ectotherms, we show that the temperature ranges ectotherms tolerate (the difference between lower and upper critical temperatures, and between optimum and upper critical temperatures) generally represents the same range of equivalent biological rates (e.g. metabolism) for cool- and warm-adapted species, and independent of latitude or elevation. This suggests that geographical trends in temperature variability may not be the ultimate mechanism underlying latitudinal and elevational trends in thermal tolerance. Rather, we propose that tropical ectotherms can perform over a narrower range of temperatures than species from higher latitudes because the tropics are hotter.
authors.affiliation: National Institute of Polar Research, 10-3, Midori-cho, Tachikawa, Tokyo, 190-8518, Japan.|University of Roehampton, Holybourne Avenue, London, SW15 4JD, UK.
authors.forename: Nicholas L
authors.initials: NL
authors.lastname: Payne
authors.affiliation: University of New South Wales, High Street, Kensington, NSW, 2043, Australia.
authors.forename: James A
authors.initials: JA
authors.lastname: Smith
mesh_terms: D000818:Animals; D001181:Arthropods / Q000502:physiology*; D005075:Biological Evolution; D017753:Ecosystem; D013045:Species Specificity; D000071436:Thermotolerance; D014329:Tropical Climate; D014714:Vertebrates / Q000502:physiology*
keywords: Activation energy; Arrhenius-Boltzmann; Janzen's hypothesis; MTE; Rapoport's rule; climate change; macroecology; mountain passes; polar; thermal specialist