Thermal trouble in the tropics

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Science  25 Mar 2016:
Vol. 351, Issue 6280, pp. 1392-1393
DOI: 10.1126/science.aaf3343

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Early Victorian naturalists marveled at the profusion of diversity they encountered as they traveled from temperate to tropical latitudes. The inverse relationship between latitude and species richness that these naturalists first observed is now referred to as the latitudinal diversity gradient. Various ecological and evolutionary explanations have been proposed for the latitudinal diversity gradient. Of these, perhaps none are more relevant to contemporary conservation issues than Janzen's hypothesis of latitudinal differences in species' climatic tolerances and thermal selectivity (1). On page 1437 of this issue, Chan et al. (2) advance Janzen's early theories by elucidating some of the potential selective pressures imposed by climate and climate variability.