Figure 5.24 Latitudinal variation in absolute maximum and minimum temperatures (open circles) and annual mean daily temperature (closed circles) across the New World.

Source: Gaston and Chown (1999). Oikos 84, 309-312, Blackwell Publishing.

Although spatial variation in upper and lower lethal limits, and the extent to which acclimation has an effect on them, is less variable at the intraspecific level (e.g. Hoffmann and Watson 1993), some studies have suggested that variation is greater in lower than in upper lethal limits. For example, intraspecific variation in critical thermal limits (CTmax and CTmin) in weevil species from sub-Antarctic Marion and Heard Islands varies substantially across altitudinal gradients (Klok and

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