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Meeting Abstract
Surprisingly, the thermal tolerances of species often do not match the range of environmental temperatures experienced within in the geographic range. Although a variety of hypotheses have been proposed to link thermal physiology and the thermal niche, support for these relationships is not consistent between taxonomic groups. According to the Scholander-Irving model of thermal physiology, a trade-off between the upper (TUC) and lower (TLC) bounds of the thermal neutral zone is predicted for endotherms. Such a trade-off may explain the discordance between species’ thermal tolerance and their thermal environment. Here, we employ a dataset of 297 mammal and 134 non-migratory bird thermal physiology to test for the predicted trade-off as well as investigate its role in the mismatch between species’ thermal physiology and their thermal environment. We show that a trade-off does indeed exist between upper and lower thermal critical temperatures for the majority of mammals and birds. Further, we find that the trade-off is asymmetrical with an increase in TUC corresponding to a disproportionate increase in TLC. Additionally, the trade-off plays a significant role in the mismatch between species’ thermal tolerances and their thermal environment. Evidence of this trade-off means that strong physiological constraints limit adaptations to extreme environmental temperatures.