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| Climate change is altering phenology and distributions of many species and further changes are projected.
Can species physiologically adapt to climate warming? We analyse thermal tolerances of a large number of
terrestrial ectotherm (n = 697), endotherm (n = 227) and plant (n = 1816) species worldwide, and show
that tolerance to heat is largely conserved across lineages, while tolerance to cold varies between and within
species. This pattern, previously documented for ectotherms, is apparent for this group and for endotherms
and plants, challenging the longstanding view that physiological tolerances of species change continuously
across climatic gradients. An alternative view is proposed in which the thermal component of climatic
niches would overlap across species more than expected. We argue that hard physiological boundaries exist
that constrain evolution of tolerances of terrestrial organisms to high temperatures. In contrast, evolution
of tolerances to cold should be more frequent. One consequence of conservatism of upper thermal tolerances
is that estimated niches for cold-adapted species will tend to underestimate their upper thermal limits,
thereby potentially inflating assessments of risk from climate change. In contrast, species whose climatic
preferences are close to their upper thermal limits will unlikely evolve physiological tolerances to increased
heat, thereby being predictably more affected by warming. | |
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