Rising global temperatures are threatening biodiversity. Studies on the impact of temperature on natural populations usually use lethal or viability thresholds, termed the 'critical thermal limit' (CTL). However, this overlooks important sublethal impacts of temperature that could affect species' persistence. Here we discuss a critical but overlooked trait: fertility, which can deteriorate at temperatures less severe than an organism's lethal limit. We argue that studies examining the ecological and evolutionary impacts of climate change should consider the 'thermal fertility limit' (TFL) of species; we propose that a framework for the design of TFL studies across taxa be developed. Given the importance of fertility for population persistence, understanding how climate change affects TFLs is vital for the assessment of future biodiversity impacts.
Keywords: critical thermal limits; reproduction; species distributions; thermal fertility limits; thermal tolerance.
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