Diel thermal variability does not always have detrimental effects on the performance of ectotherms

Abstract Climate change directly affects animal survival, with ectotherms being particularly vulnerable because their vital rates are closely related to environmental temperatures. Using predictions from thermal performance curves of ectotherms as a framework, we conducted a meta‐analysis of published evidence to assess whether diel thermal variability affected ectotherm performance in relation to optimal temperatures, inflection point within the suboptimal temperature range, type of performance trait and duration of thermal treatments. Results showed that diel thermal variability reduced ectotherm performance when temperatures were within optimal or supra‐optimal ranges. In contrast, thermal variability increased performance when temperatures were below the inflection point in the suboptimal range and had no effect when temperatures were above the inflection point within the suboptimal range. The effects of diel thermal variability on ectotherm performance were stronger on population traits than on organismal traits, with intermediate effects on physiological traits. Furthermore, thermal variability effects had similar magnitude whether applied to single or multiple‐consecutive life stages. Our findings highlight the critical importance of optimal body temperatures, inflection points within the suboptimal temperature range, and type of performance trait for accurately determining the effects of thermal variability on ectotherm performance. Read the free Plain Language Summary for this article on the Journal blog.