Simulating climate change: temperature extremes but not means diminish performance in a widespread butterfly

Climate‐change induced shifts in species’ temporal and geographic niches have been well documented, while plastic and genetic responses to climatic change have received much less attention. Plastic responses to changes in temperature are generally well understood, though most experimental studies to date have used constant temperature regimes, the reliability of which is under debate. We here investigate plastic responses in the widespread butterfly Pieris napi to simulated climate change, using ecologically realistic diurnal temperature cycles and current and predicted temperature regimes including effects of a heat wave. Increasing the temperature mean by 3 °C predominantly affected developmental times, cold resistance and adult life span, while an increase in the diurnal temperature amplitude had very little effects. Immune function responded only weakly to different thermal regimes. The simulation of a prolonged heat wave severely impaired juvenile survival, body size and longevity, supporting the wide‐held notion that extreme weather events will be much more important for species’ performance and local survival than moderate increases in temperature means. Given that the frequency of extreme weather events is predicted to increase with climate change, even widespread species may be negatively affected.