Global warming favours light-coloured insects in Europe
Associations between biological traits of animals and climate are well documented by physiological studies at local scales. However, the impact of ecophysiological processes on biogeographical patterns of insects is poorly documented. Many insect groups rely on external energy to reach the body temperature necessary for foraging or mating. Thereby their colouration determines the rate of energy absorption from the environment. Here we combine digital imaging techniques to characterize darkness respectively lightness of 366 butterfly and 107 dragonfly species and phylogenetic statistics in a spatial analysis across Europe to address the hypothesis that dark-coloured butterfly and dragonfly species are favoured in cooler climates and light-coloured species in warmer climates.
We found that the average colour lightness of butterfly and dragonfly assemblages is consistently correlated to the thermal environment across Europe. We furthermore found that assemblages of dragonflies became on average lighter-coloured during the last century, which we attribute to global warming. Our study provides thereby support for a mechanistic link between climate and functional traits of species that affects geographical distributions even at continental scales. Our results constitute a foundation for better forecasting of the effect of climate change on several insect groups.