Macroecological patterns in European butterflies unveil strong interrelations between larval diet breadth, latitudinal range size and voltinism

Diet breadth is one of the fundamental species traits of an herbivorous insect as it strongly determines its ecological niche and, at the same time, its ability to cope with changing environmental conditions. To what extent this trait is associated with other characteristics that may influence a species' ability to respond to environmental changes, however, is yet poorly understood. Using European butterflies as a model group of holometabolous insect herbivores, we here tested whether larval diet breadth is positively related with latitudinal range size (i.e. north–south extent of global distribution), voltinism and adult body size. We further investigated whether range size, voltinism, and body size are associated with each other. In order to test for these relationships, we based our analyses on a solid, time-calibrated butterfly phylogeny as well as on an updated host plant database that reflects interactions between butterfly larvae and their food plants in a yet unparalleled breadth and depth. We further calculated two measures to reflect the fundamental dietary niche of a species: taxonomic diet breadth and phylogenetic diet breadth. Irrespective of diet breadth measure, we found that diet breadth increases with latitudinal range size. We further found an overall higher diet breadth for species that are capable to realise multiple broods per year (i.e. multivoltine species) compared to obligatorily univoltine species. Contrary to expectation, our results indicated a negative relationship between larval diet breadth and adult body size. Regarding our explorative analyses, we observed a positive link between voltinism and latitudinal range size, while neither one of these variables was associated with body size. Taken together, our study shows that larval diet breadth, latitudinal range size and voltinism are positively linked in European butterflies, and we argue that these interrelationships are important in determining a species' overall potential to cope with changing environmental conditions.