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 of realising
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.