Generalist-specialist continuum and life history traits of Central European butterflies (Lepidoptera) - are we missing a part of the picture?

Analyzing life history traits of butterfly communities and faunas frequently reveals a generalist-specialist continuum as the main gradient, where species using wide arrays of resources, with good dispersal ability and fast development are distinguished from those using specialised resources, having limited dispersal ability and developing slowly. To ascertain the validity of the generalist-specialist approach for an intermediately species-rich Central European fauna, we analyzed ten life history traits for 136 species of butterflies currently occurring in the Czech Republic, using principal correspondence analysis (PCA) and controlling for phylogeny. The main gradient extracted indeed revealed a generalist-specialist continuum, while the gradient perpendicular to the main axis distinguished between small-bodied polyvoltine species feeding on small herbaceous plants and large-bodied monovoltine species feeding on grasses or woody plants. We coin "constrained voltinism continuum" for the second gradient and argue that it reflects the effect of anti-herbivore strategies of larval host plants on butterfly development. The position of the butterflies in the PCA ordination mirrors the C-S-R (Competitors - Stress tolerators - Ruderals) strategies of their host plants. Butterflies that feed on C- and R-selected plants tend to be generalists, but differ in voltinism, whereas specialists tend to feed on S-selected plants. Regressing measures of current conservation status of individual species in the Czech Republic against the two extracted life history gradients yielded a significant but weak response for the generalist-specialist continuum and no response for the constrained voltinism continuum. The weak responses were due to a wide scatter of status measures among "mid generalists". The generalist-specialist continuum is hence a rather poor predictor of species conservation status. Species of high conservation concern are found either among specialists, or among mid generalists with low to intermediate values on the constrained voltinism axis.