Using biological traits to explain ladybird distribution patterns

Aim: Determining to what extent differing distribution patterns are governed by species’ life-history and resource-use traits may lead to an improved understanding of the impacts of environmental change on biodiversity. We investigated the extent to which traits can explain distribution patterns in the ladybird fauna (Coleoptera: Coccinellidae) of Great Britain. Location: The British mainland and inshore islands (Anglesey, the Isle of Wight and the Inner Hebrides). Methods: The distributions of 26 ladybird species resident in Britain were characterized in terms of their range size (from 2661 10-km grid squares across Britain) and proportional range fill (at 10- and 50-km scales). These were assessed relative to five traits (body length, elytral colour pattern polymorphism, voltinism, habitat specificity and diet breadth). The role of phylogenetic autocorrelation was examined by comparing the results of phylogenetic and generalized least-squares regressions. Results: Diet breadth was the only trait correlated with range size: species with broad diets had larger range sizes than dietary specialists. Range fill was sensitive to recording intensity (a per-species measure of the mean number of records across occupied squares); models including both recording intensity and range size provided more explanatory power than models incorporating ecological traits alone. Main conclusions: Habitat specificity is often invoked to explain the distribution patterns of species, but here we found diet breadth to be the only ecological correlate of both range fill and range size. This highlights the importance of understanding predator–prey interactions when attempting to explain the distribution patterns of predatory species. Our results suggest that the diet breadth of predatory species is a better correlate of range size and fill than other measures, such as habitat specificity.