Newly introduced butterfly species' urban habitat use driven by shorter vegetation and exotic plants

The successful establishment of an exotic species is based on its resource-based habitat, and thus depends on its encountering the interaction partners and environmental conditions it requires to complete its life cycle. We examine factors that define the resource-based habitat of the European common blue butterfly (Polyommatus icarus Rottemburg, [1775] (Lepidoptera: Lycaenidae)) recently introduced in Quebec, testing the role of exotic host plants and of short vegetation structure. Field studies surveyed adult butterfly abundance in lightly managed urban sites and related it to host plant cover and vegetation structure. Oviposition behavior was also recorded and linked to individual plant traits, namely height, species and anatomical structures. Results show that adult butterflies maintain the same host plant associations as in the native range, suggesting a role for naturalized plants in facilitating the establishment of this exotic herbivore. However, relative oviposition rate was not higher on the most strongly associated host plant (birdsfoot trefoil, Lotus corniculatus, Fabaceae) suggesting no clear behavioral preference for this plant. Butterflies also showed the same association with short vegetation documented in the native range, although the basis for this preference remains unclear. P. icarus uses different biotopes in its invaded range (lightly managed urban sites) than in its native range (unimproved grasslands), and our results show the role of host plants and of short vegetation structure in defining the resource-based habitat that can predict its future expansion. Our results raise interesting questions about why this butterfly uses cities more in its invaded than its native range. The role of cities in insect conservation is increasingly recognized; we show how, paradoxically, a butterfly whose native biotopes are declining has found suitable conditions to thrive in far-removed urban centers.