Invasion of Pieris mannii butterflies across Central Europe facilitated by urbanization

Abstract

Urbanization progresses world-wide and the frequency of biological invasions increases. Understanding to what extent urban environments facilitate biological invasions and how this affects ecosystems within and outside urbanized areas thus becomes crucial. We here examine the role of urban environments in the invasion of the butterfly Pieris mannii that expanded across Central Europe within the last two decades. Using standardized butterfly captures at paired urban and (semi)natural field sites within the invaded range in Switzerland, we demonstrate that P. mannii is strongly associated with cities and towns. At least at some urban localities, this species is now the most common butterfly, and abundances tend to be particularly high where urban areas are large. Urbanization has thus clearly promoted the species’ rapid invasion because this butterfly is pre-adapted to non-native host plants common in urban environments, and perhaps also to the physical structure of urban habitats. Studying phenology over an entire season, we further infer that P. mannii has up to six generations per year, which may allow the species to adjust its life cycle to changing season length during northward expansion. Elucidating the origin of the range-expansive population and investigating potential ecological consequences of the invasion are exciting next steps to understanding this butterfly invasion.