Kudzu in Europe: niche conservatism for a highly invasive plant

Niche dynamics represent an important element in predicting potential invasion areas of alien species and their impacts as well as in understanding mechanisms underlying invasion success. Pueraria lobata, commonly named “kudzu”, is an Asian vine and one of the 100 worst invasive species in the world. In Europe, it is a serious pest although its distribution is quite localized. At present, no detailed information about niche dynamics following its introduction to Europe is available, so it is not known whether the plant has shifted its niche or not, as well as whether it has filled the whole available climatic niche. To fill this gap of knowledge, we applied the unified COUE (i.e., centroid shift, overlap, unfilling, and expansion) framework to evaluate the shift in the climatic niche in the invasive with respect to the native range. According to our analysis, kudzu showed climatic niche conservatism following its introduction to Europe: we detected a shift in the position of centroids of native and invasive niche of kudzu, likely due to a difference in climate availability rather than to a colonization of novel climatic conditions. In Europe, kudzu is occupying a subset of the climate of the native range, mainly characterized by colder and drier conditions than those characterizing the Asian Pacific range of the plant. These conditions are marginal and rarely experienced by the plant in its native range. Furthermore, the absence of any niche expansion indicates that a spread to novel climates should be excluded for the European kudzu. The high niche unfilling suggests that kudzu has not yet occupied the majority of suitable climates available in Europe, even if, climatic conditions similar to its native range are not so widespread in Europe. Multivariate environmental similarity surface analysis suggests that it may expand its European range. Thus, it is pivotal that measures of prevention, early detection and monitoring are timely and effectively implemented to avoid its spread throughout Europe.