Biogeographical comparison of the invasive Lepidium draba in its native, expanded and introduced ranges

Abstract

Invasive plants are expected to perform better and consequently be more abundant in their introduced compared to their native ranges. However, few studies have simultaneously compared plant and population traits along with biotic and abiotic environmental parameters for invasive and native plant populations. We compared 17 native Eastern European, 14 expanded Western European and 31 introduced US populations of the invasive Lepidium draba over 2 years. Most parameters were similar between the two European ranges, but differed for the US. Density, cover, and biomass of L. draba were greater in the US while cover of other vegetation was lower. Bare-ground and litter cover were greater for US populations in 1 year, as was L. draba shoot height and seed output. Availability of labile soil nitrogen was also greater in the US range. Endophagous shoot herbivory was greater in Western Europe compared to the US in 1 year. As expected, specialist herbivores were only found in Europe. Differences between ranges were not explained by varying environmental conditions (climate, altitude and latitude). In summary our results indicate that lower interspecific competition, higher resource availability and the lack of specialist natural enemies may all contribute to the increased performance of L. draba in its introduced US range. Additionally, L. draba is well adapted to disturbance events, which may further benefit its competitiveness at degraded sites. In general our results were consistent between years, which reinforces their validity. However, some of the differences were only significant in one of the 2 years, which, on the other hand, emphasizes the importance to ideally conduct biogeographic comparisons over multiple years. © 2012 Springer Science+Business Media B.V.