Coming home: Back-introduced invasive genotypes might pose an underestimated risk in the species´ native range

Biological invasions are considered a significant challenge both from an ecological and economical perspective. Compared to the native range, environmental conditions in the invasive range often favor more competitive genotypes. Little attention, however, has so far been paid to the possibility that these invasive and competitive genotypes might also be back-introduced into a species’ native range, where they could trigger a problematic increase in abundance or expansion. The frequency with which this occurs in the species´ native range might be an underestimated aspect in nature conservation. We transplanted native and invasive individuals of the biennial model species Jacobaea vulgaris into field sites of naturally occurring populations within the species’ native range. The aim was to test whether back-introduced invasive origins show decreased performance, e.g., because of the reunion with specialized herbivores or plant-soil-feedbacks or whether they have the potential to trigger problematic population dynamics in the species’ native range. We ran an additional greenhouse experiment to specifically address soil-borne effects in the species’ native habitats. We found that invasive individuals generally outperformed the native transplants if compared in the field sites. By contrast, there were no origin-dependent differences in the greenhouse experiment. Our findings clearly indicate that testing for origin effects exclusively under controlled conditions might underestimate the potential of invasive genotypes to trigger invasion processes in habitats of the species’ native range. Although differences in performance mediated by soil-borne effects were not associated with plant origin, field site susceptibility to J. vulgaris colonization varied largely. Identifying the exact factors driving these differences, offers another focal point to minimize the risk of a detrimental increase in the abundance or expansion of this highly invasive species in its home range.