1. Understanding how non-native plants respond to environmental variation, and the limits to these responses, is important for predicting plant invasiveness. Until now, the extent to which species climatic limits differ on introduction to a new range has not been experimentally tested. Here, we investigate fitness responses to temperature and low-temperature limits to reproduction of native and introduced populations of the widespread forb Plantago lanceolata.
2. We recorded fitness parameters of P. lanceolata accessions collected from nearly complete latitudinal gradients in the species' native and introduced ranges and grown in five common gardens arranged along an elevational gradient in the native range (European Alps). The highest garden was located outside the low-temperature limit of the species.
3. Native populations exhibited clear clinal genetic differentiation along temperature gradients, while any differentiation in introduced populations was much weaker; however, the introduced populations displayed higher average fitness and broad climatic tolerance. Despite these differences, both native and introduced plants failed to set seed beyond the elevational range margin and so shared a similar low-temperature limit to reproduction.
4. Synthesis. Our experimental data support observational studies of niche-limit conservatism in non-native plants, which has important implications for their management. Specifically, it suggests that efforts to predict the extent of an invasion based on knowledge of the native niche are likely to be accurate at the level of the species, even if populations undergo genetic changes or respond differently to climatic gradients in the new range.