Benign Environments do not Explain the Increased Vigour of Non-indigenous Plants: A Cross-continental Transplant Experiment

Abstract

Invasive plants tend to be taller and produce more biomass in their introduced range than conspecifics growing in their native range. Such observations are usually explained by more 'benign' environments, implying that plastic, phenotypic responses are responsible for increased vigour. We compared the growth of 10 Lythrum salicaria populations from indigenous and non-indigenous distributions in two gardens: one located in Europe (indigenous range), the other in North America (non-indigenous range). Spearman rank correlations of different growth variables were generally significant, suggesting that certain genotypes show increased vigour regardless of growing location. More benign climates or the absence of natural enemies are not sufficient to explain this increased vigour. Plant performance tended to be higher in populations from the introduced range, though few differences were statistically significant. To test alternative hypotheses of 'increased vigour' larger sample sizes will be required which was not attempted in this study.