dataset_ecol and evol

While invasive success of alien plant species is often attributed to their superior competitive abilities, it is also suggested that competitive ability depends on the target species of competition and resource availability. In addition, it remains unclear whether invaders and natives exhibit distinctive intraspecific competitive intensities. This study aimed to evaluate the competitive ability of a successful invader, Lactuca serriola, through a combination of field surveys and a growth chamber experiment. First, we assessed biodiversity and the biomass of native plants in both L. serriola-invaded and uninvaded plots across nine sites. Subsequently, a pairwise competition experiment was conducted between L. serriola and three native weedy plant species commonly found in the invaded plots, under differential nutrient levels. Diversity indices of plant communities and the biomass of most natives showed no significant difference between invaded and uninvaded plots. L. serriola reduced the biomass of the tested natives, but natives also decreased L. serriola biomass when grown together. The intensity of interspecific competition was comparable between L. serriola and natives across nutrient treatments. Notably, intraspecific competition of L. serriola was weaker than that of natives, particularly manifest in the high-nutrient treatment. The results of both field and growth-chamber studies demonstrated that L. serriola was not a particularly strong competitor compared to its neighboring native weedy plants. Its successful invasion can be partially attributed to its weak intraspecific competition intensity, which potentially facilitate successful establishment with high density.