Evolution of invasiveness through increased resource use in a vacant niche

Non-native plants are now a pervasive feature of ecosystems across the globe¹. One hypothesis for this pattern is that introduced species occupy open niches in recipient communities^2,3. If true, then non-native plants should often benefit from low competition for limiting resources that define niches. Many plants have evolved larger size after introduction, consistent with increased access to limiting resources^4-9. It has been difficult to test whether larger size reflects adaptation to exploit open resources, however, because vacant niches are generally challenging to identify in plants. Here we take advantage of a situation in which a highly invasive non-native plant, Centaurea solstitialis L. (yellow starthistle, hereafter 'YST'), occupies a well-described environmental niche, wherein water is a known limiting resource^10,11. We use a glasshouse common environment and climatic niche modeling to reveal that invading YST has evolved a higher-fitness life history at the expense of increased dependence on water. Critically, historical declines in resident competitors have made water more available for introduced plants^11,12, demonstrating how native biodiversity declines can open niches and create opportunities for introduced species to evolve increased resource use, a potentially widespread basis for introduction success and the evolution of invasive life histories.