Naturalized and Invasive Species Integrate Differently in the Trait Space of Local Plant Communities

How alien plant species integrate into local native communities remains a widely debated but largely unresolved question. For 12,460 plant communities from six different habitats, we show that naturalized non-invasive species integrate near the center of the multidimensional functional trait space of each community, whereas invasive species tend to occupy the edges. This pattern is driven mainly by specific leaf area, plant height and seed mass, followed by genome size. These results suggest that functional similarity to resident native species supports successful naturalization of alien species through preadaptation to environmental conditions. In contrast, the functional dissimilarity of invasive species enables them to exploit new niches, potentially avoiding direct competition with co-occurring native species while still passing through environmental filters. The magnitude of differences between native, naturalized and invasive species is habitat-specific, reflecting both the local ecological conditions and the traits of the most widespread species in a given habitat.