Nutrient niche differentiation among European herbaceous species reflects an extinction–invasion continuum

Threatened and invasive plant species may appear worlds apart; however, we propose that mechanisms underlying invasive success and extinction risk among European herbaceous species constitute a continuum from successful, well-dispersing, fast-growing species to threatened, slow-growing species. We provide empirical evidence for such an extinction-invasion continuum and show that threatened and naturalized invasive plant species occur at opposite ends. Threatened species persist in phosphorus-limited nutrient-poor habitats, while naturalized and invasive species more often occur in nitrogen-limited nutrient-rich habitats. These opposing niches suggest invasive species do not directly displace threatened species; instead, species replacement and extinction result from nutrient regime shifts. Mitigating and preventing nutrient enrichment, especially phosphorus, for nature conservation protects existing nutrient niches for threatened species and limits plant invasion.