The rarest invaders: systematic global evidence for the conservation-invasion paradox in plants.

Abstract

The Conservation-Invasion Paradox (CIP) refers to species that are threatened or declining within their native ranges establish invasive populations elsewhere. While this paradox has been documented primarily in animals, its prevalence, structure, and drivers in plants remain poorly understood. Investigating the CIP is crucial for linking mechanisms that underlie both species decline and invasion success, and offers insights into biodiversity change in the Anthropocene. Here, we provide the first global, systematic assessment of the CIP in vascular plants by integrating three global alien flora databases with three conservation assessment databases. Using reproducible cross-database criteria (the simultaneous occurrence of invasive status in at least one global alien flora database and conservation concern in at least one global conservation assessment database), we identified 89 plant species under the CIP. Threatened plant species were approximately 10 times less likely to naturalize and 17 times less likely to become invasive than non-threatened species, making the CIP a genuinely paradoxical outcome. CIP plant species are concentrated in the Americas and East-Southeast Asia and exhibit strong anthropogenic signals, with dominant human uses and persistent threats from agriculture, overexploitation, and development. Our findings demonstrate that the CIP arises from a spatial decoupling between invasion success and native range persistence, driven by the same human valuation processes that promotes translocation and intensify native-range pressures. The CIP also exposes a mismatch between biological invasion and conservation frameworks, where separate regulatory systems independently assess invasive status and conservation concern, revealing a governance gap for species exhibiting both conditions simultaneously.