Differential vulnerability to biological invasions: not all protected areas (and not all invaders) are the same

Abstract

Protected areas (PAs) are fundamental for global biodiversity conservation but many are not delivering their conservation potential. In particular, the European Natura 2000 (N2K)–the largest coordinated network of PAs in the world—has insofar proved insufficient to achieve the EU’s biodiversity conservation targets. Despite the adoption of innovative legislation on the prevention and management of biological invasions, invasive alien species (IAS) remain a main threat to N2K. We explored whether the regulatory status of N2K has been efficient to prevent the establishment of regulated IAS (those under the scope of EU or national regulations) by conducting a case study in a highly biodiverse Mediterranean region of Spain. We: (1) analyzed whether the number of both regulated and unregulated IAS differ across adjacent unprotected areas (belt zones), N2K sites and N2K sites with additional protection as national park or nature reserve (APAs); (2) compared the spread pathways of regulated IAS present in areas with different protection status. While APAs hosted fewer regulated IAS, N2K sites did not perform better than belt zones. Specifically, there were fewer regulated IAS that spread through natural dispersal or intentional human assistance in APAs compared to N2K and belt zones, but those dispersing with unintentional human assistance were similarly distributed in PAs and belt zones. Further, protection level did not reduce the number of unregulated IAS. Thus, observed patterns indicate that the conservation obligations bound to the designation of an area as an N2K site are not sufficient to prevent or slow down biological invasions.