Éradications simultanées du rat noir (Rattus rattus) et des griffes de sorcière (Carpobrotus spp.) sur l’île de Bagaud (parc national de Port-Cros, Provence, France) : résultats préliminaires des conséquences sur les communautés d’arthropodes

Abstract

Simultaneous eradications of Black Rat (Rattus rattus) and Ice plants (Carpobrotus spp.) on Bagaud Island (Port-Cros National Park, Provence, France) : preliminary results on their impacts on Athropods communities. — Biological invasions are recognized as one of the major threats to island biodiversity conservation, and numerous studies have been conducted around the world to restore the biodiversity of islands submitted to invasive species impacts. However, few scientific post-eradication studies were piloted notably for the biodiversity assessment of Arthropod communities. Bagaud Island is an integral reserve of the Port-Cros National Park (PNPC), located in the îles d’Hyères Archipelago (Var, France). In the last centuries, it has undergone two major anthropogenic disturbances : the invasion of the Black Rat (Rattus rattus) and the Ice plants (Carpobrotus spp.), two alien taxa known for their particularly negative effects on the flora and fauna of the Mediterranean island ecosystems, including Arthropods. PNPC has launched a ten-year program of ecological restoration that involves the eradication of these two invasive taxa. The Arthropod communities of the island have been analysed in their initial state in spring 2011, eradications were conducted between September 2011 and January 2013, and the first post-eradication campaign began in spring 2013. The ground fauna was sampled using four transects of Barber traps distributed in different ecological contexts of the island. This first post-eradication study reveals an increase in the abundance of arthropods trapped between 2011 (4868 individuals in 74 traps) and 2013 (6892, n = 60). The average number of trapped Arthropods was significantly higher in areas where Carpobrotus spp. have been eradicated, but declined in the bush area that housed a high density of R. rattus. The communities of decomposers explode, in contrast to predator populations. However, the global specific richness remains stable (220 morphospecies in 2011, 216 in 2013). Scientific monitoring by the PNC must be continued to better determine the direct and indirect long-term impacts of these eradications upon the structure and the functioning of the Arthropods communities of the Bagaud Island.