Effects of invasive species on the ecosystem services of a tropical insular protected area in Brazil

Invasive alien species (IAS) represent a global problem for biodiversity conservation, and a growing concern involving IAS is related to their impacts on ecosystem services. However, their effects on ecosystem services in insular ecosystems are poorly known, which are particularly relevant and concerning due to the fragility and limited resources in these areas for several organisms, including humans. Therefore, the present study aimed to inventory ecosystem services and assess the impact of IAS on these services and the terrestrial ecosystems of the Fernando de Noronha Archipelago, Brazil, which is a tropical protected area. The approach was applied to four IAS: black rat (Rattus rattus), domestic cat (Felis catus), tegu lizard (Salvator merianae), and lead tree (Leucaena leucocephala). A worksheet for ecosystem services was created, using the subdivisions defined in the zoning of the protected areas of Fernando de Noronha as management units, namely Urban Area, Beach Area, Green Area, Primitive Area, and Secondary Island. Additionally, two quantitative approaches were combined: the INvasive Species Effects Assessment Tool (INSEAT) to assess the positive and negative effects of IAS on ecosystem services, based on a questionnaire applied to experts; and the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) software to estimate the risk of impacts from IAS. In total, 21 ecosystem services, 41 benefits, and 10 groups of benefitting social actors were identified in Fernando de Noronha. In general, all IAS presented risks to the ecosystem services of Fernando de Noronha, especially F. catus and R. rattus. According to the impact index, the IAS caused negative effects to most ecosystem services considered, but the effects were more pronounced on the provisioning and cultural ecosystem service groups. On the other hand, a positive effect was found for L. leucocephala on regulating and maintenance services, although with a low impact index. With the exception of the Urban Area, all management units showed a high risk of being impacted by IAS, especially the Primitive Area. The main social actors impacted by the IAS were the local community, the floating population, and the Administration. The present study is the first to combine these quantitative techniques (INSEAT and InVEST) and represents a set of guidelines for ecosystem-based management to mitigate the impact of IAS, aiming at the maintenance and improvement of ecosystem services within protected areas in insular environments.