Estrangeira no paraíso: estágio de invasão e contribuições para o manejo de uma palmeira exótica em uma ilha na Floresta Atlântica

Abstract

The number of exotic species with the potential to become invasive has increased in recent decades, with island ecosystems accounting for half of the world areas with occurrences of exotic plants. Islands have high rates of endemism and the invasion of these areas by exotic plants can cause the extinction of native species. Establish programs to prevent and manage alien species on islands should be a priority. The main of this study was to evaluate invasion processes related to the exotic palm Roystonea oleracea on Ilha Grande, RJ, Brazil and provide subsidies to manage the species. More specifically (i) I identified the areas with the presence of the palms and which areas are priority to management; (ii) I evaluated the population dynamics of the palm, analyzing the population growth rates (λ) and which vital rates most impact λ values and; (iii) I identified the vertebrates that interact with the palm fruits and how these vertebrates contribute to the expansion or retraction of the palm on the island. The main trails and inhabited areas on the island were checked and seven areas where the palm occurs were detected. Three of these areas had a high number of palms and were used to population dynamics study. In these areas, I established plots of 40 x 40 m, measured the diameter at ground level (DGL) of all palm individuals, identifying them with numbered aluminum tags and recording their geographic coordinates. From 2015 to 2018 I carried out an annual census in each population and measured the survival (S), growth (G) and fecundity (F) of all individuals. For the calculation of λ and life cycle parameters I used integral projection models (IPMs). Overall, individuals with lower DGL had lower survival or remained in stasis. On the other hand, the individuals with the highest DGL survived more, changed their size and became reproductive. Population growth rates remained stable and around 1 in all populations. S and G of individuals with higher DGL were the vital rates that most impacted the λ. Management actions to remove these individuals in populations are essential to reduce λ. I performed the interaction experiment in the largest population of R. oleracea on the island, randomly selecting 10 adult palms and providing 180 fruits on the ground and a camera trap for each selected palm. I recorded 124 interactions of eight terrestrial vertebrates and the fruits of the palm, most of the animals were rodents and generalist feeding habits. I have identified that the palm is in the final phase of the invasion process, the spread. At this stage the species is considered invasive and management measures should be applied. Although the animals that interact with the fruits are generalists, I recommend gradual management of R. oleracea, replacing it by a native palm species Euterpe edulis. I also recommend that any government decision of management should involve civil society, especially the local residents.