Modelling the Distribution of Three Invasive Freshwater Turtles in Mainland Guadeloupe: Analysis of Their Presence, Abundance and Co-Occurrence

Abstract

The presence of invasive alien species in Caribbean islands is symptomatic of deleterious human impacts on ecosystems. In Guadeloupe, three invasive freshwater turtles (Pelusios castaneus, Trachemys stejnegeri and T. scripta) have been introduced, from colonial times up to the 20th century. However, little information exists on their current distribution and relative abundance. We surveyed 62 undrained sites in Guadeloupe to identify the presence and relative abundance of exotic freshwater turtles from visual observations. We then relied on statistical models to identify factors affecting spatial variation in turtle occupancy (presence/absence) rate and abundance. We found significant positive spatial co-occurrence between the two Trachemys species, suggesting that they tend to select similar habitats and to be active at the same time. In contrast, the spatial distribution of the two Trachemys species appeared to be independent of that of P. castaneus. Model selection indicated that the degree of anthropization around survey sites had contrasting effects on both the presence and abundance of turtles, being positive for Trachemys species and negative for P. castaneus. A comparison with previous reports indicated that Trachemys species have extended their spatial distribution in Guadeloupe and may have become more abundant than P. castaneus. We discuss the relevance of our results to the understanding of the invasion dynamics of exotic turtles and make recommendations for future research.