Risk of invasion by frequently traded freshwater turtles

Risk assessment allows the identification of non-native species most likely to become invasive and cause harm, and helps to set up preventive measures such as trade regulations. Freshwater turtles are among the most traded pets; an increasing number of species are easily available and frequently released by owners in natural wetlands. This study identified a pool of freshwater turtles frequently traded at cheap prices, and performed risk assessment at multiple steps of the invasion process. Establishment risk was assessed through species distribution models (MaxEnt and Boosted Regression Trees) based on global presence records and bioclimatic variables. We also analyzed ecological and life history traits favouring release, establishment and population growth. Besides the already invasive Trachemys scripta, at least 14 species are easily found in the pet market. For most of them, species distribution models identified areas with suitable climate outside the native range. Validation with independent data confirmed the reliability of the modelling approach. Pelodiscus sinensis and Pelomedusa subrufa had the broadest areas of suitable climate outside the native range. For all the species, possibility of coexistence with humans and reproductive traits suggest high risk of invasion, if introduced in areas with suitable climate. The availability of spatially explicit maps of risk allows to identify areas where preventive measures are urgently needed. In Europe, an expansion of trade regulations is needed to avoid that multiple freshwater turtles become invasive.