Non-invasive invaders from the Caribbean: the status of Johnstone's Whistling frog (Eleutherodactylus johnstonei) ten years after its introduction to Western French Guiana

The neotropical frog Eleutherodactylus johnstonei (Anura: Eleutherodactylidae) has been referred to as a highly invasive species on grounds of its wide distribution and is expected to extend its range significantly based on recent climate model assumptions. The frog was introduced to a number of South American mainland localities, including French Guiana. Other species of the genus have become invasive on oceanic islands such as Hawaii where they pose serious biological and economical problems. No data are available on the invasion status of E. johnstonei populations from coastal South America. Here we present the first assessment of the status of a mainland population from French Guiana 10 years after the introduction of the species. We found that the species has not spread significantly within the last ten years and so far does not exhibit a high invasion potential. Frogs were restricted to urban garden habitats showing significantly higher abundance in gardens containing ornamental potted plants. Distribution patterns were best explained by two dispersal-related factors operating at different scales: (1) distance of occupied sites to nearest population indicating short-distance active dispersal using stepping stone habitats, and (2) distance of occupied sites to shore with a distinct bimodal pattern indicating long-distance passive or jump-dispersal, most likely due to the exchange or transfer of ornamental plants. Even though past and current invasion potential can be considered low, we advocate the implementation of a regional monitoring scheme and detailed studies on biotic interactions with native fauna.