From Least Concerned to Endangered? An integrated approach to determine the distribution, suitable habitat and future of Dryophytes immaculatus

Background The immaculate treefrogs, Dryophytes immaculatus , were reported to be abundant in the plains of southern Jiangsu, China, until the 1980s. However, the species has only scarcely been seen since the beginning of the century. Results First, we conducted surveys between 2017 and 2024 at more than 6000 independent sites to determine the occurrence of the species, conducted citizen science surveys resulting in more than 1300 entries to determine the occurrence of the species, and questioned farmers, when possible, about the presence of the species. We detected Dryophytes immaculatus at 207 independent sites, managed to confirm the presence of the species at an additional 11 independent sites based on citizen science data and confirmed its local extinction at eight additional sites. Next, based on the accumulated data, we developed a suite of ecological models, including some with putative absence, to determine the current suitable habitat for D. immaculatus. Finally, we also built ecological models based on climate change scenarios. The ecological models confirmed the habitat to be suitable in an area marginally broader than the one where the species was found, and the climate change scenarios highlighted a shift in the location of the suitable habitat for all scenarios and time periods tested, with a weak overlap with the current distribution of the species. Based on the data accumulated, we could also follow the categories and criteria of the IUCN Red List of Threatened Species and we suggested for the species to be listed as Endangered under both criteria B2ab(i,ii,iii,v) based on geographic range, and C2a(i) based on the small and declining population size. Conclusion The range of D. immaculatus has contracted over the last decades, at a speed high enough for people sharing their land with the species to remember them, and the habitat suitable for the species is further declining, and predicted to entirely collapse in all future climatic scenarios. While not Critically Endangered yet, D. immaculatus is in need of conservation actions, especially to prevent future decline in habitat quality.