Using citizen science records from iNaturalist to document geographical range outliers in Australian skinks

Context Accurately describing a species’ geographical distribution is important for informing research and conservation efforts. The citizen science platform iNaturalist provides a valuable resource for increasing our understanding of species distributions. Aims To locate and document geographical range outliers in Australian skinks, and to provide evidence of populations undocumented in the existing literature. Methods We compared observations of Australian skinks on iNaturalist to digital range maps from both the Global Assessment of Reptile Distributions (GARD), the International Union for the Conservation of Nature (IUCN), and a recent Australian reptile field guide. Outlying observations were examined to determine whether they were reliable records. We also made statistical comparisons of the characteristics of species with and without iNaturalist observations and outliers both among species range sizes and subfamilies. Key results In total, 319 (of ~462) native Australian skink species had iNaturalist records. These species generally had larger range sizes, and skink subfamilies were represented unequally. Eighty-two skink species (25.7%) had at least one geographical range outlier, and 33 (10.3%) had at least one novel range outlier, unrecorded anywhere in the scientific literature. Range size did not affect the likelihood of a species to have outliers, but there was still a difference among subfamilies. We found 656 potentially interesting distribution anomalies. Most were not novel, but 111 were novel observations, including potential accidental translocations of a number of species. Most notably, evidence of an established population of Carlia sexdentata in Darwin, Northern Territory. Conclusions Several factors affect how well Australian skink species are represented on iNaturalist, and many species are highly under-represented or unrepresented altogether. Despite this, our method was successful in providing evidence of a number of range anomalies, including some established populations that have not been formally documented. We also showed, through non-novel outliers, that the three map sources used in this study are not always the most accurate source for species distributions in Australian skinks. Implications Our method can potentially be applied to many taxa around the world, so as to increase our understanding of species distributions.