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Range extension of the ocellated skink, Chalcides ocellatus (Forsskål, 1775), in southern Spain provides a warning on its invasion potential

Abstract:

Early detection of the introduction of alien species is essential for effective management and to avoid potential detrimental effects. The ocellated skink, Chalcides ocellatus (Forsskål, 1775), is a known invasive species. In April 2017, an introduced free-ranging population was found for the first time on the Iberian Peninsula, in Serra del Molar (Alicante). In the last two years, new records have appeared in areas distinct from the first locality. To assess the actual extent of this species’ range, we conducted transects on foot in natural areas and held interviews with country house and plant nursery owners in the spring and summer of 2020. None of the transects in the natural areas found any C. ocellatus, but five confirmed and two probable records were obtained during interviews. These new localities were found between 6.3 and 12.5 km away from the initial locality. At the most distant locality, four country houses were surveyed and very high densities of C. ocellatus (25 skinks in a backyard of 0.2 ha) were found. The respondents agreed that the species started to be sighted around 2017 and 2018 and it is becoming more frequent with every passing year. Although we cannot rule out alternative scenarios, our data about the wide extension of the species and the high densities reached suggest a phase of rapid population expansion. According to guidelines of the allochthonous herpetofauna management in Spain, eradication and active management are strongly recommended before detrimental interactions with native wildlife, such as the endangered Bedriaga’s skink C. bedriagai (Boscá, 1880) being detected. However, the fossorial behaviour of C. ocellatus, and it extending to private areas can make any management efforts extremely difficult. Altogether, this case illustrates the key role of regulating the horticultural trade to avoid biological introductions.