Biodiversity of Terrestrial Gastropods in Two Urban Ecological Reserves in Argentina

Urban ecological reserves in Buenos Aires city (Argentina) were intended as spaces for outdoor recreation, preservation of natural environments and protection of native species. Reserva Ecológica Costanera Sur (RECS) and Reserva Ecológica Ciudad Universitaria Costanera Norte (RECUCN) are located on the right bank of the Río de la Plata estuary. In view of the repeated appearance of non-native land snails and slugs in Argentina during the last four decades, we wanted to know to what extent the terrestrial gastropod faunas of these two reserves were composed of native or non-native species. As RECS is larger than RECUCN, we also tested the hypothesis that abundance, species richness and diversity would be higher in the former than in the latter. Fifty-two and 25 sites were sampled for terrestrial snails and slugs in RECS and RECUCN, respectively. Land gastropod species richness was similar in RECS (14 species) and RECUCN (12 species). Non-native gastropods were much more diverse and overwhelmingly more abundant than native ones. The terrestrial gastropod fauna is dominated by non-native snails and slugs (98.4% non-native individuals vs. 1.6% native in RECS, 97.5% vs. 2.5% in RECUCN), most of them never previously reported from these reserves. More than 78% of the individuals found in RECUCN belonged to the non-native snail Vallonia pulchella, which was the species that most contributed to the dissimilarity between reserves. This study shows that so far, urban ecological reserves in Buenos Aires city are sites where mainly exotic rather than native terrestrial molluscs are being preserved. The dominance of nonnative species in these urban ecological reserves endorses the pervasive advance of synanthropic species in urban land snail assemblages already documented for other biogeographic regions.