Patterns of land snail diversity over a gradient of habitat degradation: a comparison of three Czech cities

Terrestrial snail faunas were studied at 273 sites in three large Czech cities (Prague, Pilsen and Hradec Králové). The aim was to explore the effect of habitat degradation on land snail diversity in urban environments. Of the 81 species recorded, 12 were considered synanthropic and 29 anthropophobic. We assessed the power of habitat degradation and distance from the city centre as predictors of species richness for: (1) all species combined; (2) synanthropic species alone; and (3) anthropophobic alone. The highest correlation was observed between richness of athropophobic species and habitat degradation (average r = −0.69, P < 0.001), which explained on average 48% of the variation, whereas distance from the city centre explained a negligible amount of independent variation. A similar pattern was found for all species combined; however, the amount of explained variation was lower (10% on average). We found a contrasting pattern for the richness of synanthropic species whose occurrence was mainly and negatively driven by the distance from the city centre. However, the amount of explained variation was very unequal among the cities, being very low in Prague and Pilsen (8%) and quite high in Hradec Králové (36%). In conclusion, the response of local snail assemblages along a gradient of habitat degradation can be generalised as a gradual decline in species richness, especially of rare and anthropophobic species. This reduction was independent of the sites’ position within the city, which highlights the importance of natural habitats for the maintenance of snail diversity in urban environments.