Vanishing herpetofauna: 30 years of species relaxation in a wetland remnant of the Po plain (Northern Italy)

An analysis of a 30-year dataset (1985–2014) concerning a herpetofauna assemblage studied in a site of conservation concern (Northern Italy) is reported with the aim of evidencing a trend in species richness which may reveal the most sensitive ones (i.e., the first to go extinct locally). Our results point to a progressive loss of species (nested species relaxation) which were not replaced over the study period and consequently to a decline in species richness. Among the amphibians, two thresholds in mean species richness were evident in the mid and late 1990s, respectively, whereas reptiles showed a significant threshold only at the end of the 1990s. An inductive hypothesis to explain the abrupt relaxation in species richness in the mid and late 1990s may involve a combination of “pulse” or “press” perturbations at different scales. Moreover, although our long-term standardized study suffers from some limitations, our data clearly indicate a different species-specific sensitivity which could be useful to identify focal species of conservation concern. However, further comparisons with data set collected from long-term and wide-ranging studies are needed to confirm our temporal thresholds, in order to infer a more general model from this local pattern.