The delayed effects of meteorological changes on the water frogs in Central Italy

In long-lived organisms, the impacts of environmental changes may become evident after time, possibly in future generations. In this study, we attempt to reveal possible delayed effects of meteorological changes on mixed populations of water frogs living in small water bodies located in the Tiber River basin, by using a time-lagged correlation analysis. The analysis shows that the temperature–precipitation pattern induces definite delayed effects, which suggest two potential, possibly co-occurring, explanatory effects: (I) a cumulative and symmetric effect on mortality and (II) a point and asymmetric effect on recruitment. Our data suggest that the water availability in late summer–early autumn affects the survival of tadpoles and migrating frogs, with no differential effect on the parental species Pelophylax bergeri and the hybrid Pelophylax kl. hispanicus, whereas autumn precipitation has a greater impact on the fecundity and/or reproductive success of the parental species. The best time-lagged regression equations between population data and the annual de Martonne aridity index (IDMa) indicate that IDMa\20 mm C-1 is critical for the persistence of the water frogs, and predict that the studied populations will experience a significant decline within the current scenario of climate change.