Reproductive Ecology of Endangered Amphibians

Abstract

Amphibian populations across Europe and the Mediterranean basin are declining at unprecedented rates, with reproductive failure constituting the primary proximate driver of population collapse in climatically stressed habitats. This study characterised the reproductive ecology of 14 endangered amphibian species (6 anurans, 5 caudates, 3 caecilians) across 42 breeding wetlands in Italy, Switzerland, and southern France, integrating: (i) multi-year clutch census data (2016-2023) from 12,840 individually marked breeding adults at 42 sites; (ii) hatching success measurements from 3,864 clutches across habitat quality gradients; and (iii) larval survival tracking through metamorphosis for 8,240 larvae across 28 sites. Mean breeding phenology advanced by 6.8 +/- 1.4 days per decade, strongly correlated with February-March mean temperature (r = -0.74, p < 0.001). Clutch size declined significantly with increasing water temperature at oviposition (beta = -1.84 eggs/degC, p < 0.001) and pond desiccation risk (beta = -3.12 eggs/unit, p < 0.001). Hatching success ranged from 31.4% in degraded agricultural ponds to 87.6% in high-quality reference wetlands, with pH, conductivity, and emergent vegetation cover explaining 68% of variance in a generalised linear model. Larval survival to metamorphosis was most strongly predicted by hydroperiod reliability (r = +0.71, p < 0.001) and the absence of introduced predatory fish (OR = 3.84, p < 0.001). A Reproductive Vulnerability Index (RVI) integrating five reproductive traits predicted population trend direction with 81.4% accuracy. These findings identify hydroperiod stability and invasive predator exclusion as the highest-priority management interventions to safeguard endangered amphibian reproduction under accelerating Mediterranean climate change.