Variability of Seasonal Trophic Niche in Two Sympatric Salamanders: Italian Cave Salamanders and Fire Salamanders

The trophic niche is one of the most important ecological traits for any species, providing information about trophic position in the food web, habitat preferences, and interspecific interactions. In this study, we describe the autumn diet of two sympatric species of salamander from central Italy—Italian Cave Salamanders (Speleomantes italicus) and Fire Salamanders (Salamandra salamandra), assessing whether competition for the same prey occurs. Furthermore, we combine our data with those obtained for the same population during a different season (spring) and assess potential seasonal variation in the diet of these two salamander species. The overlap of the trophic niche between the two species was limited, with S. italicus consuming smaller and fast-moving prey (e.g., Diptera, Collembola), and S. salamandra consuming slow and often elongated prey (e.g., Gastropoda, Haplotaxida, Diplopoda). Seasonal differences in diet composition were observed in both species between spring and autumn; in autumn, both species narrowed their trophic niche breadth. This seasonal divergence is likely due to the variation of prey phenology and availability. The consumption of prey of different size was likely the main factor allowing the coexistence of these two salamander species. In both species we observed a general increase in the proportion of generalist individuals in autumn, most likely because of a reduction in prey availability. In addition to providing information on the trophic niche of these species, our study represented a further step that helps unravel the dynamics promoting the coexistence of potentially competing species.