Seasonal variation in the trophic niche in a heterochronic population of Mesotriton alpestris apuanus (Amphibia, Salamandridae) from the south-western Alps

The aim of this study was to analyse the diet composition and feeding strategy of a heterochronic population of the Alpine newt, Triturus alpestris apuanus (Bonaparte, 1839), in a high-altitude pond in the south-western Alps, characterized by a reduced aquatic habitat and low environmental heterogeneity. The co-existence of both adult newt morphs in such a non-complex habitat with short suitable hydroperiod (water surface free of ice) may not be governed by different microhabitat selection or temporal activity, but could be due to diet composition differentiation among morphs. The diet of the newt was examined and compared with prey availability in summer and autumn. Both numerical and volumetric analyses of the gut contents showed that: 1) metamorphs represented a homogeneous group clearly linked to epineustonic prey categories (exogenous arthropods), whereas paedomorphs showed a prey selection mainly towards planktonic food categories; 2) evident seasonal variations in diet composition not connected to aquatic prey availability were observed in the studied forms; 3) metamorphs and paedomorphs may possibly avoid competition (if there is any) through food resource partitioning rather than microhabitat selection.