Patterns of variation in dietary composition among four populations of Alpine salamanders (Salamandra atra prenjensis)

Abstract

In this paper we studied the diet in four allopatric populations of alpine salamanders in the Dinarides (Salamandra atra prenjensis). Food consumption was assessed by stomach flushing while food availability by pitfall traps and netting. We aimed to: (i) assess the realized dietary niche, (ii) investigate prey preferences, (ii) explore individual specialization, clustering and nestedness. All populations have an equally wide dietary span that is among the largest reported for terrestrial salamanders. On the other hand, the amount of ingested prey is rather low compared to other salamander species; the quantity of consumed prey did not differ among populations but younger individuals fed more than adults. Food composition somewhat differed among populations but not among sex/age classes. In all four populations, the bulk of diet consisted of beetles, spiders, snails and millipedes; except for beetles, such prey was also preffered together with centipedes and isopods. For most of the prey categories, the direction of the electivity indices was the same across populations. In none of the populations a nested pattern in the interindividual subdivision of dietary resources was registered. However, indications for individual specialization and modularity were observed disclosing that the broad niche of populations is composed of smaller individual niches that cluster along the dietary axis. Overall, the four populations have very similar structural characteristics of the dietary niche and there is little evidence for local dietary differentiation probably due to the absence of drivers for change.