Altitudinal variation of community metrics in Italian small mammal assemblages as revealed by Barn Owl (Tyto alba) pellets

Abstract

A databank on the pellets of a widespread owl species (the Barn Owl, Tyto alba) was used in order to evaluate the differences in taxonomical composition and community metrics of small mammals (Rodentia and Soricomorpha) along an altitude gradient in Italy. The databank consisted of data from 292 sites, with altitudes ranging between −6 and 1292 m a.s.l. GLM models showed that the number of Rodentia species decreased significantly with elevation gradient, but increased significantly in Soricomorpha. Although there was no overall effect of the altitude on the number of species of Rodentia + Soricomorpha pooled, when we focused only on the central Apennine sites, there was a marginally significant negative correlation between number of species and altitude. There was also a significant increase in abundance with elevation in Soricinae and a significant decrease of abundance with elevation in Crocidurinae. Concerning the smallest sized Soricomorpha, there was a gradual substitution effect of one species (Suncus etruscus) with another (Sorex minutus) with elevation increases, and a logistic regression model revealed that elevation negatively affected the probability of presence of S. etruscus whereas it affected positively that of S. minutus. We think that the decrease in number of species of Rodentia with altitude may depend on the higher rate of agricultural land existing at lower elevations in Italy. The overall pattern of Soricomorpha would depend on the dominance of Soricinae species over the Crocidurinae (in terms of both number of species and relative abundance per site), with the Soricinae being more linked to temperate bioclimates than the Mediterranean-bioclimate-linked Crocidurinae.