Food habits of the green lizard, Lacerta bilineata, in central Italy and a reliability test of faecal pellet analysis

Food habits of the green lizard (Lacerta bilineata) were studied in some Mediterranean sites of the vicinities of Rome (Latium, central Italy), by means both of stomach dissection of individuals found already dead in the field and faeces analysis of living individuals. The taxonomic diet composition of the lizards was accurately described by both methods, thus demonstrating the reliability of faecal pellet analysis as an non-cruel method to study lizard diets. However, by using the faeces analysis technique, it is difficult to measure the exact food intake rate (items / unit of time) as well as the size distribution of prey ingested by lizards. There was a remarkable ontogenetic change in the taxonomic diet composition of green lizards: adults essentially consumed beetles and isopods, whereas juveniles fed mainly upon orthopterans, spiders, and Rhynchota. Cannibalism and predation upon small vertebrates (lizards) were very rare events. It is suggested that (i) age-related differences in microhabitat frequented could explain the dietary differences between young and adult lizards due to different availability of the various prey categories in the various microhabitats, and that (ii) adults and juveniles partition their habitats to reduce intraspecific interference competition.