Isotopic Niche of Syntopic Granivores in Commercial Orchards and Meadows

SIMPLE SUMMARY: Granivorous murids, namely striped field (Apodemus agrarius), yellow-necked (Apodemus flavicollis), and harvest (Micromys minutus) mice, occur in a variety of habitats and live syntopically in agricultural areas. Agroecosystems may be quite complex isotopically with δ(15)N values being influenced by many internal and external fluxes. Using isotopic (δ(15)N and δ(13)C) compositions from hair samples, we analysed isotopic niches of granivores in apple and plum orchards, raspberry and currant plantations, and nearby meadows in Lithuania. As the main hypothesis, we expected differences in the isotopic niches of these species (being a proxy for their diet), minimising interspecific competition. Striped field and yellow-necked mice were trapped in every habitat. Therefore, syntopic co-occurrence of granivores depended on the presence of harvest mice in the apple orchards, raspberry plantations, and meadows that served as control habitats. All species were fully separated according to δ(15)N values, presuming different amounts of food of animal origin in their diet. The separation of species according to δ(13)C was not expressed in all habitats. The core dietary niches of these species were fully separated in the apple orchards and raspberry plantations. Intraspecific differences of the isotopic niche were not present in any of the three species: that is, resources were equally used by males and females, adults, subadults, and juveniles. ABSTRACT: In agricultural habitats, diets and trophic positions of syntopic granivorous small mammals are not known sufficiently. Agroecosystems may be quite complex isotopically and the most complex situation concerns the nitrogen-15 isotope as δ(15)N values are influenced by many internal and external fluxes. We analysed the isotopic niches of striped field (Apodemus agrarius), yellow-necked (Apodemus flavicollis), and harvest (Micromys minutus) mice living sympatrically and syntopically in apple and plum orchards, raspberry and currant plantations, and nearby meadows that were used as control habitats. Carbon (δ(13)C) and nitrogen (δ(15)N) stable isotope ratios from hair samples were used as a proxy for their diet. As the main hypothesis, we expected differences in the isotopic niches of these three species, minimising interspecific competition. All species were fully separated according to δ(15)N values, presuming different amounts of food of animal origin in their diet. The separation of species according to δ(13)C was not expressed in all habitats. The core dietary niches of these species were fully separated in the apple orchards and raspberry plantations. Intraspecific differences of the isotopic niche were not present in any of the three species: that is, resources were equally used by males and females, adults, subadults, and juveniles.