Stable Isotopes Reveal the Dominant Species to Have the Widest Trophic Niche of Three Syntopic Microtus Voles

Abstract

Diets and trophic positions of co-occurring animals are fundamental issues in their ecology, and these issues in syntopic rodents have been studied insufficiently. Using carbon (δ13C) and nitrogen (δ15N) stable isotope ratios from hair samples, we analysed the trophic niches of common (Microtus arvalis), field (M. agrestis), and root (M. oeconomus) voles co-occurring in orchards, berry plantations, and nearby meadows (as control habitat to orchards and plantations). We tested if the niche of the dominant common vole was the widest, whether its width depended on the presence of other vole species, and whether there were intraspecific differences. Results suggest stability in the trophic niches of all three Microtus species, as season explained only 2% of the variance. The widest trophic niche was a characteristic of the dominant common vole, the range of δ13C values exceeding the other two species by 1.6, the range of δ15N values exceeding the other two species by 1.9, and the total area of niche exceeding that of the other voles by 2.3–3 times. In the meadows and apple orchards, co-occurring vole species were separated according to δ13C (highest values in the dominant common vole), but they maintained similar δ15N values. Results give new insights into the trophic ecology small herbivores, showing the impact of species co-occurrence.

Isotopic Niche of Syntopic Granivores in Commercial Orchards and Meadows

“…This conforms to the hypothesis that species coexistence should be ensured by the partitioning of resources in space and time if they compete for this resource [ 25 ]. The hypothesis was also confirmed for rodents in Africa [ 44 , 48 ], for a flooded meadow in Lithuania [ 9 ], and for sympatric/syntopic voles of the genus Microtus in Lithuania [ 23 ]. The co-occurrence of species using similar resources has an influence on the trophic niche width and the partitioning of resources [ 36 , 37 , 38 , 46 , 48 ].…”

“…Resource-sharing is not easy to investigate; therefore, stable carbon and nitrogen isotopes in the tissues or hair of rodents may be used as a proxy, representing the diet of the individual and the trophic niche of the species [ 44 ]. Used at the level of animal communities, stable isotope analysis may show not only the dimensions of the trophic niche (e.g., niche width), but also the resource partitioning [ 9 , 23 , 45 , 46 ]. Therefore, as mentioned by Post, “stable isotope techniques combine benefits of both the trophic-level and food web paradigms in food web ecology” [ 47 ].…”

“…Two granivore species, namely M. minutus and A. agrarius, were not separated in flooded meadows in which resources were abundant for most of the small mammal species from the four guilds-granivores, omnivores, herbivores, and omnivores [ 9 ]. From the perspective of co-occurrence, the syntopy of granivores was less expressed than that in herbivore species in the commercial gardens and orchards [ 23 , 31 ]. Therefore, we should presume that these agricultural habitats are richer in resources for herbivores.…”

“…In commercial orchards and berry plantations in Lithuania, the dominant species is the common vole ( Microtus arvalis ), while A. agrarius and A. flavicollis are subdominants, although they dominate in some cases [ 23 ]. M. minutus is a rare species in commercial gardens, represented by just a few individuals [ 10 ].…”

“…In recent years, diet has been analysed by modern tools such as DNA, fatty acid, or stable isotope analyses [ 34 , 35 , 36 , 37 ]. We used stable carbon and nitrogen ( δ 13 C and δ 15 N) isotope analysis as a reliable tool to investigate the trophic ecology of vertebrate animals including various rodent species [ 9 , 23 , 30 , 36 , 37 , 38 , 39 ].…”