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.

Keywords: Lithuania; berry plantations; meadows; niche width; orchards; small herbivores; voles.

Figure 1

Distribution of sympatric Microtus species at the trapping sites in Lithuania, 2018–2020. Due to small numbers of trapped field and root voles, the proportions of these species do not correspond to the width of slices in the pie charts.

Figure 2

Distribution of syntopic Microtus species according to stable isotope ratios: (a) irrespective of habitat; (b) in control habitats (meadows); and (c) in apple orchards. Sample size is shown in the legend.

Figure 3

Central ellipses of syntopic Microtus species in the isotopic space, representing fundamental niches: (a) irrespective of habitat; (b) in control habitats; and (c) in apple orchards. Sample size is the same, as in Figure 2.

Figure 4

Central position (mean ± SE) of stable isotope ratios of the common vole without or in limited co-occurrence: (a) plum orchards; (b) currant plantations; (c) raspberry plantations. Sample size is shown in the legend.

Figure 5

Intraspecific differences in the stable isotope values in the hair of adult, subadult, and young animals: (a) common vole; (b) field vole; (c) root vole. Sample size is shown in the legend.

Figure 6

Intraspecific differences in the stable isotope values in the hair of males and females: (a) common vole; (b) field vole; (c) root vole. Sample size is shown in the legend.