Variations in trophic niches of soil microarthropods with elevation in two distant mountain regions in Eurasia as indicated by stable isotopes (15N, 13C)

Abstract

Knowledge on the trophic niche of animal species is important for understanding their coexistence and hence animal diversity. Trophic niches have been shown to vary with environmental conditions, but consequences of trophic niche shifts for food-web structure and functioning are little studied and this applies in particular for belowground communities. Here, using stable isotopes (15N, 13C), we investigated shifts in trophic niches of oribatid mites as model soil animal taxon along elevational gradients of two mountain ranges in Eurasia, the Alps in Austria and Changbai Mountain in China. The results showed pronounced differences in the use of basal resources (Δ13C values) and trophic positions (Δ15N values) between the two mountains due to the different parent rock with calcareous soils in the Alps and basalt bedrock on Changbai Mountain. Further, trophic positions changed with altitude, primarily related to changes in litter quality. Differences in trophic niches of oribatid mites between the two mountains were related to differences in functional traits such as body mass and reproductive mode. Generally, stable isotope values closely correlated with body mass underlining the importance of morphological characteristics as well as the parent rock for variations in trophic niches. Moreover, stable isotope values differed between parthenogenetic and sexual species, but this depended on mountain and parent rock, with higher trophic plasticity in parthenogenetic species on Changbai Mountain than in the Alps. Overall, our findings highlight the decisive role of parent rock in structuring montane soil food webs and provide novel insight into factors responsible for shifts in trophic niches in soil invertebrates.