Abstract
Mountain scree habitats are intermediate habitats between the base of the soil and the bedrock. They are composed of a network of small cracks and voids, and are commonly situated at the lower levels of scree slopes. Their environment is defined by empty spaces inside the scree, the absence of light and photoperiod, low temperature, and resource poor conditions. Soil arthropod communities, their trophic structure as well as their use of basal resources in mountain scree are little studied despite the fact that they are important components of these systems. Here, we investigate stable isotope ratios (15N/14N, 13C/12C) of oribatid mites (Oribatida, Acari) to understand their trophic niches and their variation with depth (50 and 75 cm) at two mountain scree sites (Cerdacul Stanciului, Marele Grohotis) in the Romanian Carpathians. Further, we used existing data to investigate the reproductive mode of the species in that habitat, as this may be related to resource availability. We hypothesized that trophic niches of oribatid mites will not differ between the two mountain scree regions but will be affected by depth. We furthermore hypothesized that due to the resource poor conditions oribatid mite species will span a narrow range of trophic levels, and that species are sexual rather than parthenogenetic. Our results showed that (1) oribatid mite trophic structure only slightly differed between the two sites indicating that the trophic ecology of oribatid mites in scree habitats is consistent and predictable, (2) oribatid mite trophic structure did not differ between the two studied soil depths indicating that the structure and availability of resources that were used by oribatid mites in deeper scree habitats varies little with depth, (3) oribatid mite species spanned only three trophic levels indicating that the habitat is rather resource poor, and (4) that all studied oribatid mite species were sexual supporting the view that resource poor conditions favour sexual reproduction.
Highlights
Mountain scree habitats are commonly found in scree slopes, where soil has not filled in the spaces
Twelve oribatid mite species exclusively occurred at the Marele Grohotis site (Table 1), whereas no oribatid mite species occurred exclusively at the Cerdacul Stanciului site; five oribatid mite species occurred at both sites (Ceratoppia bipilis, Chamobates cuspidatus, Oribatella calcarata, Oribatella foliata and Oribatella quadricornuta); only two species (C. bipilis and O. foliata) occurred at both sites in sufficient numbers for statistical analyses
Only two species (O. foliata and C. bipilis) occurred in sufficient numbers to allow at least two stable isotope measurements per site. 15N and 13C values of O. foliata did not differ significantly between ‘Cerdacul Stanciului’ and ‘Marele Grohotis’ (DFA: Wilks’ λ = 0.14; approx. F2,2 = 5.94, p = 0.14), whereas those of C. bipilis differed significantly between dthifefetrweoncseistesin(D13FCA(:AWNiOlkVs’Aλ: =F 10,8.1 =3 ;40a.p9p,ropx
Summary
Mountain scree habitats are commonly found in scree slopes, where soil has not filled in the spaces. The method provides integrative insight into the trophic position of consumers and into the use of basal resources in soil animal communities (Scheu and Falca 2000; Tiunov 2007; Maraun et al 2011; Potapov et al 2019). Fractionation of 13C is lower, averaging ~ 0.4 δ units per trophic level (Post 2002; Martinez del Rio et al 2009), and is of little use to determine the trophic structure of communities (Ponsard and Arditi 2000); in particular in soil it allows to trace the use of basal resources of consumers (Albers et al 2006; Pollierer et al 2009; Melguizo-Ruiz et al 2017; Potapov et al 2019). We hypothesized that (4) the reproductive mode of oribatid mites in mountain scree is mainly sexual, as resource poor habitats are assumed to be dominated by sexual species
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