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.

山卵石生境是土壤基础和基岩之间的中间生境。它们由小裂缝和空隙组成，通常位于卵石坡度较低的位置。它们的环境是由卵石内部的空白空间，没有光照和光周期，温度低以及资源贫乏的条件所定义的。尽管土壤节肢动物群落，它们的营养结构以及在山卵石中基础资源的利用很少受到研究，尽管它们是这些系统的重要组成部分。在这里，我们研究稳定的同位素比（¹⁵ N / ¹⁴ N，¹³ C / ¹²C）oribatid螨（Oribatida，Acari）了解它们在罗马尼亚喀尔巴阡山脉的两个山卵石场（Cerdacul Stanciului，Marele Grohotis）的营养位及其随深度（50和75 cm）的变化。此外，我们使用现有数据来调查该栖息地中物种的繁殖方式，因为这可能与资源的可获得性有关。我们假设，在两个山卵石区域之间，鸟龟螨的营养位不会有所不同，但会受到深度的影响。我们进一步假设，由于资源条件恶劣，oribatid螨物种的营养水平范围很窄，并且该物种是有性的而不是孤雌生殖的。