Oribatid (Acari: Oribatida) diversity in natural and altered open arid ecosystems of South-Eastern Caucasus

Oribatid mite diversity was investigated in the most understudied region of Georgian South-Eastern Caucasus - open arid ecosystems, which are under heavy natural and anthropogenic disturbance. Field sampling was performed in three geographical units and in each unit three types of ecosystems with different disturbance classes were studied: (1) Arable lands with severe (ASE) and moderate (AME) erosion; (2) Pastures with heavy (PH) and moderate (PM) overgrazing; (3) Natural grassland with severe (NSE), medium (NME) and no (N) erosion. Eighty species of oribatid mites were identified in total. Total raw richness of species was highest in natural grassland (68 species), followed by arable lands with medium erosion (50 species), natural grassland with medium erosion (44 species), pastures with medium erosion (41 species), overgrazed pastures (36 species), arable lands with severe erosion (35) and grassland with severe erosion (31 species). Non-parametric estimation of species richness showed 80 % of per-site sampling completeness on average. Similar to species richness, average individual density was also highest in natural sites (5500 in./m2) and lowest - in grassland with severe erosion (500 in./ m2). Indicator Species Analyses (ISA) and regression analyses showed that the natural undisturbed sites displayed largest number of potential indicator species most of which are absent from disturbed sites. Natural grasslands are characterized by on average seven species (Ceratoppia quadridentata (Haller, 1882), Eremulus flagellifer Berlese, 1908, Oribatella berlesei (Michael, 1898), Oribatula interrupta (Willmann, 1939), Xenillus tegeocranus (Hermann, 1804), Metabelba papillipes (Nicolet, 1855), Striatoppia weigmanni Murvanidze & Behan-Pelletier, 2011) with high indicator value (i.e. specificity >0.9) irrespective the sampling season. No other oribatid species were found to be good indicators of other disturbance classes.