Annotated checklist of Georgian oribatid mites-II.

The checklist of oribatid mites from Georgia is updated using sampling data from more than 230 locations during field works conducted between 2016 and 2022. We report 32 species of oribatid mites, sixteen of them were collected between 2017 and 2019, six were missing in Checklist I, while eleven species are new records for the country. The genus Ameronothrus was found in Georgia for the first time, but could not be identified to species level. Additional information about the distribution of Epilohmannia styriaca Schuster, 1960, Sphaerozetes orbicularis (C.L. Koch, 1835) and Fuscozetes fuscipes (C.L. Koch, 1844) is given. For each species we provide notes about regional and global distribution as well as information about their ecology. This list brings the number of identified species known for Georgia up to 563.

Land use and soil characteristics affect soil organisms differently from above-ground assemblages.

BACKGROUND: Land-use is a major driver of changes in biodiversity worldwide, but studies have overwhelmingly focused on above-ground taxa: the effects on soil biodiversity are less well known, despite the importance of soil organisms in ecosystem functioning. We modelled data from a global biodiversity database to compare how the abundance of soil-dwelling and above-ground organisms responded to land use and soil properties. RESULTS: We found that land use affects overall abundance differently in soil and above-ground assemblages. The abundance of soil organisms was markedly lower in cropland and plantation habitats than in primary vegetation and pasture. Soil properties influenced the abundance of soil biota in ways that differed among land uses, suggesting they shape both abundance and its response to land use. CONCLUSIONS: Our results caution against assuming models or indicators derived from above-ground data can apply to soil assemblages and highlight the potential value of incorporating soil properties into biodiversity models.

Parthenogenetic vs. sexual reproduction in oribatid mite communities.

The dominance of sex in Metazoa is enigmatic. Sexual species allocate resources to the production of males, while potentially facing negative effects such as the loss of well-adapted genotypes due to recombination, and exposure to diseases and predators during mating. Two major hypotheses have been put forward to explain the advantages of parthenogenetic versus sexual reproduction in animals, that is, the Red Queen hypothesis and the Tangled Bank/Structured Resource Theory of Sex. The Red Queen hypothesis assumes that antagonistic predator-prey/ parasite-host interactions favor sex. The Structured Resource Theory of Sex predicts sexual reproduction to be favored if resources are in short supply and aggregated in space. In soil, a remarkable number of invertebrates reproduce by parthenogenesis, and this pattern is most pronounced in oribatid mites (Oribatida, Acari). Oribatid mites are abundant in virtually any soil across very different habitats, and include many sexual and parthenogenetic (thelytokous) species. Thereby, they represent an ideal model group to investigate the role of sexual versus parthenogenetic reproduction across different ecosystems and habitats. Here, we compiled data on oribatid mite communities from different ecosystems and habitats across biomes, including tropical rainforests, temperate forests, grasslands, arable fields, salt marshes, bogs, caves, and deadwood. Based on the compiled dataset, we analyzed if the percentage of parthenogenetic species and the percentage of individuals of parthenogenetic species are related to total oribatid mite density, species number, and other potential driving factors of the reproductive mode including altitude and latitude. We then interpret the results in support of either the Red Queen hypothesis or the Structured Resource Theory of Sex. Overall, the data showed that low density of oribatid mites due to harsh environmental conditions is associated with high frequency of parthenogenesis supporting predictions of the Structured Resource Theory of Sex rather than the Red Queen hypothesis.

Patterns of oribatid mite species diversity: testing the effects of elevation, area and sampling effort.

Elevational gradients in species diversity and species area relationships are two well established patterns that are not mutually exclusive in space and time. Elevation and area are both considered as good proxies to detect and characterize the patterns of species diversity distribution. However, such studies are hampered by the incomplete biodiversity data available for ecologists, which may affect the pattern perceptions. Using the large dataset of oribatid mite communities sampled in Georgia, we tested the effects of altitude and area on species distribution using various approaches, while explicitly considering the biases from sampling effort. Our results showed that elevation and area are strongly correlated (with increasing absolute elevation, land area decreases) and both have strong linear effects on species diversity distribution when studied separately. Approaches based on multiple regression and direct removal of co-varied factors, indicated that the effect of area can actually override the effect of elevation in describing the oribatid species diversity distribution along with elevation. On the other hand, the bias of sampling proved significant in perception of elevational species richness pattern with less effect on elevational species area relationship. We suggest that the sampling alone may be responsible for patterns observed and thus should be considered in ecological studies when eligible.

Annotated checklist of Georgian oribatid mites.

A new updated checklist of Georgian oribatid mites is based on the critical review of existing literature data and new findings. The list includes 534 oribatid species of which 21 species are new for the country recorded from more than 390 locations. For each species information of the global and regional distribution is presented with notes on ecological characteristics. As far as necessary we provide remarks on taxonomic issues to overcome the ambiguities and inconsistencies existing in literature.

Oribatid mite communities along an elevational gradient in Sairme gorge (Caucasus).

Many aboveground animals and plant communities have been studied along elevational gradients whereas studies on soil animals are scarce. Here, we studied oribatid mite community distribution along an elevational gradient from 600 to 2200 m in forest ecosystems of the Western Lesser Caucasus Mountains in Georgia. Overall, 86 oribatid mite species were found at the study sites. Oribatid mite densities were generally low (~9800 ind./m(2)), and 74% of all species reproduced sexually indicating that resource conditions at the study sites are generally poor. Oribatids mainly comprised Brachypylina (76%), Mixonomata (13%), Desmonomata (6%) and Enarthronota (5%). Oribatid mite community structure changed along the elevational gradient and the changes correlated with temperature, pH, litter thickness and density of the herb layer. The dominance of sexually reproducing taxa and low overall abundance indicate that the studied elevational gradient is characterized by poor resource conditions for soil microarthropods. Oribatid mite species richness and density declined with elevation suggesting that decreasing temperature in concert with resource limitation is a main driver of oribatid mite communities whereas stochastic factors (such as mid-domain effects) are of minor importance.