Andrei S. Zaitsev

RELATIONSHIP AMONG THE SPECIES RICHNESS OF DIFFERENT TAXA

Spatially explicit forecasting of changes in species richness is key to designing informative scenarios on the development of diversity on our planet. It might be possible to predict changes in the richness of inadequately investigated groups from that of groups for which enough information is available. Here we evaluate the reliability of this approach by reviewing 237 richness correlations extracted from the recent literature. Of the 43 taxa covered, beetles, vascular plants, butterflies, birds, ants, and mammals (in that order) were the most common ones examined. Forests and grasslands strongly dominated the ecosystem types studied. The variance explanation (R2) could be calculated for 152 cases, but only 53 of these were significant. An average correlation effect size of 0.374 (95% CI = +/- 0.0678) indicates positive but weak correlations between taxa within the very heterogeneous data set; None of the examined explanatory variables (spatial scale, taxonomic distance, trophic position, biome) could account for this heterogeneity. However, studies focusing on 10-km2 grid cells had the highest variance explanation. Moreover, within-phylum between-class comparisons had marginally significantly lower correlations than between-phylum comparisons. And finally, the explanatory power of studies conducted in the tropics was significantly higher than that of studies conducted in temperate regions. It is concluded that the potential of a correlative approach to species richness is strongly diminished by the overall low level of variance explanation. So far, no taxon has proved to be a universal or even particularly good predictor for the richness of other taxa. Some suggestions for future research are inclusion of several taxa in models aiming at regional richness predictions, improvement of knowledge on species correlations in human dominated systems, and a better understanding of mechanisms underlying richness correlations.

Successional changes of Collembola and soil microbiota during forest rotation

Dynamic approaches to forest ecosystems are surprisingly rare. Here we report about successional changes in collembolan community structure and microbial performances during forest rotation. The study was carried out in a chronosequence of four spruce forest stands (5-, 25-, 45-, and 95 years old; Tharandter forest, Germany). CO2 release significantly increased after clear-cutting and the amount of C stored in the organic layer subsequently declined. The early phase of forest rotation was characterized by a very active decomposer microflora, stimulation of both fungi and bacteria as well as by a high abundance of surface-oriented Collembola. In addition, collembolan species turnover was accelerated. While the biomass of fungi further increased at intermediate stages of forest rotation, the metabolic activity of the microflora was low, the functional diversity of bacteria declined and the collembolan community became impoverished. Euedaphic species dominated during this stage of forest development. These changes can be explained by both reduction in microhabitat diversity and depletion of food sources associated with an accumulation of recalcitrant soil organic matter. Results of the General Regression Model procedure indicate a shift from specific associations between collembolan functional groups and microbiota at the early stage of forest rotation to a more diffuse pattern at intermediate stages. Though the hypothesis that Collembola are relatively responsive to changes in environmental conditions is confirmed, consistently high community similarity suggests a remarkable persistence of some components of microarthropod assemblages. Our study provides evidence for substantial ecosystem-level implications of changes in the soil food web during forest rotation. Moreover, correlations between bacterial parameters and Collembola point to the overarching impact of differences in the composition of the microbial community on microarthropods.

Metal concentrations in soil and invertebrates in the vicinity of a metallurgical factory near Tula (Russia).

Summary To investigate the effects of emissions from a large metal works near Tula in the Russian Federation, we measured concentrations of iron, manganese, zinc, copper, nickel, lead and cadmium in soil, litter and invertebrates at four sampling sites at different distances from the factory. The sites were located in woodlands in the bed of the Voronka river, near the town of Kosaya Gora in the district of Tula. Additional soil properties (organic matter content, clay content, water holding capacity, Ca, Mg, N, P, and pH) were measured that could explain differences in the bioavailability of the metal burdens. It appeared that the factory is a source of Fe, Mn, Zn, Cu, Ni and Pb. One of the sampling sites had a high nitrogen content in the litter due to emissions from a fertilizer plant in the area. Most of the metal contamination was limited to the immediate surroundings and did not extend beyond a distance of 5 km. Only the site close to the factory can be considered as polluted, however, background concentrations of metals in the Tula area seem to be significantly lower than in present Western European soils and a reference system still has to be developed. Exchangeable metal concentrations (0.01 M CaCl 2 extracts from soil) were very low and were not correlated with the total concentrations, indicating low bioavailability of the pollution. At the most polluted site, concentrations of all metals were positively correlated with each other; correlations decreased with increasing distance. Metal concentrations in soil were often negatively correlated with organic matter content, especially so for nickel. Metal concentrations in invertebrates showed considerable variation between individual species, however, some general patterns were obvious. Concentrations were high in earthworms, oribatid mites and carabid beetles, and low in springtails, centipedes and spiders. There was no relationship between the trophic position of a species and its metal accumulating ability. Iron concentrations in invertebrates at the polluted site were a factor of 2 to 4 higher than at the most remote (reference) site; for zinc and copper the internal concentrations were also elevated, but to a lesser extent than the soil concentrations. The data illustrate the extremely complicated relationship between metal residues in invertebrates and metal concentrations in soil. For most of the saprophageous and predatory arthropods studied total concentrations nor exchangeable concentrations in soil are good predictors; species-specific feeding mechanisms and metal physiologies seem to be the main determinants.

Oribatid mite diversity and community dynamics in a spruce chronosequence

Abstract A comparative study on oribatid mite communities was carried out at four sites forming a chronosequence of spruce forest stands (stand age: 5, 25, 45 and 95-years; Tharandter Wald, Germany). A total of 70 species was found. The moderate decline of oribatid species richness at the 5-years-old stand together with a strong deviation from the log-series model indicate that the community had not recovered from initial disturbance after 5 years. Close community similarity between the 5 and the 95-years-old stands nevertheless suggests a delayed response of the oribatid fauna to strong changes in environmental conditions. Species richness significantly increased from 5 to 25-years-old stand. This was accompanied by a strong increase of oribatid abundance that was largely due to the increase of only two species: Oppiella nova and Tectocepheus velatus . Particularly strong deviation from the log-series model at this site suggests that community disturbance becomes most intense at intermediate stages of forest development. Further analyses revealed an alteration of the feeding structure as well as a stimulation of species that either prefer or are at least able to colonize deeper layers of the soil profile in the 25-years-old stand. This indicates marked changes in both nutritional conditions and microclimate in the uppermost horizons 25 years after clear-cutting. A very high C mineralization rate measured in the 5-years-old stand confirms the important contribution of decomposition processes to net ecosystem production in young stands. However, no strong correlation between oribatid mite community variance and environmental conditions could be established by means of a canonical correspondence analysis. It is concluded that oribatid mite communities are a fairly conservative element of the decomposer fauna in temperate spruce forests and might thus be an important component in the decomposer systems buffering mechanisms against strong environmental change. Our data indicate a multifaceted reaction of the oribatid community to long lasting changes in site conditions rather than a straightforward response to certain environmental factors.

Landscape geological age explains large scale spatial trends in oribatid mite diversity

To understand the overwhelming species richness in soil the focus of attention has traditionally been on local soil conditions, such as physical and chemical characteristics. Regional factors like landscape history have been largely ignored. The aim of our study was to assess the importance of geological site age and local site conditions on oribatid mite species richness in undisturbed forest soils. We wanted to evaluate the processes underlying spatial changes in oribatid species richness at the regional level. We selected 41 sites across the Netherlands with different forest types, located on soils with varying levels of humidity and nutrient richness. The selected sites formed a clear spatiotemporal gradient in geological site age, ranging from Holocene sites along the west coast and rivers towards Pleistocene sites in the east of the country. Five samples were collected at each site. Oribatid mites were counted and identified to the species level. In total 145 oribatid mite species were recorded. We observed that oribatid mite species richness across sites was positively affected by site age. Soil nutrient status, water availability, soil type, or forest vegetation type had rather a local modulating effect on soil mite diversity. The increase in species diversity with geological site age was mainly due to an increase in sexually-reproducing species, with an apparent high competitive ability, but lower reproduction rate. Our results suggest that spatial patterns of soil animal community diversity and composition can be significantly determined by geologic age at the regional level.

Shifts in Soil Testate Amoeba Communities Associated with Forest Diversification

We studied changes of testate amoeba communities associated with the conversion of spruce monocultures into mixed beech-fir-spruce forests in the Southern Black Forest Mountains (Germany). In this region, forest conversion is characterized by a gradual development of beech undergrowth within thinned spruce tree stands leading to multiple age continuous cover forests with a diversified litter layer. Strong shifts in the abundance of testate amoeba observed in intermediate stages levelled off to monoculture conditions again after the final stage of the conversion process had been reached. The average number of species per conversion stage (i.e., local richness) did not respond strongly to forest conversion, but the total number of species (i.e., regional richness) was considerably higher in the initial stage than in the mixed forests, due to the large number of hygrophilous species inhabiting spruce monocultures. Functional diversity of the testate amoeba community, however, significantly increased during the conversion process. This shift was closely associated with improved C and N availability as well as higher niche diversity in the continuous cover stands. Lower soil acidity in these forests coincided with a higher relative abundance of eurytopic species. Our results suggest that testate amoeba communities are much more affected by physicochemical properties of the soil than directly by litter diversity.