Micro-arthropod communities under human disturbance: is taxonomic aggregation a valuable tool for detecting multivariate change? Evidence from Mediterranean soil oribatid coenoses

The effects of pollution by multiple metals derived from long-term smelting activities on soil mite communities in arable soils under different land use types in East China

Soil pollution represents a threat to soil biodiversity and to soil and human health. However, many ecotoxicological issues, such as the impact of heavy metal pollution on the soil mite community and its spatial distribution in areas with complex environmental factors, are not fully understood. Here, an investigation was conducted in an arable area (about 11 km²) enclosed by surrounding mountains. The study area was contaminated with potentially toxic metals derived from copper smelting that was functioning for over 10 years. The area comprised four land use types: woodlands, dry fields, paddy fields, and wastelands, and was divided into 141 study sites each with an area of 6.25 ha. The soil metal (Cu, Zn, Pb, and Cd) contents, pH, and organic matter were determined and their distributions were established. Furthermore, soil mite (Acari) community properties (species richness, individual abundance, and Shannon-Wiener diversity index) were determined, and the distributions of total species number and abundance were ascertained. Soil metal pollution strongly reduced soil mite community, but the effects depended on mite groups or species and their sensitivity to different metals as well as land use types. CANOCO analysis revealed that the order Oribatida was more highly correlated with soil metal contents, whereas the other three orders responded to soil metal contents depending on land use types, mite properties, or metals. SADIE method indicated that the coordinate relationship between mite species number and metal concentration was more negative (4-25% of the study sites) than positive (4-12%). The metal pollution levels in the soil were evaluated by single and integrated pollution and ecological risk indices.

Soil mite communities (Acari: Mesostigmata, Oribatida) as bioindicators for environmental conditions from polluted soils

An anthropic ecosystem from Romania was investigated from acarological, vegetation and chemical point of view. The community structures of two groups of mites were studied (Acari: Mesostigmata, Oribatida) from a tailing pond, using transect method, in correlation with concentrations of heavy metals (As, Cu, Pb, Ni, Mn and Zn), with abiotic factors (altitude, aspect, soil temperature, soil humidity, soil pH) and biotic factor (vegetation coverage). Taking into account the mite communities, in total, 30 mite species were identified, with 1009 individuals and 18 immatures (10 species with 59 individuals, 5 immatures of Mesostigmata and 20 species with 950 individuals, 13 immatures of Oribatida). The investigated habitats from the tailing pond were grouped in five transects, with different degree of pollution, based on total metal loads. Taking into account of the connection between mites communities, abiotic factors and heavy metals, each transect were characterized through specific relationship. Using multivariate statistical analysis, we revealed that the occurrence of some Oribatida species was strongly correlated with vegetation coverage, soil pH and soil humidity, though concentrations of Cu, As, Mn, Ni and Zn also had an influence. Pb and Zn concentrations were shown to influence the occurrence of Mesostigmata mites. The heterogeneity of mites species richness at 2 m² scale was correlated with a metric related to the heterogeneity of heavy metals at the same scale.

Responses of soil mite communities (Acari: Oribatida, Mesostigmata) to elemental composition of mosses and pine needles and long-term air pollution in Scots pine (Pinus sylvestris L.) stands

Air pollution is an important threat to biodiversity via deposition of high amounts of heavy metals or nutrients (macroelements). In forest ecosystems contamination can be found in plant tissues and the soil environment including soil mesofauna. However, there is little information on how it influences soil mesofauna. Hence, the aim of the study was to evaluate the reaction of soil mites (Acari: Oribatida, Mesostigmata) to long-term air pollution in mature pine (Pinus sylvestris L.) forests in southwestern Poland. The study was conducted in late autumn between October 2008 and 2010 in eight 5000 m² plots, each within a Scots pine stand. Concentrations of macroelements (C, N, S, Ca, Mg) and heavy metals (Cu, Cr, Cd, Ni, Pb, Zn) were measured in 40 samples of pine needles and 36 bryophyte samples. In total, 360 soil samples were collected for the soil mesofauna analysis. Results of the study include correlations between the sample plot, the year and the soil mite abundance. Among the macroelements analyzed, calcium affected the abundance of mite species the most. Soil mite communities from different forests were dominated by the same species, despite the fact that we found in total 150 mite species, among which there were 106 species of oribatid mites and 44 species of mesostigmatid mites. It seems that, among the elements analyzed, calcium plays the most important, positive role for mite communities. Magnesium had a positive effect on abundance of both mite groups, while nitrogen had a negative effect on diversity of oribatid and mesostigmatid mite communities. Our study indicated that oribatid and mesostigmatid mite communities are stable in areas of long-term contamination, as we did not observe distinct changes in structure and diversity of soil mite assemblages along the pollution gradient.

Linking size spectrum, energy flux and trophic multifunctionality in soil food webs of tropical land-use systems

Many ecosystem functions depend on the structure of food webs, which heavily relies on the body size spectrum of the community. Despite that, little is known on how the size spectrum of soil animals responds to agricultural practices in tropical land-use systems and how these responses affect ecosystem functioning. We studied land-use-induced changes in below-ground communities in tropical lowland ecosystems in Sumatra (Jambi province, Indonesia), a hot spot of tropical rainforest conversion into rubber and oil palm plantations. The study included ca. 30,000 measured individuals from 33 high-order taxa of meso- and macrofauna spanning eight orders of magnitude in body mass. Using individual body masses, we calculated the metabolism of trophic guilds and used food web models to calculate energy fluxes and infer ecosystem functions, such as decomposition, herbivory, primary and intraguild predation. Land-use change was associated with reduced abundance and taxonomic diversity of soil invertebrates, but strong increase in total biomass and moderate changes in total energy flux. These changes were due to increased biomass of large-sized decomposers in soil, in particular earthworms, with their share in community metabolism increasing from 11% in rainforest to 59%-76% in jungle rubber, and rubber and oil palm plantations. Decomposition, that is the energy flux to decomposers, stayed unchanged, but herbivory, primary and intraguild predation decreased by an order of magnitude in plantation systems. Intraguild predation was very important, being responsible for 38% of the energy flux in rainforest according to our model. Conversion of rainforest into monoculture plantations is associated by an uneven loss of size classes and trophic levels of soil invertebrates resulting in sequestration of energy in large-sized primary consumers and restricted flux of energy to higher trophic levels. Pronounced differences between rainforest and jungle rubber reflect sensitivity of rainforest soil animal communities to moderate land-use changes. Soil communities in plantation systems sustained high total energy flux despite reduced biodiversity. The high energy flux into large decomposers but low energy fluxes into other trophic guilds suggests that trophic multifunctionality of below-ground communities is compromised in plantation systems.

Taxonomic resolution and functional traits in the analysis of tropical oribatid mite assemblages

We analysed species-level datasets representing Oribatida assemblages along a gradient of old-growth primary tropical forests, secondary forests, and plantation forests in Dong Nai Biosphere Reserve, Vietnam. We identified patterns in abundance, species richness and species assemblages of Oribatida, then applied taxonomic sufficiency approach to the datasets. Using three levels of higher-taxon aggregation, we evaluated whether aggregated datasets are useful in identifying ecological patterns, in comparison to species-level data. Species-level data on Oribatida assemblages clearly separated plantation forests from other forest environments; there was no significant separation between primary and secondary forests. Geographical structuring of species-level assemblages was significant, separating sites from two regions of the reserve. There was a significant concordance between multivariate ordination plots produced for species-level and aggregated (families, suborders/superfamilies) datasets, with Oribatida assemblages of plantation forests consistently separated from two other forest types. Mycobatidae (at family level) and Ceratozetoidea (at suborder/superfamily level) were indicators of plantation forests. The coarsest taxonomic resolution dataset with only four aggregated groups produced no separation of Oribatida assemblages by forest type or region. Moderate level of taxonomic aggregation applied to Oribatida community data did not cause great differences in patterns revealed by multivariate analysis, and therefore could be a valid approach to analysing the structure of tropical Oribatida assemblages. The taxonomic level of suborders and Brachypylina superfamilies appears to be the best compromise for ecological information and ease of identification. Two traits-body size and reproductive mode-were recorded for collected Oribatida species. Community-weighted mean trait value, modified Mason's index of functional divergence, and Rao's index of functional diversity were calculated for each trait in each of the sampled Oribatida assemblages. Sexual reproduction was a dominant reproductive mode in soil Oribatida and did not vary across forest types, indicating similar levels of resource limitation for this trait. For body size, lower functional divergence in plantation forests suggests less scope for niche differentiation and higher competition among different body sizes in this forest type. Use of functional traits can enhance and complement the analysis of Oribatida communities, but more data are needed on feeding- and diet-related traits in tropical Oribatida.

Comparing the natural variation of oribatid mite communities with their changes associated with anthropogenic disturbance

Several organism communities serve as ecological and environmental indicators to detect changes in human-impacted habitats. However, the composition of indicator communities may vary because of natural variation in addition to the changes associated with human disturbances. This meta-analysis compared the natural variation of oribatid mite assemblages, a good indicator model group in soil ecosystems, with their deviations associated with disturbance using diversity and dissimilarity indices and three human disturbance types. Literature data were collected about oribatid mite assemblages from natural and disturbed habitats. Human disturbances consisted of agriculture, heavy metal pollution and forest management. Biodiversity indices (Shannon and Berger-Parker) and dissimilarity indices (Jaccard and Bray-Curtis) were calculated among natural habitats and between disturbed and control habitats at the species and genus level. We considered oribatid mite assemblages as effective community-level indicators when the methods separated the differences of assemblages between disturbed and control habitats from their varieties among natural habitats. In addition, the study analysed the correlation between these indices and environmental variables of the study sites. Oribatid mite assemblages performed high indication strength with Bray-Curtis index for agricultural disturbances since dissimilarity values between disturbed and control habitats were as high as between different natural habitats and higher than among the same types of natural habitats. Genus-level values showed similar results to the species level. This approach may be useful to test the effectiveness of other indicator groups and methods.

Shortcuts in biodiversity research: What determines the performance of higher taxa as surrogates for species?

Biodiversity research is often impeded by the time and resources required to identify species. One possible solution is to use higher taxa to predict species richness and community composition. However, previous studies have shown that the performance of higher taxa as surrogates for species is highly variable, making it difficult to predict whether the method will be reliable for a particular objective. Using 8 independent datasets, I tested whether higher taxa accurately characterize the responses of beetle and ant communities to environmental drivers. For each dataset, ordinations were carried out using species and higher taxa, and the two compared using the Procrustes m² statistic (a scale‐independent variant of Procrustes sum of squares). I then modelled the relationship between five hypothesised explanatory variables and 1) Procrustes m², and 2) the coefficient of determination (R²) for the correlation between richness of species and higher taxa. The species to higher taxon ratio, community structure, beta diversity, completeness of sampling, and taxon (beetles or ants) were all significant predictors of m², together explaining 88% of the variance. The only significant predictor of R² was the species to higher taxon ratio, which explained 45% of the variance. When using higher taxa to predict community composition, better performance is expected when the ratio of species to higher taxa is low, in communities with high evenness and high species turnover, and when there is niche conservation within higher taxa. When using higher taxa to predict species richness, effective surrogacy can be expected when the species to higher taxon ratio is very low. When it is not, surrogacy performance may be strongly influenced by stochastic factors, making predictions of performance difficult.

Biological activity of the metal-rich post-flotation tailings at an abandoned mine tailings pond (four decades after experimental afforestation)

In the spring 2012, post-flotation tailings of the inactive impoundment Lintich (Slovakia) were sampled. In the impoundment sediment and also in its surrounding, we detected concentration of Pb, Zn, Cd, Cu, and Ba exceeding limiting values. We detected low values of the microbial biomass carbon and microbial activity in the impoundment sediment (LiS) and its dam (DAM) along with potential respiration stayed relatively low and therefore also substrate availability index and metabolic quotient (qCO2) were higher in the control sample (REF) than in the LiS and the DAM. The low qCO2 level indicates that microbial community, despite of dangerously high levels of heavy metals in sediment, is still able to sufficiently utilize sources of available organic carbon. Anyway, we could doubt function of the metabolic index as universal indicator of environment conditions, regarding the anthropogenic substrates. We confirmed changes in composition of the mite communities along gradient dam-impoundment. The percentage of eudominant, recendent, and subrecendent species increased at the expense of dominants and subdominants, all together with decreasing diversity and equitability of the community. We identified species Chamobates borealis, Carabodes rugosior, Metabelba propexa, and Pergalumna nervosa with negative respond under the heavy metal stress. Species Adoristes ovatus was indifferent and Dissorhina sp., Hafenrefferia gilvipes, and Oppiella nova prospered under the loaded conditions. Forty years after experimental afforestation, we expect specific community of actively surviving microorganisms and Oribatida species detected in the DAM are usual in the greatly degraded habitats or on sites in the early succession.

Disturbance, neutral theory, and patterns of beta diversity in soil communities

Beta diversity describes how local communities within an area or region differ in species composition/abundance. There have been attempts to use changes in beta diversity as a biotic indicator of disturbance, but lack of theory and methodological caveats have hampered progress. We here propose that the neutral theory of biodiversity plus the definition of beta diversity as the total variance of a community matrix provide a suitable, novel, starting point for ecological applications. Observed levels of beta diversity (BD) can be compared to neutral predictions with three possible outcomes: Observed BD equals neutral prediction or is larger (divergence) or smaller (convergence) than the neutral prediction. Disturbance might lead to either divergence or convergence, depending on type and strength. We here apply these ideas to datasets collected on oribatid mites (a key, very diverse soil taxon) under several regimes of disturbances. When disturbance is expected to increase the heterogeneity of soil spatial properties or the sampling strategy encompassed a range of diverging environmental conditions, we observed diverging assemblages. On the contrary, we observed patterns consistent with neutrality when disturbance could determine homogenization of soil properties in space or the sampling strategy encompassed fairly homogeneous areas. With our method, spatial and temporal changes in beta diversity can be directly and easily monitored to detect significant changes in community dynamics, although the method itself cannot inform on underlying mechanisms. However, human-driven disturbances and the spatial scales at which they operate are usually known. In this case, our approach allows the formulation of testable predictions in terms of expected changes in beta diversity, thereby offering a promising monitoring tool.

Community-level effects in edaphic fauna from an abandoned mining area: integration with chemical and toxicological lines of evidence

As a part of the Ecological Risk Assessment of a deactivated uranium mining area (Cunha Baixa), the aim of this study was to assess the drivers of litter arthropod community (ecological line of evidence) inhabiting soils with different degrees of contamination. Litter arthropods were collected in the mining area using a total of 70 pitfall traps, in the spring and autumn of 2004. Unlike information previously collected in the chemical and ecotoxicological lines of evidence, we found no clear evidence of impacts of soil contamination on the edaphic arthropod assemblage. Multivariate analyses were unable to extract relevant environmental gradients related to contamination, as most of the sites shared the same taxa overall. Given the consistency of the chemical and ecotoxicological lines of evidence, we must conclude that the litter arthropod assemblage underestimated the impacts of contamination in this abandoned mining area. In part, this could be due to the uncertainty caused by confounding factors that affect the litter arthropod community in the area. Nevertheless, despite the overall lack of responsiveness of the epigeic arthropod community data, a few taxa were negatively correlated with metal concentrations (Clubionidae and Staphylinidae), while Pseudoscorpionida were associated with the toxicological profile of the sites. These evidences suggest that community-level approaches with other animal and plant assemblages are necessary to reduce uncertainty relatively to the assessment of risks in higher evaluation tiers in the Cunha Baixa mine area.

Ant exclusion in citrus over an 8-year period reveals a pervasive yet changing effect of ants on a Mediterranean spider assemblage

Ants and spiders are ubiquitous generalist predators that exert top-down control on herbivore populations. Research shows that intraguild interactions between ants and spiders can negatively affect spider populations, but there is a lack of long-term research documenting the strength of such interactions and the potentially different effects of ants on the diverse array of species in a spider assemblage. Similarly, the suitability of family-level surrogates for finding patterns revealed by species-level data (taxonomic sufficiency) has almost never been tested in spider assemblages. We present a long-term study in which we tested the impact of ants on the spider assemblage of a Mediterranean citrus grove by performing sequential 1-year experimental exclusions on tree canopies for 8 years. We found that ants had a widespread influence on the spider assemblage, although the effect was only evident in the last 5 years of the study. During those years, ants negatively affected many spiders, and effects were especially strong for sedentary spiders. Analyses at the family level also detected assemblage differences between treatments, but they concealed the different responses to ant exclusion shown by some related spider species. Our findings show that the effects of experimental manipulations in ecology can vary greatly over time and highlight the need for long-term studies to document species interactions.

Spatial patterns and autocorrelation in the response of microarthropods to soil pollutants: the example of oribatid mites in an abandoned mining and smelting area

Although exogenous factors such as pollutants can act on endogenous drivers (e.g. dispersion) of populations and create spatially autocorrelated distributions, most statistical techniques assume independence of error terms. As there are no studies on metal soil pollutants and microarthropods that explicitly analyse this key issue, we completed a field study of the correlation between Oribatida and metal concentrations in litter, organic matter and soil in an attempt to account for spatial patterns of both metals and mites. The 50-m wide study area had homogenous macroscopic features, steep Pb and Cu gradients and high levels of Zn and Cd. Spatial models failed to detect metal-oribatid relationships because the observed latitudinal and longitudinal gradients in oribatid assemblages were independent of the collinear gradients in the concentration of metals. It is therefore hypothesised that other spatially variable factors (e.g. fungi, reduced macrofauna) affect oribatid assemblages, which may be influenced by metals only indirectly.