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β‐diversity is a primary biodiversity pattern for inferring community assembly. A randomized null model that generates a standardized β‐deviation has been widely used for this purpose. However, the null model has been much debated and its application is limited to abundance data.Here we derive analytical models for β‐diversity to address the debate, clarify the interpretation and extend the application to occurrence data.The analytical analyses show unambiguously that the standardized β‐deviation is a quantification of the effect size of non‐random spatial distribution of species on β‐diversity for a given species abundance distribution. It robustly scales with sampling effort following a power law with exponent of 0.5. This scaling relationship offers a simple method for comparing β‐diversity of communities of different sizes.Assuming log‐series distribution for the metacommunity species abundance distribution, our model allows for calculation of the standardized β‐deviation using occurrence data plus a datum on the total abundance.Our theoretical model justifies and generalizes the use of the β null model for inferring community assembly rules. [ABSTRACT FROM AUTHOR]

Explaining the mechanisms underlying spatial and temporal variation in community composition is a major challenge. Nevertheless, the processes controlling temporal variation at a site (i.e. temporal β‐diversity, including its turnover and nestedness components) are less understood than those affecting variation among sites (i.e. spatial β‐diversity). Short‐term temporal turnover (e.g. throughout an annual cycle) is expected to correlate positively with seasonal environmental variability and landscape connectivity, but also species pool size (γ‐diversity). We use the megadiverse Amazonian freshwater ichthyofauna as a model to ask whether seasonality and landscape connectivity drive variation in temporal species turnover among geomorphological habitat types, while accounting for between‐habitat variation in γ‐diversity. We collected 11 397 fish representing 260 species during a year‐long sampling program from an area containing the lowland Amazon's four major geomorphological habitat types: rivers, floodplains, terra firme streams, and shield streams. River‐floodplain systems exhibit strong but predictable seasonality (via a high‐amplitude annual flood pulse), high connectivity, and high species richness with many rare species. Terra firme and shield streams exhibit low seasonality, low connectivity, and low species richness with proportionally fewer rare species. Based on these parameters we predicted that river‐floodplain systems should have higher temporal turnover than stream systems. Using a null model approach combined with β‐deviation calculations, we confirmed that rivers and floodplains do exhibit higher turnover (but not nestedness) than terra firme and shield streams, even when controlling for the potentially confounding effect of higher species richness in river‐floodplain systems. All habitats exhibit low temporal nestedness, indicating that short‐term changes in community composition result primarily from temporal species turnover. Our results provide a timely reminder that efforts to conserve the Amazon's threatened aquatic biodiversity should account for the distinct temporal dynamics of habitat types and variation in hydrological seasonality. [ABSTRACT FROM AUTHOR]

Abstract Understanding how species are non‐randomly distributed in space and how the resulting spatial structure responds to ecological, biogeographic, and anthropogenic drivers is a critical piece of the biodiversity puzzle. However, most metrics that quantify the spatial structure of diversity (i.e., community differentiation), such as Whittaker’s β‐diversity, depend on sampling effort and are influenced by species pool size, species abundance distributions, and numbers of individuals. Null models are useful for identifying the degree of differentiation among communities due to spatial structuring relative to that expected from sampling effects, but do not accommodate the influence of sample completeness (i.e., the proportion of the species pool in a given sample). Here, we develop an approach that makes use of individual‐ and coverage‐based rarefaction and extrapolation, to derive a metric, βC, which captures changes in intraspecific aggregation independently of changes in the species pool size. We illustrate the metric using spatially explicit simulations and two case studies: (1) a re‐analysis of the “Gentry” plot data set consisting of small forest plots spanning a latitudinal gradient from North to South America and (2) comparing a large plot in high diversity tropical forests of Barro Colorado Island, Panama, with a plot in a lower diversity temperate forest in Harvard Forest, Massachusetts, USA. We find no evidence for systematic changes in spatial structure with latitude in these data sets. As it is rooted in biodiversity sampling theory and explicitly controls for sample completeness, our approach represents an important advance over existing null models for spatial aggregation. Potential applications range from better descriptors of biogeographic diversity patterns to the consolidation of local and regional diversity trends in the current biodiversity crisis.

Community ecology has so far struggled to integrate both deterministic and stochastic processes into a global model of community variation. To address this issue, we aimed to characterise the ecological conditions that determine the relative importance of deterministic and stochastic community variation in benthic macroinvertebrates. We sampled macroinvertebrate and algal periphyton communities, and microhabitat conditions at monthly intervals over a five year period in two sampling sites in the regulated Durance River and one site in the Asse River (a natural tributary of the Durance). The relative importance of stochastic and deterministic processes was estimated over time as functional and taxonomic spatial β‐deviation (i.e. β‐diversityobs − mean β‐diversitynull/SD β‐diversitynull) for each sampling date and site. We additionally quantified deterministic variation as the trait–environment relationship and predicted a positive correlation with β‐deviation metrics. We found evidence of overdispersal in both functional and taxonomic β‐diversities compared to null expectations. Spatial β‐deviation was highly variable over temporal scales and was jointly explained by invertebrate community size, disturbance (i.e. flooding), periphyton diversity and to a lesser extent, microhabitat diversity. The key factor that explained β‐deviation was recent river discharge (< 90 days), which had a strong negative effect on community size but was also directly associated with higher β‐deviation, likely related to recolonization processes post‐flood. Lastly, we found that when β‐deviation was high, the hydraulic trait–environment relationship was stronger. This indicates that spatial heterogeneity in hydraulic conditions was the main driver of deterministic variation in invertebrate community structure. This study demonstrates that the importance of stochastic processes can vary greatly over short (~ months) and long (~ years) temporal windows with significant consequences for trait–environment relationships. Our study provides an example of how stochastic community variation can be modelled to better interpret deterministic patterns of community structure in natural communities. [ABSTRACT FROM AUTHOR]

Aim Variation in species composition among sites (β-diversity) generally decreases with increasing latitude, but the underlying mechanisms are ambiguous. Although both local and large-scale processes may drive this pattern, they act all through influencing species abundance distribution ( SAD) and spatial pattern of species. A null model incorporating SAD is often used to calculate expected β-diversity, which accounts for most variation in β-diversity. However, a recent study has shown that the deviation of observed β-diversity from expected values (β-deviation) increases with latitude. The latitudinal gradients in β-deviation may be related to both latitudinal differences in SADs and the degrees of spatial aggregation. Our study aims to (1) investigate how β-deviation varies with SAD and spatial aggregation, and (2) separate the contributions of SAD and aggregation in explaining latitudinal gradients in β-deviation. Location Global. Methods 197 forest plots (each containing 10 subplots) distributed along latitudinal gradients were used. Two β-diversity models were derived for communities with randomly and nonrandomly distributed species. The two models were used to simulate relationships of β-deviation with SAD and aggregation, and to separate the contributions of these two factors in explaining latitudinal gradients in β-deviation. Results β-deviation increased with the degree of aggregation and peaked at intermediate species abundance. The fraction of β-deviation linked to SAD increased with latitude in global and regional analyses, whereas the fraction of β-deviation linked to aggregation was only significantly correlated with latitude in New World south. The degree of aggregation increased with latitude in New World south, but not in global extent and New World north. Main conclusions The latitudinal gradients in β-deviation are primarily explained by latitudinal differences in SADs. Additionally, the expected β-diversity is determined solely by SAD. Therefore, we conclude that latitude-β-diversity gradients at local spatial scales appear to be explained by latitudinal differences in SADs. [ABSTRACT FROM AUTHOR]

The relationship between β-diversity and latitude still remains to be a core question in ecology because of the lack of consensus between studies. One hypothesis for the lack of consensus between studies is that spatial scale changes the relationship between latitude and β-diversity. Here, we test this hypothesis using tree data from 15 large-scale forest plots (greater than or equal to 15 ha, diameter at breast height ≥ 1 cm) across a latitudinal gradient (3–30o) in the Asia-Pacific region. We found that the observed β-diversity decreased with increasing latitude when sampling local tree communities at small spatial scale (grain size ≤0.1 ha), but the observed β-diversity did not change with latitude when sampling at large spatial scales (greater than or equal to 0.25 ha). Differences in latitudinal β-diversity gradients across spatial scales were caused by pooled species richness (γ-diversity), which influenced observed β-diversity values at small spatial scales, but not at large spatial scales. Therefore, spatial scale changes the relationship between β-diversity, γ-diversity and latitude, and improving sample representativeness avoids the γ-dependence of β-diversity.

Aim: The mechanisms underlying the maintenance of biodiversity remain to be elucidated. Taxonomic diversity alone remains an unresolved issue, especially in terms of the mechanisms of species co‐existence. We hypothesized that phylogenetic information could help to elucidate the mechanism of community assembly and the services and functions of ecosystems. The aim of this study was to explore the mechanisms driving floral diversity in subtropical forests and evaluate the relative effects of these mechanisms on diversity variation, by combining taxonomic and phylogenetic information. Location: We examined 35 1‐ha tree stem‐mapped plots across eight national nature reserves in Guangxi Zhuang Autonomous Region, China. Taxon: Trees. Methods: We quantified the taxonomic and phylogenetic β‐diversity between each pair of plots using the (abundance‐based) Rao's quadratic entropy and the (incidence‐based) Sørensen dissimilarity indices. Using a null model approach, we compared the observed β‐diversity with the expected diversity at random and calculated the standard effect size of the observed β‐diversity deviation. Furthermore, we used distance‐based redundancy analysis (dbRDA) to partition the variations in taxonomic and phylogenetic observed β‐diversity and β‐deviation into four parts to assess the environmental and spatial effects. Results: The taxonomic β‐deviation was related to and higher than the phylogenetic β‐deviation (r =.74). This indicated that the species turnover between pairwise plots was mainly the turnover of closely related species. Higher taxonomic and phylogenetic β‐deviation were mainly concentrated in the pairwise karst and nonkarst forest plots, indicating that the species in karst forests and nonkarst forests were predominantly from distantly related clades. A large proportions of the variation in taxonomic and phylogenetic β‐deviation were explained by the joint effect of environmental and spatial variables, while the contribution of environmental variables was greater than that of spatial variables, probably owing to the influence of the sampling scale dependence, integrality of sampling size and species pool, and the unique climatic and geomorphic characteristics. Main conclusions: Our study highlights the importance of phylogeny in biodiversity research. The incorporation of taxonomic and phylogenetic information provides a perspective to explore potential underlying mechanisms that have shaped species assemblages and phylogenetic patterns in biodiversity hotspots. [ABSTRACT FROM AUTHOR]

Biodiversity patterns are shaped by the combination of dispersal, environment, and stochasticity, but how the influence of these drivers changes in fragmented habitats remains poorly understood. We examined patterns and relationships among total (γ) and site‐level (α) diversity, and site‐to‐site variation in composition (β‐diversity) of tree communities in structurally contiguous and fragmented tropical rainforests within a human‐modified landscape in India's Western Ghats. First, for the entire landscape, we assessed the extent to which habitat type (fragment or contiguous forest), space and environment explained variation in α‐diversity and composition. Next, within fragments and contiguous forest, we assessed the relative contribution of spatial proximity, environmental similarity, and their joint effects in explaining β‐diversity. We repeated these assessments with β‐diversity values corrected for the confounding effects of α‐ and γ‐diversity using null models (β‐deviation). Lower γ‐diversity of fragments resulted from both lower α‐ and β‐diversity compared to contiguous forests. However, β‐deviation did not differ between contiguous forests and fragments. Fragmented and contiguous forest clearly diverged in floristic composition, which was attributable to β‐diversity being driven by differences in elevation and MAP. Within fragmented forest, neither space nor environment explained β‐diversity, but β‐deviation increased with greater elevational differences. In contiguous forests by comparison, environment alone (mainly elevation) explained the most variation in β‐diversity and β‐deviation of both species' occurrences and abundances. Spatial gradients in environmental conditions played a larger role than dispersal limitation in shaping diversity and composition of tree communities across forest fragments. Thus, location of remnant patches at different elevations was a key factor underlying site‐to‐site variability in species abundances across fragments. Understanding the environmental characteristics of remnant forests in human‐modified landscapes, combined with knowledge of species–environment relationships across different functional groups, would therefore be important considerations for management and restoration planning in human‐modified landscapes. [ABSTRACT FROM AUTHOR]

Increased atmospheric nitrogen (N) deposition affects biodiversity in terrestrial ecosystems. However, we do not know whether the effects of N on above‐ground plant β‐diversity are coupled with changes occurring in the soil seed bank. We conducted a long‐term N‐addition experiment in a typical steppe and found that above‐ground β‐diversity increased and then decreased with increasing N addition, whereas below‐ground β‐diversity decreased linearly. This suggests decoupled dynamics of plant communities and their soil seed bank under N enrichment. Species substitution determined above‐ and below‐ground β‐diversity change via an increasing role of deterministic processes with N addition. These effects were mostly driven by differential responses of the above‐ground vegetation and the soil seed bank β‐diversities to N‐induced changes in environmental heterogeneity, increased soil inorganic N concentrations and soil acidification. Our findings highlight the importance of considering above‐ and below‐ground processes simultaneously for effectively conserving grassland ecosystems under N enrichment. [ABSTRACT FROM AUTHOR]

Aim: Our understanding of the mechanisms driving β‐diversity is still rather rudimentary. This study evaluates the influences of environmental filtering versus spatial scale of regional communities on β‐diversity across latitudes. Location: North‐eastern China. Methods: The β‐diversity was calculated in each regional community. The spatial extent of these "regional communities", which included five or 10 plots, was ≤ 140 km. A random assembly null model was used to assess the effects of species abundance distribution on the β‐diversity. Moreover, the deviation of observed β‐diversity from a null model (called β‐deviation) was also assessed. The variations of the β values were partitioned into environmental, latitudinal and their joint effects. Results: The observed β‐diversity declined with increasing latitude, although the β‐deviations showed a non‐monotonic pattern as the latitude increased at two studied scales. All the regional communities consisting of five or 10 local plots exhibited significantly positive β‐deviations. The total amount of variation in β‐deviations explained by environmental and latitudinal variables increased dramatically with increasing scale. A significant pure environmental effect was observed at both scales, explaining 30% of the variation in β‐deviation for regional communities consisting of five local plots and 58.7% for regional communities consisting of 10 local plots. The spatial variation in precipitation primarily accounted for the β‐gradient. Main conclusions: This is one of the few multiscale analyses to investigate latitudinal patterns and driving mechanisms of tree β‐diversity in temperate forests. The β‐deviation showed a similar trend of change with latitude, but the variation of β‐deviation explained by the environments and latitude was highly dependent on the scale of regional communities studied. Environmental filtering and the spatial scale of regional communities jointly accounted for the β‐gradient, with environmental filtering appearing to determine the high variation of species turnover along the latitudinal gradient. [ABSTRACT FROM AUTHOR]

Soil biodiversity plays a critical role in supporting multiple ecosystem functions. As some of the most diverse and abundant metazoans on the Earth, soil nematode communities exhibit changes along environmental gradients, but the ways in which the abundance and diversity of nematode communities vary along elevational gradients remain poorly understood. Taking advantage of an investigation on Huangshan Mountain, Southeast China, with elevation ranging from 500 to 1200 m, we assessed the abundance and diversity of soil nematodes, as well as the soil physicochemical properties, across subtropical forest ecosystems. Nematode communities were analyzed at the genus level, and the α-diversity was calculated as the genus richness, while the β-diversity was based on the Bray–Curtis dissimilarity. The results showed that, among the top 20 nematode genera ranked by absolute abundance, most genera, such as Eucephalobus, Prismatolaimus, Filenchus, and Rotylenchulus, reached their peak abundance at the highest elevation (1000 m). Additionally, the abundances of Oriverutus, Tylenchus, Criconema, and Tripyla exhibited a positive correlation with the elevation. Moreover, the abundance and α-diversity of the total nematodes and each trophic group of nematodes increased linearly with the elevation, likely due to increased soil moisture at higher elevation. In contrast, the β-diversity of the total nematodes, bacterivores, and herbivores decreased with increasing elevation, indicating the importance of stochastic processes in shaping community assembly at high altitudes. This pattern suggests that as the elevation increases, the nematode communities become more homogeneous in structure. Taken together, our study's findings demonstrate the divergent responses of nematodes' α- and β-diversity to an elevation gradient, highlighting the importance of the soil nematode diversity in maintaining ecosystem functions such as nutrient cycling and food web stability in mountainous regions. These results emphasize the need to incorporate the below-ground biodiversity into conservation strategies, particularly in the face of environmental changes driven by climate and human activities. [ABSTRACT FROM AUTHOR]

Aim Ecologists have generally agreed that β-diversity is driven at least in part by ecological processes and mechanisms of community assembly and is a key determinant of global patterns of species richness. This idea has been challenged by a recent study based on an individual-based null model approach, which aims to account for the species pool. The goal of the present study is twofold: (1) to analyse data sets from different parts of the world to determine whether there are significant latitude-β-diversity gradients after accounting for the species pool, and (2) to evaluate the validity of the null model. Location Global. Methods A total of 257 forest plots, each being 0.1 ha in size and having 10 0.01-ha subplots, were used. We conducted four sets of analyses. A modified version of Whittaker's β-diversity index was used to quantify β-diversity for each forest plot. A randomization procedure was used to determine expected β-diversity. Results The number of individuals per species, which characterizes species abundance distribution, alone explains 56.8-84.2% of the variation in observed β-diversity. Species pool (γ-diversity) explained only an additional 2.6-15.2% of the variation in observed β-diversity. Latitude explains 18.6% of the variation in raw β deviation in Gentry's global data set, and explains 11.0-11.6% of the variation in standardized β deviation in the global and three regional analyses. Latitude explains 33.2-46.2% of the variation in the number of individuals per species. Main conclusions Species abundance distribution, rather than species pool size, plays a key role in driving latitude-β-diversity gradients for β-diversity in local forest communities. The individual-based null model is not a valid null model for investigating β-diversity gradients driven by mechanisms of local community assembly because the null model incorporates species abundance distributions, which are driven by mechanisms of local community assembly and in turn generate β-diversity gradients. [ABSTRACT FROM AUTHOR]

Background: Species turnover (β-diversity) along elevational gradients is one of the most important concepts in plant ecology. However, there is a lack of consensus about the main driving mechanisms of tree β-diversity at local scales in very diverse ecosystems (e.g., Andean mountains), as well as how the sampling effect can alter β-diversity estimations. Recently, it has been hypothesized that patterns of change in β-diversity at local scales along elevational gradients are driven by sampling effects stemming from differences in the size of the species pool rather than by underlying community assembly mechanisms. Thus, we aim to evaluate the relative extent to which sampling effects, such as species pool size, grain size, and tree size cut-off, determine species sorting, and thus, the variability of β-diversity at local scales along elevational gradients in the northwest of Colombia. Results: Using 15 1-ha permanent plots spread out along a 3000 m elevational gradient, we used standardized β-deviation to assess the extent to which either sampling effects or the community assembly mechanisms determine the changes in species composition at local scales. Standardized β-deviation was measured as the difference between the observed and null β-diversity divided by the standard deviation of the null β-diversity. We found that the magnitude of change in local β-deviation along the elevational gradient was significant and dependent on the employed spatial grain size and tree size cut-off. However, β-deviation increased with elevation in all sampling designs, which suggests that underlying community assembly mechanisms play a key role in shaping local β-diversity along the elevational gradient. Conclusions: Our findings suggest that grain size enlargement and the inclusion of trees with small diameters will improve our ability to quantify the extent to which the community assembly mechanisms shape patterns of β-diversity along elevational gradients. Overall, we emphasize the scale-dependent nature of the assessment of β-diversity. Likewise, we call for the need of a new generation of enlarged forest inventory plots along gradients of elevation in tropical forests that include small individuals to improve our understanding about the likely response of diversity and function to global change. [ABSTRACT FROM AUTHOR]

Both regional species pool and local community assembly mechanism drive the microbial diversity patterns across geographical gradients. However, little has been done to separate their effects on the β diversity patterns of microbial communities involved in nitrogen (N) cycling in river ecosystems. Here, we use high‐throughput sequencing of the archaeal amoA, bacterial amoA, nirK, and nirS genes, null model, and neutral community model to distinguish the relative importance of species pool and local assembly processes for ammonia‐oxidizing and denitrifying communities in river wetlands along a latitudinal gradient in eastern China. Results indicated that the β diversity of the nirS‐type denitrifying community co‐varied with γ diversity and environmental heterogeneity, implying that regional species pool and heterogeneous selection explained variation in β diversity. However, the β diversity of ammonia‐oxidizing and nirK‐type denitrifying communities did not correlate with γ diversity and environmental heterogeneity. The continuous hump distribution of β deviation along the latitudinal gradient and the lower species dispersal rate indicated that the dispersal limitation shaped the variation in β diversity of ammonia‐oxidizing and nirK‐type denitrifying communities. Additionally, biotic interactions drove ammonia‐oxidizing and nirS‐type denitrifying communities by influencing species co‐occurrence patterns. Our study highlights the importance of regional species pool and local community assembly processes in shaping geographical patterns of N‐cycling microorganisms and extends knowledge of their adaptability to a continuously changing environment on a large scale. [ABSTRACT FROM AUTHOR]

The effect of the metallic layer thickness on the stress-strain state and strength of thick-walled metal-composite cylinders of total constant thickness under internal dynamic pressure produced by the explosion of a charge uniformly distributed along its axis in air at the constant total-to-running charge mass ratio ξ = 1.421 mm was numerically investigated. The strength of the cylinders was evaluated by the generalized Mises criterion. It is numerically and analytically proved that the strength of circularly reinforced cylinders from the composites of low tensile strength in the isotropy plane is primarily governed by the wave processes across the shell width and, as a consequence, by radial and axial tensile stresses, viz the larger they are, the lower the strength. Circumferential tensile stresses, on the contrary, improve the strength in most cases, i.e., only strengthen the structural element and increase the safety margin. Cylinders with four outer layer composites are examined. They are double-layered: the inner layer is steel (St20), the outer layer is a circularly reinforced composite. At given ξ and the total constant cylinder thickness H , the optimum in strength terms ratio β opt of the metallic layer thickness h to H is strongly dependent on a composite (i.e., its physicomechanical characteristics) and varies within 0.3–0.7. The plastic deformation of the inner steel layer has a significant impact on the shell strength, the account of the plastic steel deformation substantially changes the dynamics of objects both qualitatively and quantitatively, thus, the strength function can be reduced by more than 50% compared to the elastic calculation. The strength of metal-composite cylinders is proved to be very sensitive to the wave phenomena along the radial coordinate. Sometimes at a certain ratio of layers β (about 0.7), the charge mass ratio ξ (and hence the absolute charge mass M ) can be increased more than twice without deterioration of the strength requirements, while the β deviation by only 1.5% from that at given ξ would lead to the cylinder fracture. [ABSTRACT FROM AUTHOR]

Summary: In this study, we investigated microbial communities (bacteria and protist) in two coastal areas near the estuaries of the Liaohe (LH) River and Yalujiang (YLJ) River in the Northwestern Pacific Ocean. Due to the existence of Liaodong Peninsula and different levels of urbanization, geographical segregation and significant environmental heterogeneity were observed between these two areas. There were significantly different regional species pools and biogeographic patterns for both bacterial and protistan communities between LH and YLJ coastal areas. Species turnover was the main mechanism driving β‐diversity patterns of both bacterial and protistan communities in each area. In addition, the contributed ratio of nestedness to the β‐diversity patterns was significantly higher for protists compared to bacteria. Variation in regional species pools was found to be the dominant driver of differences of bacterial and protistan communities between the LH and YLJ coastal areas. For a single‐studied area, local community assembly mechanisms, including heterogeneous selection and dispersal limitation, were found to shape the bacterial and protistan communities through calculation of the β‐deviation index. Among them, the relative importance of heterogeneous selection and dispersal limitation on the community assembly varied according to microorganism type and habitat. [ABSTRACT FROM AUTHOR]

Aim: The contemporary coexistence theory suggests that species pool, environmental filtering, dispersal assembly processes, ecological drift and biotic interactions collectively determine the β‐diversity of communities. However, we know little about the biogeographical patterns of the β‐diversity of microbial communities harbouring the alkaline phosphatase phoD gene (phoD communities, hereafter) and whether these mechanisms are all‐important in shaping phoD communities' β‐diversity in natural steppe ecosystems. Location: Northern Hemisphere steppes. Time period: July to August 2018. Major taxa studied: Alkaline phosphatase (phoD gene) encoding community. Methods: Using the high throughput amplicon sequencing method, soil phoD communities were comparatively studied along three representative regions of the Northern Hemisphere steppes, namely the Qinghai‐Tibetan Plateau, Inner Mongolian Plateau and the Loess Plateau. Each region harbours three types of steppes (habitats): meadow, typical and desert steppes. Results: We observed significantly higher phoD β‐diversity in the Qinghai‐Tibetan than in the Loess and Inner Mongolian Plateaus and significantly lower β‐diversity in the typical steppes than in other steppe types. The decay rates of phoD β‐diversity with geographical distance varied in different steppe regions and types. The phoD β‐diversity was not significantly influenced by species pool; instead, environmental filtering, dispersal assembly processes, ecological drift and biotic interactions jointly shaped the β‐diversity patterns. The β‐deviation variations (β‐diversity excluding the effects of species pool) were influenced by spatial and environmental factors and biotic interactions, among which soil pH was the key environmental determinant. The soil pH driving β‐diversity mechanism was steppe region and habitat specific. Main conclusions: The biogeographical patterns of phoD β‐diversity were mainly driven by local community assembly processes in the Northern Hemisphere steppes. [ABSTRACT FROM AUTHOR]

Anthropogenic nitrogen (N) input is known to alter plant and microbial α‐diversity, but how N enrichment influences β‐diversity of plant and microbial communities remains poorly understood. Using a long‐term multilevel N addition experiment in a temperate steppe, we show that plant, soil bacterial and fungal communities exhibited different responses in their β‐diversity to N input. Plant β‐diversity decreased linearly as N addition increased, as a result of increased directional environmental filtering, where soil environmental properties largely explained variation in plant β‐diversity. Soil bacterial β‐diversity first increased then decreased with increasing N input, which was best explained by corresponding changes in soil environmental heterogeneity. Soil fungal β‐diversity, however, remained largely unchanged across the N gradient, with plant β‐diversity, soil environmental properties, and heterogeneity together explaining an insignificant fraction of variation in fungal β‐diversity, reflecting the importance of stochastic community assembly. Our study demonstrates the divergent effect of N enrichment on the assembly of plant, soil bacterial and fungal communities, emphasizing the need to examine closely associated fundamental components (i.e., plants and microorganisms) of ecosystems to gain a more complete understanding of ecological consequences of anthropogenic N enrichment. [ABSTRACT FROM AUTHOR]

Ecological drift can override the effects of deterministic niche selection on small populations and drive the assembly of some ecological communities. We tested this hypothesis with a unique data set sampled identically in 200 streams in two regions (tropical Brazil and boreal Finland) that differ in macroinvertebrate community size by fivefold. Null models allowed us to estimate the magnitude to which β‐diversity deviates from the expectation under a random assembly process while taking differences in richness and relative abundance into account, i.e., β‐deviation. We found that both abundance‐ and incidence‐based β‐diversity was negatively related to community size only in Brazil. Also, β‐diversity of small tropical communities was closer to stochastic expectations compared with β‐diversity of large communities. We suggest that ecological drift may drive variation in some small communities by changing the expected outcome of niche selection, increasing the chances of species with low abundance and narrow distribution to occur in some communities. Habitat destruction, overexploitation, pollution, and reductions in connectivity have been reducing the size of biological communities. These environmental pressures might make smaller communities more vulnerable to novel conditions and render community dynamics more unpredictable. Incorporation of community size into ecological models should provide conceptual and applied insights into a better understanding of the processes driving biodiversity. [ABSTRACT FROM AUTHOR]

Grassland degradation caused by increases in livestock grazing threatens a variety of ecosystem services. Understanding changes in plant community assembly during the process of grassland degradation in the presence of grazing is important to help restore degraded grasslands worldwide but has received little attention thus far. The grassland degradation process is typified by heterogeneous degradation, that is, gradual formation of degraded patches (hereafter "patchy degradation"). Here, we experimentally examined the effects of herbivore grazing and patchy degradation on plant community assembly using nine pairs of non‐degraded (intact) and patch‐degraded (fragmented) grasslands subject to grazing by different‐sized herbivores (i.e., NG, no grazing; SG, sheep grazing; CG, cattle grazing) over 4 years. Using a null‐model approach, we estimated the relative magnitude of deterministic processes of community assembly by comparing the observed and expected β‐diversity. We found that in the absence of herbivore grazing, deterministic processes played a greater role in community assembly, regardless of whether patchy degradation had occurred. However, the deterministic processes resulted in plant communities being more spatially similar in non‐degraded grasslands while being more dissimilar in patchy degraded grasslands. Compared with non‐degraded grasslands, species with strong competitive abilities (i.e., Leymus chinensis) were less dominant in patchy degraded grasslands, indicating relaxed competition and a reduced role of species interactions over plant communities. Instead, patchy degradation added the role of environmental variables over plant communities. SG consistently promoted more stochastic plant community assembly in both non‐degraded and patch‐degraded grasslands, while CG promoted more stochastic plant community assembly only in the non‐degraded state, having no effect in the patch‐degraded state. Our study offers important insights into changes in plant community assembly during ongoing patch‐degradation of grasslands, indicating the role of increased environmental filtering of soil and reduced species interactions in driving plant community dynamics with increasing grassland patchy degradation. We also uncovered an herbivore species‐specific effect on plant community assembly during the process of grassland degradation, which will better inform and improve future grassland restoration planning efforts. [ABSTRACT FROM AUTHOR]

Pneumatic impactor is widely used in the drilling process of various medium and high hard rocks with poor drill ability. Currently, there is relatively little analysis on the impact of the inclination of the rock surface during the drilling process on the drilling efficiency and excavation capability of pneumatic impactors. Based on the dynamic theory of impact drilling and finite element method (FEM), the constitutive model of HJC criterion and INVENTOR 3D mechanical structure design software, a 3D numerical analysis system of piston-bit head-rock during pneumatic impactor drilling is established by ANSYS LS-DYNA, a nonlinear dynamic analysis software. The numerical results of drilling force at different incidence angles are analyzed in detail. For the rock without initial hole, the ratio of maximum to minimum drilling force under the conditions of considering incidence angle δ, only considering incidence angle β and considering both β and δ is 3.114, 3.161 and 3.873, respectively. For the rocks with initial holes, the ratio of maximum to minimum drilling force under the same and different incidence angles is 1.810 and 2.090, respectively. Through nonlinear fitting for numerical results, the corresponding fitting solution is obtained, and the relative error between fitting solution and numerical solution is analyzed to be between 11.72%~15.58%, which can meet the requirements of engineering application. The analysis results provide references for the mechanical structural optimization design and use of pneumatic impactor. [ABSTRACT FROM AUTHOR]

The tendency of relative motion via rolling between contacting objects exists in various aspects of industry and nature because, in many practical situations, forces and moments may be simultaneously induced at the contacting interfaces. Due to the presence of adhesion, which may be prominent on small scales, research on contacts with the tendency to roll, termed herein as rolling adhesion, is very limited. In the present work, a novel double-Hertz model is developed for adhesive contact between spherical objects subjected to the combined action of normal forces and moments. The results from the new model agree well with available numerical simulations and experimental results. It has been demonstrated that the contact behavior with the effect of rolling adhesion seemingly resembles that of conventional adhesive contact, but the applied moment may impact the pull-off force and may even induce novel contact instability if large enough. The resistance moment at the interface has also been obtained analytically, which is proportional to adhesion hysteresis and contact area. Given the applicability to the full range of the Tabor parameter and nonsingular stresses involved, these results might shed light on adhesive contacts with rolling adhesion and help to characterize them better than existent models. [ABSTRACT FROM AUTHOR]

Geminiviridae are ssDNA plant viruses whose control has both economical and agricultural importance. Their capsids assemble into two distinct architectural forms: (i) a T = 1 icosahedral and (ii) a unique twinned quasi-isometric capsid. Described here are the high-resolution structures of both forms of the maize streak virus using cryo-EM. A comparison of these two forms provides details of the coat protein (CP) and CP–CP and CP–genome interactions that govern the assembly of the architecture of the capsids. Comparative analysis of other representative members of Geminiviridae reveals structural conservation of 60–95% compared to a sequence similarity of 21–30%. This study provides a structural atlas of these plant pathogens and suggests possible antiviral-targetable regions of these capsids. [ABSTRACT FROM AUTHOR]

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Understanding how and why β‐diversity varies along latitude is a long‐standing challenge in community ecology and rarely addressed in both space and time. We aimed to explore the spatiotemporal variations in macroinvertebrate β‐diversity and their underlying drivers in eight biogeographic regions covering a substantial latitudinal gradient of more than 40 degrees. By combining β‐diversity partitioning and distance decay of community similarity analyses, we found that subtropical β‐diversity varies more in space relative to variation in time compared with temperate β‐diversity, as we predicted. This is probably because subtropical β‐diversity is shaped by species–environment sorting (SS), caused by habitat heterogeneity and species specialization, more strongly in space relative to time than temperate β‐diversity. Our study highlights the importance of SS in shaping latitudinal gradients of β‐diversity in space and time. [ABSTRACT FROM AUTHOR]

The climate and soil properties are major determinants of plant growth and forest community assembly across diverse biomes. However, the contribution of climate and soil on species diversity in tropical and subtropical forests remains controversial. Therefore, this study aims to evaluate the effects of soil and climate on tree species richness using survey data across 495 tropical and subtropical forest plots in Southern China. The selected predictors were categorized as local plot characteristics, climate, and soil factors, and their relationship with tree species richness was modeled using negative binomial generalized linear models. The results revealed that the considering of the interaction between climate and soil properties considerably improved the goodness−of−fit of these models. The individual effects of climate and soil factors had weak relationships with species richness, accounting for 3.61% and 5.77% of the overall 58.9% explained variance in species richness, respectively. Instead, the interaction between climate and soil properties explained most of the statistical variation in tree species richness (84.34% of the overall 58.9% explained variance). The results highlight the importance of soil and climate interactions on tree diversity in tropical and subtropical mature natural forests and their incorporation into biodiversity assessment models to enhance the prediction of community change and responses to climate change. [ABSTRACT FROM AUTHOR]

Abstract Background Species turnover (β-diversity) along elevational gradients is one of the most important concepts in plant ecology. However, there is a lack of consensus about the main driving mechanisms of tree β-diversity at local scales in very diverse ecosystems (e.g., Andean mountains), as well as how the sampling effect can alter β-diversity estimations. Recently, it has been hypothesized that patterns of change in β-diversity at local scales along elevational gradients are driven by sampling effects stemming from differences in the size of the species pool rather than by underlying community assembly mechanisms. Thus, we aim to evaluate the relative extent to which sampling effects, such as species pool size, grain size, and tree size cut-off, determine species sorting, and thus, the variability of β-diversity at local scales along elevational gradients in the northwest of Colombia. Results Using 15 1-ha permanent plots spread out along a 3000 m elevational gradient, we used standardized β-deviation to assess the extent to which either sampling effects or the community assembly mechanisms determine the changes in species composition at local scales. Standardized β-deviation was measured as the difference between the observed and null β-diversity divided by the standard deviation of the null β-diversity. We found that the magnitude of change in local β-deviation along the elevational gradient was significant and dependent on the employed spatial grain size and tree size cut-off. However, β-deviation increased with elevation in all sampling designs, which suggests that underlying community assembly mechanisms play a key role in shaping local β-diversity along the elevational gradient. Conclusions Our findings suggest that grain size enlargement and the inclusion of trees with small diameters will improve our ability to quantify the extent to which the community assembly mechanisms shape patterns of β-diversity along elevational gradients. Overall, we emphasize the scale-dependent nature of the assessment of β-diversity. Likewise, we call for the need of a new generation of enlarged forest inventory plots along gradients of elevation in tropical forests that include small individuals to improve our understanding about the likely response of diversity and function to global change.

Spiroplasma virus 4 (SpV4) is a bacteriophage of the Microviridae, which packages circular ssDNA within non-enveloped T = 1 icosahedral capsids. It infects spiroplasmas, which are known pathogens of honeybees. Here, the structure of the SpV4 virion is determined using cryo-electron microscopy to a resolution of 2.5 Å. A striking feature of the SpV4 capsid is the mushroom-like protrusions at the 3-fold axes, which is common among all members of the subfamily Gokushovirinae. While the function of the protrusion is currently unknown, this feature varies widely in this subfamily and is therefore possibly an adaptation for host recognition. Furthermore, on the interior of the SpV4 capsid, the location of DNA-binding protein VP8 was identified and shown to have low structural conservation to the capsids of other viruses in the family. The structural characterization of SpV4 will aid future studies analyzing the virus–host interaction, to understand disease mechanisms at a molecular level. Furthermore, the structural comparisons in this study, including a low-resolution structure of the chlamydia phage 2, provide an overview of the structural repertoire of the viruses in this family that infect various bacterial hosts, which in turn infect a wide range of animals and plants. [ABSTRACT FROM AUTHOR]

The zoonotic viruses pose significant threats to public health. Nipah virus (NiV) is an emerging virus transmitted from bats to humans. The NiV causes severe encephalitis and acute respiratory distress syndrome, leading to high mortality rates, with fatality rates ranging from 40% to 75%. The first emergence of the disease was found in Malaysia in 1998–1999 and later in Bangladesh, Cambodia, Timor‐Leste, Indonesia, Singapore, Papua New Guinea, Vietnam, Thailand, India, and other South and Southeast Asian nations. Currently, no specific vaccines or antiviral drugs are available. The potential advantages of epitope‐based vaccines include their ability to elicit specific immune responses while minimizing potential side effects. The epitopes have been identified from the conserved region of viral proteins obtained from the UniProt database. The selection of conserved epitopes involves analyzing the genetic sequences of various viral strains. The present study identified two B cell epitopes, seven cytotoxic T lymphocyte (CTL) epitopes, and seven helper T lymphocyte (HTL) epitope interactions from the NiV proteomic inventory. The antigenic and physiological properties of retrieved protein were analyzed using online servers ToxinPred, VaxiJen v2.0, and AllerTOP. The final vaccine candidate has a total combined coverage range of 80.53%. The tertiary structure of the constructed vaccine was optimized, and its stability was confirmed with the help of molecular simulation. Molecular docking was performed to check the binding affinity and binding energy of the constructed vaccine with TLR‐3 and TLR‐5. Codon optimization was performed in the constructed vaccine within the Escherichia coli K12 strain, to eliminate the danger of codon bias. However, these findings must require further validation to assess their effectiveness and safety. The development of vaccines and therapeutic approaches for virus infection is an ongoing area of research, and it may take time before effective interventions are available for clinical use. [ABSTRACT FROM AUTHOR]

Biodiversity patterns across geographical gradients could result from regional species pool and local community assembly mechanisms. However, little has been done to separate the effects of local ecological mechanisms from variation in the regional species pools on bacterial diversity patterns. In this study, we compare assembly mechanisms of soil bacterial communities in 660 plots from 11 regions along a latitudinal gradient in eastern China with highly divergent species pools. Our results show that β diversity does not co-vary with γ diversity, and local community assembly mechanisms appear to explain variation in β diversity patterns after correcting for variation in regional species pools. The variation in environmental conditions along the latitudinal gradient accounts for the variation in β diversity through mediating the strength of heterogeneous selection. In conclusion, our study clearly illustrates the importance of local community assembly processes in shaping geographical patterns of soil bacterial β diversity. The relative importance of regional species pool and local assembly processes as drivers of beta diversity is unclear. Here the authors investigate soil bacterial diversity patterns along a 3700-km latitudinal gradient in Chinese forests, finding that community assembly processes differ based on environmental heterogeneity. [ABSTRACT FROM AUTHOR]

Questions: Changes in vegetation structure, including shrub expansion, occur in forest–tundra ecotones in sub‐arctic regions. However, the community‐level processes driving vegetation change are poorly understood. We aimed to evaluate factors mediating the assembly processes for community initiators of vegetation change and determine the ecological processes driving vegetation changes. Location: Kuujjuarapik/Whapmagoostui (55.31 N, 77.75 W), Quebec, Canada. Methods: Vegetation was surveyed in eight 100‐m line transects with 16 quadrats (1 m × 1 m) per transect established in both forest and tundra habitats. To elucidate the assembly processes of the initiators of vegetation change and other community components of the forest–tundra ecotone, we evaluated β‐diversity among and within habitats and its causal factors (i.e. spatial and environmental factors). Interspecies interactions were estimated based on the patterns of co‐occurrence between all pairs of species. Results: Although environmental and spatial factors significantly affected the community structure of the specific and shared species in the forest habitat, the variation in community structure within and among tundra habitats was not explained by environmental or spatial factors for any community components. Therefore, community assemblages of shared species in tundra habitat were independent from local conditions determined by environment and spatial location. However, we found a positive co‐occurrence pattern among the dominant shared shrubs to be a characteristic of the tundra habitat, and this relationship explained the patterns of community structure within tundra habitats. Conclusions: Community assemblages of initiators of vegetation change in tundra habitats are unrestricted by any external factors, such as dispersal limitation or environmental filtering. However, positive relationships in the abundance or occurrence of dominant shrubs may indicate a positive feedback loop between colonizing species and environmental modifications. This positive feedback loop may be a driving process in the expansion of shared species and vegetation change. [ABSTRACT FROM AUTHOR]

In this study, the results are presented and discussed from laboratory test campaigns specifically designed to investigate the behavior of sacrificial piles as a countermeasure against local scouring at a circular bridge pier and clear-water conditions with flow intensity slightly below the threshold of sediment motion. Sacrificial piles are assessed on the upstream side of the pier in two transverse and triangular arrangements. Piles can reduce scouring by deflecting the flow and creating a low-velocity wake region behind them. The efficiency of the piles against local scouring depends on the diameter of the piles, the number of piles, and the angle of the wedge. The investigation was aimed at evaluating the effectiveness of the sacrificial piles as a function of different dimensionless groups. It was found that the triangular arrangement of sacrificial piles has better results than the transverse arrangement. The results showed that the triangular sacrificial piles reduced the maximum local scour depth at the pier to 37.2% in the best configuration. Combined countermeasures were tested, which were composed of sacrificial piles and a bed sill downstream of the pier; in the best configuration, the scour depth reduction in front of the pier reached 51.1%. The increased efficiency of the combination of bed sill and sacrificial piles (BSSP) is an advantage that can reduce the risk of pier failure when the duration of the flood is short. This last result shows that a combination of BSSP may be a very effective countermeasure against local scouring at bridge piers. Finally, the coherent turbulent flow structure around the best combination of BSSP was investigated, and its effect on the bed scouring pattern was studied. A 3D analysis of the bursting process was used. Turbulence characteristics, as well as the occurrence and transition probabilities of bursting events, were calculated. The obtained results confirmed the quite effective effect of the combination of these two countermeasures in reducing the scour depth. [ABSTRACT FROM AUTHOR]

This study investigates the experimental and analytical torsional behavior of reinforced concrete (RC) bridge box girders reinforced with glass fiber–reinforced polymer (GFRP) bars and continuous spiral stirrups, representing a first in literature. Reinforced concrete box girders were constructed and examined until failure to assess the influence of the spiral pitch and web reinforcement configuration on torsional behavior and strength. The test specimens had continuous GFRP spirals and tie stirrups; the control specimen did not have web reinforcement. The specimens were 4,000 mm long, 380 mm wide, and 380 mm high, and had a wall thickness of 100 mm. The test results demonstrate that the box girder with spiral GFRP reinforcement achieved higher torsional strength and lower twist than its counterpart specimen reinforced with individual GFRP tie stirrups by approximately 6% and 11%, respectively. The specimen with a narrow spiral pitch performed better than the specimens with a wide spiral pitch. An analytical iterative softened membrane model for torsion (SMMT) was used to estimate the entire torsional behavior of box girders with spiral GFRP reinforcement. The analytical results were compared with the experimental results of four bridge box girders with spiral GFRP reinforcement to validate the model's accuracy. The comparison indicates that the model could reasonably predict the cracking and ultimate torsional strength as well as the associated twists. [ABSTRACT FROM AUTHOR]

The way of approaching the flood hazard in the Dobrogea Hydrographic Area consists in a first phase in the grouping of registered water courses on three levels of detail according to the frequency of floods in recent years, their amplitude, the form of manifestation, the degree of equipping with works of defence against floods, social or economic objectives subject to flood hazard. The causes of these floods were the amounts of precipitation from torrential rains recorded in a certain period of time. Due to the flood waves, the danger levels were exceeded, some sectors of the permanently flowing watercourses were flooded. In Nuntași, between 02.09-04.09.1999, the flood produced on the Nuntaşi river destroyed houses, cultures, lives, etc. The assessment of the water resources in this basin consists in the assessment of the hydrographic and hydrogeological basins, which together form the reception basin. surface, shape, hypsometric curve and average altitude of the basin, average slope, vegetation cover, hydrogeological basin, hydrograph, rainfall hyetogram, etc.) The risk analysis of the NUNTAȘI hydrographic space consists in the measurement and quantification of 4 parameters using the RkFMEA method (RisK Failure Mode Evaluation Analysis): vulnerability (exposure) (R), probability (P), the effect of the existence of a control instrument/measure/control/action (N) and the efficiency indicator of a new measure (F). The simple risk level (RPN factor) and the efficiency factor F (complex risk level, RPNF) were automatically calculated. The conclusion of the risk analysis was: the NUNTAȘI bed falls under "low risk with serious prevention measure without any urgent implementation with RPNF values between (1...150)". [ABSTRACT FROM AUTHOR]

Aim: To quantify the relative contributions of local community assembly processes versus γ‐diversity to β‐diversity, and to assess how spatial scale and anthropogenic disturbance (i.e. nutrient enrichment) interact to dictate which driver dominates. Location: France and the United States. Time period: 1993–2011. Major taxa studied: Freshwater stream diatoms. Methods: β‐diversity along a nutrient enrichment gradient was examined across multiple spatial scales. β‐diversity was estimated using multi‐site Sørensen dissimilarity. We assessed the relative importance of specialists versus generalists using Friedley coefficient, and the contribution of local community assembly versus γ‐diversity to β‐diversity across spatial scales, with a null model. Finally, we estimated the response of β‐diversity to environmental and spatial factors by testing the correlations between community, environmental and geographical distance matrices with partial Mantel tests. Results: β‐diversity generally increased with spatial scale but the rate of increase depended on nutrient enrichment level. β‐diversity decreased significantly with increasing nutrient enrichment level due to the loss of specialist species. Local assembly was an important driver of β‐diversity especially under low nutrient enrichment. Significant partial Mantel correlations were observed between diatom β‐diversity and pure environmental distances under these conditions, highlighting the role of species sorting in local assembly processes. Conversely, in heavily enriched sites, only spatial distances were significantly correlated with β‐diversity, which indicated a substantial role of dispersal processes. Main conclusions: Nutrient concentration mediated the expected increase in β‐diversity with spatial scales. Across spatial scales, β‐diversity was more influenced by local assembly processes rather than by γ‐diversity. Nutrient enrichment was associated with an overall decline in diatom β‐diversity and a shift in assembly processes from species sorting to dispersal, notably due to the elimination of some specialists and their subsequent replacement by generalists. [ABSTRACT FROM AUTHOR]