Assembly Rules Research Articles

Can high-resolution topography and forest canopy structure substitute microclimate measurements? Bryophytes say no

Increasingly available high-resolution digital elevation models (DEMs) facilitate the use of fine-scale topographic variables as proxies for microclimatic effects not captured by the coarse-grained macroclimate datasets. Species distributions and community assembly rules are, however directly shaped by microclimate and not by topography. DEM-derived topography, sometimes combined with vegetation structure, is thus widely used as a proxy for microclimatic effects in ecological research and conservation applications. However, the suitability of such a strategy has not been evaluated against in situ measured microclimate and species composition. Because bryophytes are highly sensitive to microclimate, they are ideal model organisms for such evaluation.To provide this much needed evaluation, we simultaneously recorded bryophyte species composition, microclimate, and forest vegetation structure at 218 sampling sites distributed across topographically complex sandstone landscape. Using a LiDAR-based DEM with a 1 m resolution, we calculated eleven topographic variables serving as a topographic proxy for microclimate. To characterize vegetation structure, we used hemispherical photographs and LiDAR canopy height models. Finally, we calculated eleven microclimatic variables from a continuous two-year time- series of air and soil temperature and soil moisture. To evaluate topography and vegetation structure as substitutes for the ecological effect of measured microclimate, we partitioned the variation in bryophyte species composition and richness explained by microclimate, topography, and vegetation structure.In situ measured microclimate was clearly the most important driver of bryophyte assemblages in temperate coniferous forests. The most bryophyte-relevant variables were growing degree days, maximum air temperature, and mean soil moisture. Our results thus showed that topographic variables, even when derived from high-resolution LiDAR data and combined with in situ sampled vegetation structure, cannot fully substitute effects of in situ measured microclimate on forest bryophytes.

The Mechanisms of Collective Resilience in a Crisis Context: The Case of The 'COVID-19' Crisis.

In this research, we claim to join the efforts of practitioners and researchers to provide managerial responses to an unprecedented health crisis such as COVID-19. To do this, we study the concept of 'collective resilience' as a mechanism for responding to crisis in the Tunisian context. The aim of this research is to explain the impact of collective resilience processes on the ability of organizations to withstand crisis. We conducted sixteen semi-structured interviews with Tunisian companies that had experienced the COVID-19 crisis. Continuous analysis of these interviews was carried out with the Nvivo12 software. Our results showed a positive effect of collective resilience on the capacity of organizations to resist the COVID-19 crisis by developing protective factors. These are manifested by new intersubjective interactions (massive exchanges, shared representation, collective consciousness, collaboration, solidarity, mutual aid, etc.), generic interactions (actions and assembly rules not used before: less formalized rules and procedures, more flexible and decentralized structure, new organizational diagrams based on trust, accountability, etc.) and finally the improvisation and tinkering of the organization which made it possible to bring about a change affecting all levels of the organization: strategic and organizational.

Divergent Abiotic Stressors Drive Grassland Community Assembly of Tibet and Mongolia Plateau.

Multiple ecological processes simultaneously govern community assembly, but it remains unclear how abiotic stressors regulate the relative importance of these processes among different biogeographic regions. Therefore, we conducted a comprehensive study on the responses of community assembly to varying environmental gradients, using the mean, variance, skewness, and kurtosis of plant height (height), specific leaf area (SLA) and leaf dry matter content (LDMC) distributions on the Tibetan Plateau (TP) and the Mongolian Plateau (MP). Our results showed that the prevalence of trait convergence across all grasslands in both TP and MP seem to be the result of abiotic filtering or weaker competitive exclusion etc. These trait-convergence assembly processes decrease the functional dispersion but increase the evenness of the trait frequency distribution. The mean, variance, skewness, and kurtosis responses of grassland communities to abiotic stress varied between the TP and MP. On average, plant trait distribution was mainly driven by temperature on the TP, and low-temperature stress altered the community assembly rules. In contrast, water availability shaped plant trait frequency distributions on the MP, and drought stress mediated the balance between different assembly processes. Our results provide empirical evidence that divergent abiotic stressors regulate the grassland community assembly on the TP and MP. Together, our study speculates that different aspects of future climate change, such as climate warming and changing precipitation patterns, on community assembly are dependent on regional climatic regimes.

大数据时代土壤微生物地理学研究综述

PDF HTML阅读 XML下载 导出引用 引用提醒 大数据时代土壤微生物地理学研究综述 DOI: 10.5846/stxb202107061805 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目(91951206,41630857) Advances and perspectives of soil microbial biogeography at big data era Author: Affiliation: Fund Project: National Natural Science Foundation of China 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:土壤蕴含极为丰富的微生物多样性,它们在物质分解、元素生物地球化学循环、植物生产力和生物健康中扮演着关键角色。理解土壤微生物的生物地理分布格局、形成机制与群落构建规则,有助于预测在全球变化背景下土壤微生物组的功能演变及其对陆地生态系统的调控影响。自21世纪以来,土壤微生物生物地理学在各种大型国际微生物计划的推动下逐步形成了分子生物学技术耦合大数据分析的模式,实现了多种尺度上的关联研究。阐述了土壤微生物在分布格局和群落构建规则方面的研究进展,重点介绍了分子生物学技术和大数据分析在土壤微生物生物地理研究中的应用,对土壤微生物生物地理学未来在微生物分类分辨率、模型验证与构建和功能基因地理学的发展方向进行了展望。 Abstract:Soil harbors a huge microbial biodiversity, which plays a key role in organic matter decomposition, element biogeochemical cycles, plant productivity and biological health. Understanding the geographical distribution and the community formation and assembly rules of soil microorganisms is helpful to predict the function evolution of soil microbiome and its regulatory impact on the terrestrial ecosystem under global change scenarios. Since the 21st century, the integrated approaches of molecular biology techniques in coupling with big data analysis have been applied and various large-scale international microbial projects have been launched to promote the research of microbial biogeography. In this review, firstly we evaluate the recent development of soil microbial biogeography and the current understanding of community assembly rules. We then introduce the approaches of molecular biology techniques coupling with big data analysis. Finally, the future development of soil microbial biogeography with a specific emphasis on classification resolution, model constructions-and-validations and gene biogeography were prospected. 参考文献 相似文献 引证文献

Single and multi-objective optimization of a gearbox considering dynamic performance and assemblability

Today, most companies do not consider the assembly aspects of a product until late in the design process, and often do so in a manual way, mainly relying on the experience of the assembly engineers. This results in designs that comply with the performance requirements, but that have a suboptimal or unfeasible assembly process. This leads to design changes late in the product development process, causing significant extra costs. To solve this issue, a framework is presented, which is able to perform design optimizations considering both the assembly process and the performance of the future product, allowing trade-off analysis of the obtained solutions. The assembly process evaluation is automated with an algorithm that evaluates Design For Assembly (DFA) rules, enabling the assessment and quantitative evaluation of the ease-of-assembly of the whole product and/or individual assembly operations.The presented framework is used in the context of the design of a gearbox, in which total mass, assemblability and performance need to be optimized. The performance of the gearbox is determined by the axle‘s stiffness and first resonance frequency. The assemblability of the gearbox is evaluated based on 2 DFA rules. The first rule considers the number of unique types of standard parts used in the assembly and how they influence the complexity of the assembly process. The second rule evaluates the convenience of fastening standard parts (e.g., bolts or screws) using the corresponding tool during the assembly operation.First, the design problem is formulated as a single objective optimization in which mass and assemblability are optimized given constraints on the axle‘s stiffness and first resonance frequency. In each iteration of the optimization, a parametrized finite element model is used for the performance evaluation of the current design, while the assemblability cost estimation is based on the CAD model of the assembly. Second, a multi-objective co-optimization of the gearbox design is carried out were both performance and assemblability are optimized. By constructing the Pareto front an accurate and effective trade-off can be made between objectives of the gearbox design, which allows to reasonably choose the best design of the gearbox.

Environmental filtering and low trait redundancy characterise fish assemblages in Lake Mamo, Orinoco River floodplain, Venezuela

The study of assembly rules of fish communities in Neotropical floodplain lakes represents a major interest in community ecology due to their high species diversity and environmental variation, both spatial and temporal. In this study, assembly rules of freshwater fishes in Lake Mamo were explored. The main goals of this research were to analyse the seasonal variations in taxonomic and functional diversities of fishes in sandbanks and patches of aquatic macrophytes, in order to identify whether the fish assemblages are organised according to environmental filtering or limiting similarity, and to explore the relationships between taxonomic and functional diversity to determine if fish assemblages are either functionally redundant or complementary. In both mesohabitats, fishes were collected using seine nets during four hydrological seasons corresponding to low waters, rising waters, high waters and falling waters. Taxonomic and functional structure of fish assemblages in each habitat and across hydrological seasons was examined through multidimensional scaling (MDS), PERMANOVAs and principal co-ordinate analyses. Seasonal variations in taxonomic diversity were determined through Fligner tests of Shannon diversity indices, and for functional diversity, of functional richness (FRich), functional dispersion (FDisp), functional evenness (FEve) and functional divergence (FDiv). Null model analyses were used to determine if the functional indices diverged from randomness across hydrological seasons. Finally, relationships between functional indices and Shannon diversity were explored using linear, power, asymptotic and logistic models. There were significant differences in taxonomic and functional composition between mesohabitats and more markedly across hydrological seasons. All fish assemblages were significantly underdispersed at all instances, while functional evenness was higher than expected in both mesohabitats during low waters, signaling both a strong environmental filtering and niche packing. There were significant linear associations between the Shannon diversity and functional dispersion and between the Shannon diversity and functional evenness, suggesting that functional redundancy in these assemblages is low. In Lake Mamo, fish assemblages are filtered first by seasonality and then by habitat type. As more species are added to the assemblages, niches are more packed in the functional space, but the number of traits increases at a constant rate. This means that if a lake becomes impaired as a consequence of potential oil spills, the loss of fish species could represent also the loss of traits and functions in the ecosystem.

Engineering knowledge formalization and proposition for informatics development towards a CAD-integrated DfX system for product design

Target design methodologies (DfX) were developed to cope with specific engineering design issues such as cost-effectiveness, manufacturability, assemblability, maintainability, among others. However, DfX methodologies are undergoing the lack of real integration with 3D CAD systems. Their principles are currently applied downstream of the 3D modelling by following the well-known rules available from the literature and engineers’ know-how (tacit internal knowledge).This paper provides a method to formalize complex DfX engineering knowledge into explicit knowledge that can be reused for Advanced Engineering Informatics to aid designers and engineers in developing mechanical products. This research work wants to define a general method (ontology) able to couple DfX design guidelines (engineering knowledge) with geometrical product features of a product 3D model (engineering parametric data). A common layer for all DfX methods (horizontal) and dedicated layers for each DfX method (vertical) allow creating the suitable ontology for the systematic collection of the DfX rules considering each target. Moreover, the proposed framework is the first step for developing (future work) a software tool to assist engineers and designers during product development (3D CAD modelling).A design for assembly (DfA) case study shows how to collect assembly rules in the given framework. It demonstrates the applicability of the CAD-integrated DfX system in the mechanical design of a jig-crane. Several benefits are recognized: (i) systematic collection of DfA rules for informatics development, (ii) identification of assembly issues in the product development process, and (iii) reduction of effort and time during the design review.

Plant Sedimentary Ancient DNA From Far East Russia Covering the Last 28,000 Years Reveals Different Assembly Rules in Cold and Warm Climates

Woody plants are expanding into the Arctic in response to the warming climate. The impact on arctic plant communities is not well understood due to the limited knowledge about plant assembly rules. Records of past plant diversity over long time series are rare. Here, we applied sedimentary ancient DNA metabarcoding targeting the P6 loop of the chloroplast trnL gene to a sediment record from Lake Ilirney (central Chukotka, Far Eastern Russia) covering the last 28 thousand years. Our results show that forb-rich steppe-tundra and dwarf-shrub tundra dominated during the cold climate before 14 ka, while deciduous erect-shrub tundra was abundant during the warm period since 14 ka. Larix invasion during the late Holocene substantially lagged behind the likely warmest period between 10 and 6 ka, where the vegetation biomass could be highest. We reveal highest richness during 28–23 ka and a second richness peak during 13–9 ka, with both periods being accompanied by low relative abundance of shrubs. During the cold period before 14 ka, rich plant assemblages were phylogenetically clustered, suggesting low genetic divergence in the assemblages despite the great number of species. This probably originates from environmental filtering along with niche differentiation due to limited resources under harsh environmental conditions. In contrast, during the warmer period after 14 ka, rich plant assemblages were phylogenetically overdispersed. This results from a high number of species which were found to harbor high genetic divergence, likely originating from an erratic recruitment process in the course of warming. Some of our evidence may be of relevance for inferring future arctic plant assembly rules and diversity changes. By analogy to the past, we expect a lagged response of tree invasion. Plant richness might overshoot in the short term; in the long-term, however, the ongoing expansion of deciduous shrubs will eventually result in a phylogenetically more diverse community.

The Automated Test Assembly and Routing Rule for Multistage Adaptive Testing with Multidimensional Item Response Theory

AbstractDesigning a multidimensional adaptive test (M‐MST) based on a multidimensional item response theory (MIRT) model is critical to make full use of the advantages of both MST and MIRT in implementing multidimensional assessments. This study proposed two types of automated test assembly (ATA) algorithms and one set of routing rules that can facilitate the development of an M‐MST. Different M‐MST designs were developed based on the proposed ATA algorithms and routing rules and were evaluated through two sets of simulation studies. Study 1 used simulated item banks and considered a variety of testing factors, and results from which can inform us the theoretical performance of the proposed M‐MST designs. Study 2 was designed based on a real multidimensional assessment. In addition, a MCAT was simulated as a baseline design to demonstrate the advantage of the proposed M‐MST design in each study. Our simulation results indicate that the proposed ATA algorithms and routing rule can generate M‐MSTs with a good‐quality control and the same or even better ability estimation results than the MCAT given the same condition. This demonstrates the advantage of using M‐MST for multidimensional assessment especially for the one that needs to satisfy many nonstatistical constraints.

Microbial generalist or specialist: Intraspecific variation and dormancy potential matter.

Microbial generalists and specialists coexist in the soil environment while having distinctive impacts on microbial community dynamics. In microbial ecology, the underlying mechanisms as to why a species is a generalist or a specialist remain ambiguous. Herein, we collected soils across a national scale and identified bacterial generalists and specialists according to niche breadth at the species level (OTU level), and the single-nucleotide differences in each species were measured to investigate intraspecific variation (at zero-radius OTU level). Compared with that of the specialists, the intraspecific variation of the generalists was much higher, which ensured their wider niche breadth and lower variability. The higher asynchrony and different niche preferences of conspecific individuals and the higher dormancy potential within the generalists further contributed to their stability in varying environments. Besides, generalists were less controlled by environmental filtering, which was indicated by the stronger signature of stochastic processes in their assembly, and had higher diversification and transition rates that allowed them to adapt to environmental changes to a greater extent than specialists. Overall, this study provides a new comprehensive understanding of the rules of assembly and the evolutionary roles of bacterial generalists and specialists. It also highlights the importance of intraspecific variation and the dormancy potential in the stability of species.

Biodiversity-productivity relationship in urban vascular flora: a comparison between wild edible and non-edible plants

Background: Wild edible plants are species that are not cultivated but can be consumed as food. These plants may exhibit the highest taxonomic and phylogenetic diversity within urban floras, since they have a longer history of use associated with humans than non-edible plants. Also, because biodiversity is strongly associated with biomass, edible plants plant might show higher productivity (biomass per site) than non-edible plants. Questions: Is taxonomic and phylogenetic diversity of wild edible plants higher than non-edibles within urban areas? Is the alpha-biodiversity of wild edible plants positively related to biomass productivity in urban areas? Study sites and years of study: Cities of the coastal Mediterranean-type ecosystem, central Chile, 2015 and 2016. Methods: We characterized the taxonomic and phylogenetic diversity of urban flora differentiating wild edible and non-edible plants. Then, we assessed whether alpha-diversity of assemblages is related to their biomass productivity. Results: Both taxonomic and phylogenetic diversity were higher for edibles than non-edible plants. For edible plants, biomass was positively related to species richness and negatively with the mean phylogenetic diversity (MPD, a measure of evolutionary relationship among plants within an assemblage). Conclusions: Species richness is a suitable proxy to estimate wild edible plant diversity and their biomass in cities surpassing other proxies, such as phylogenetic diversity. Negative effect of MPD on biomass suggests that only a subgroup of related plants, possibly highly adapted to urban conditions, contribute to edible plant production. The distinction between wild edible and non-edible plants offers a better understanding of the assembly rules and biodiversity-biomass relationship within urban floras.

Functional-Structural Plant Modeling Highlights How Diversity in Leaf Dimensions and Tillering Capability Could Promote the Efficiency of Wheat Cultivar Mixtures.

Increasing the cultivated diversity has been identified as a major leverage for the agroecological transition as it can help improve the resilience of low input cropping systems. For wheat, which is the most cultivated crop worldwide in terms of harvested area, the use of cultivar mixtures is spreading in several countries, but studies have seldom focused on establishing mixing rules based on plant architecture. Yet, the aerial architecture of plants and the overall canopy structure are critical for field performance as they greatly influence light interception, plant interactions and yield. The very high number of trait combinations in wheat mixtures makes it difficult to conduct experimentations on this issue, which is why a modeling approach appears to be an appropriate solution. In this study, we used WALTer, a functional structural plant model (FSPM), to simulate wheat cultivar mixtures and try to better understand how differences between cultivars in key traits of the aerial architecture influence mixture performance. We simulated balanced binary mixtures of cultivars differing for different critical plant traits: final height, leaf dimensions, leaf insertion angle and tillering capability. Our study highlights the impact of the leaf dimensions and the tillering capability on the performance of the simulated mixtures, which suggests that traits impacting the plants' leaf area index (LAI) have more influence on the performance of the stand than traits impacting the arrangement of the leaves. Our results show that the performance of mixtures is very variable depending on the values of the explored architectural traits. In particular, the best performances were achieved by mixing cultivars with different leaf dimensions and different tillering capability, which is in agreement with numerous studies linking the diversity of functional traits in plant communities to their productivity. However, some of the worst performances were also achieved by mixing varieties differing in their aerial architecture, which suggests that diversity is not a sufficient criterion to design efficient mixtures. Overall, these results highlight the importance of simulation-based explorations for establishing assembly rules to design efficient mixtures.

Exploring Plant Functional Diversity and Redundancy of Mediterranean High-Mountain Habitats in the Apennines

We analyzed plant functional diversity (FD) and redundancy (FR) in Mediterranean high-mountain communities to explore plant functional patterns and assembly rules. We focused on three above-ground plant traits: plant height (H), a good surrogate of competition for light strategies, and specific leaf area (SLA) and leaf dry matter content (LDMC), useful indicators of resource exploitation functional schemes. We used the georeferenced vegetation plots and field-measured plant functional traits of four widely spread vegetation types growing on screes, steep slopes, snowbeds and ridges, respectively. We calculated Rao’s FD and FR followed by analysis of standardized effect size, and compared FD and FR community values using ANOVA and the Tukey post hoc test. Assemblage rules varied across plant communities and traits. The High FRH registered on snowbeds and ridges is probably linked to climatic filtering processes, while the high FDH and low FDSLA and FDLDMC on steep slopes could be related with underlying competition mechanisms. The absence of FD patterns in scree vegetation pinpoint random assembly processes which are typical of highly unstable or disturbed ecosystems. Improved knowledge about the deterministic/stochastic processes shaping species coexistence on high mountain ecosystems should help researchers to understand and predict vegetation vulnerability to environmental changes.

Global decline in capacity of coral reefs to provide ecosystem services

Global decline in capacity of coral reefs to provide ecosystem services

The impact of local assembly rules on RNA packaging in a T = 1 satellite plant virus.

The vast majority of viruses consist of a nucleic acid surrounded by a protective icosahedral protein shell called the capsid. During viral infection of a host cell, the timing and efficiency of the assembly process is important for ensuring the production of infectious new progeny virus particles. In the class of single-stranded RNA (ssRNA) viruses, the assembly of the capsid takes place in tandem with packaging of the ssRNA genome in a highly cooperative co-assembly process. In simple ssRNA viruses such as the bacteriophage MS2 and small RNA plant viruses such as STNV, this cooperative process results from multiple interactions between the protein shell and sites in the RNA genome which have been termed packaging signals. Using a stochastic assembly algorithm which includes cooperative interactions between the protein shell and packaging signals in the RNA genome, we demonstrate that highly efficient assembly of STNV capsids arises from a set of simple local rules. Altering the local assembly rules results in different nucleation scenarios with varying assembly efficiencies, which in some cases depend strongly on interactions with RNA packaging signals. Our results provide a potential simple explanation based on local assembly rules for the ability of some ssRNA viruses to spontaneously assemble around charged polymers and other non-viral RNAs in vitro.

Interspecific interactions regulate plant reproductive allometry in cereal–legume intercropping systems

Abstract Calls for the application of ecological principles in agriculture have gained momentum. Intercropping systems are designed by growing two, or more, annual crop species in the same field, aiming for a better resource use efficiency. However, assembly rules for their design are lacking. Notably, it is unknown whether species performances are maximized during both the vegetative and reproductive phases given the sensitivity of reproductive allocation rules to resource limitation. Interestingly, ecological theory provides expectations regarding putative invariance of plant reproductive allometry (PRA) under non‐limiting conditions for plant growth. Here we examined whether and how PRA changes in response to plant–plant interactions in intercropping systems, which can inform both ecological theory and the understanding of the functioning of intercropping systems. We analysed a dataset of 28 field cereal–legume intercropping trials from various climatic and management conditions across Western Europe. PRA was quantified in both mixing and single‐species situations. Plant reproductive allometry was positively impacted in specific management conditions, leading to a greater increase in yield for a given increase in plant size. Variations in PRA were more beneficial to legumes grown in unfertilized mixtures, which explains their use as a key component in actual intercropping systems. The response for cereals was similar but less pronounced in magnitude, and was greater under resource‐limiting conditions. Focusing on intercropping conditions, hierarchical competition (indicated by biomass difference between intercropped species) appears as a strong driver of the reproductive output of a given species. Synthesis and applications. Plant reproductive allometry (PRA) behaves in crop species in the same way as it does in wild species. However, contrary to theoretical expectations about an overall invariance of PRA, we highlighted taxon‐specific and context‐dependent effects of plant–plant interactions on PRA. This systematic deviation to PRA expectations could be leveraged to cultivate each species up to its reproductive optimum while accounting for the performance of the other, whether farmer's objective is to favour one species or to reach an equilibrium in seed production. Sowing density and cultivar choice could regulate the biomass of each component, with specific targets derived from allometric relationships, aiming for an optimal reproductive allocation in mixtures.

Functional Diversity and Assembly Rules of Two Deciduous Seasonal Forests in Southeastern Brazil

Abstract Deciduous seasonal forests (DSFs) have a peculiar floristic composition, with species capable of surviving periods of high water deficit in a year. Our goal was to demonstrate that abiotic filters lead to the assembly of two DSF communities that have high floristic dissimilarity. For this, we characterized the environment of the areas and used the community-weighted mean (CWM), functional richness (FRic) and functional dispersion (FDis) indices for regional recognition of functional patterns. The local assessment of assembly rules was carried out using null models. We found differences in the FRic and FDis between the areas, which was attributed to the different floristic influences exercised on the communities. However, in both, the typical attributes of dry formations were dominant (CWM), indicating that, on the regional scale of study, the dry season acts as a filter in the composition of species in the communities. On a local scale, stochastic dispersion was identified as the most influential mechanism in the assembly of communities. We conclude that deterministic and stochastic processes act in the assembly of the studied communities, and the proportion of each of these depends on the scale, with abiotic filtration predominating on a regional scale and stochastic dispersion events on a local scale.

Diversity partitioning and distance-decay relationship of saprophytic flies (Insecta: Diptera) in the western Brazilian Amazon

Studying beta-diversity patterns of biological communities and how species are organized in space is central to understanding the processes that maintain species diversity. Furthermore, knowledge on beta-diversity patterns is key for the protection and conservation planning of regional diversity. Insects represent the terrestrial animal group with the largest global biomass and a great body of information about spatial diversity patterns of megadiverse orders such as hymenopterans, lepidopterans, and coleopterans is available. However, studies dedicated to understanding these patterns in dipterans are scarce. Here, we aim to characterize the spatial variation of the assemblage of phytosaprophytic flies in the Amazon forest by investigating its distribution across hierarchies of spatial scales and the effect of geographical distance. The study site is located in the Direct Influence Area of the Belo Monte hydroelectric dam, Pará state, Brazil. Sampling followed the Rapid Assessments for Long Term Ecological Research experimental design. Fly assemblages were not uniform across most of the spatial scales investigated. The larger scale (from 10 to 100 km) contributed more to the gamma diversity of the region than the smaller ones (approximately 1 km). The beta diversity with a Shannon index of over 60 % of γ taxonomic diversity was influenced by the diversity within transects (α-diversity). Pairwise dissimilarity showed no significant relationship between geographical distance and Sorensen dissimilarity, turnover, nestedness, balanced variation in species abundances, or abundance gradient components. The absence of stochastic processes in the formation of the assemblages of phytosaprophytic flies indicates that environmental filters are more important to its structuring than neutral processes. Thus, studies on larger scales can provide more robust evidence on the assemblages distribution, both in preserved and highly impacted environments. Our study considered this wide-scale and our finding revealed some patterns in the assembly rules of the flies community Amazon.

Intraspecific trait variation drives grassland species richness and productivity under changing precipitation

AbstractIt has been increasingly recognized that plant traits and their intraspecific variation play pivotal roles in determining how ecosystem structure and function respond to a changing environment. Yet, it remains unclear how and which plant traits regulate the assembly process and thus affect ecosystem structure and function under climate changes. Here, we selected six steppe sites with snow fences along a precipitation gradient in inner Mongolia. We measured traits including plant height and leaf carbon, nitrogen, and phosphorus concentrations. We incorporated intraspecific trait variation to quantify the strength of external filters (assembly processes outside the community at a larger spatial scale), the strength of internal filters (assembly processes within the local community), and functional redundancy (the number of species having a similar function to an ecosystem). We applied these assembly rules to explain the changes in biodiversity and productivity in response to changing precipitation. We found that increased rainfall reduced plant carbon (C), nitrogen (N), and phosphorous (P) concentrations, but did not affect plant height. High snowfall increased phosphorous concentration, but did not affect other traits. Latent variable models identified climate (rainfall) and soil nutrient conditions (soil total N and P content) were more important than external filtering processes in predicting species richness. However, external filtering processes were the most important predictor of productivity. More specifically, we found with the increase in steppe productivity, the strength of the external filtering on leaf N increased and on plant height decreased, leading to leaf N converging into a small range but broadening the range of plant height. The internal filters had no significant effects on species richness or productivity. Additionally, we found that low precipitation reduced functional redundancy. We emphasize that intraspecific trait‐variation drives plant productivity and richness responses to precipitation changes by regulating community assemblage. Our finding also underlines the importance to separate the contributions of different functional traits in regulating the responses of ecosystem structure and function to climate changes.

Variation of community assembly rules of a whole turtle family (Pelomedusidae) from continental to local scales in Africa

AbstractAssessing community assembly rules has been a prominent task by community ecologists. Using a turtle family (Pelomedusidae) as a study case, we analyze the structure of their communities from the continental scale to the habitat scale, by using a suite of statistical approaches: (i) GIS modeling of the most complete presence sites dataset (from IUCN/SSC TFTSG archive); (ii) niche overlap and co‐occurrence null models with Monte Carlo simulations; (iii) generalized linear models. We used, after controlling for spatial autocorrelation, continental scale presence data totalling 1698 locality records belonging to 27 species of African Pelomedusidae and local scale data from 58 surveyed stations in eight different countries, totalling 1936 turtle individuals of at least five species (but several taxa are included into one of these “species”: the Pelomedusa subrufa complex). At the local scale, the number of co‐occurring Pelomedusidae in Africa ranged from two to three species, although the ranges of up to five total species overlapped at various locations on the continental scale. A simulation study showed that, at the continental scale, the various species co‐occurred following assembly rules that are compatible with interspecific competition by two metrics. At the habitat scale, the mean number of sympatric species was just below two and the maximum number of sympatric species per local site was three, with significant variation among habitat categories (more in forest than in any other habitat). Body size filtering may be also a mechanism that facilitates coexistence of pelomedusid species under sympatric conditions.