Patterns and drivers of avian taxonomic and phylogenetic beta diversity in China vary across geographical backgrounds and dispersal abilities

Geographical background and dispersal ability may strongly influence assemblage dissimilarity;however,these aspects have generally been overlooked in previous large-scale beta diversity studies.Here,we examined whether the patterns and drivers of taxonomic beta diversity(TBD)and phylogenetic beta diversity(PBD)of breeding birds in China vary across(1)regions on both sides of the Hu Line,which demarcates China’s topographical,climatic,economic,and social patterns,and(2)species with different dispersal ability.TBD and PBD were calculated and partitioned into turnover and nestedness components using a moving window approach.Variables representing climate,habitat heterogeneity,and habitat quality were employed to evaluate the effects of environmental filtering.Spatial distance was considered to assess the impact of dispersal limitation.Variance partitioning analysis was applied to assess the relative roles of these variables.In general,the values of TBD and PBD were high in mountainous areas and were largely determined by environmental filtering.However,different dominant environmental filters on either side of the Hu Line led to divergent beta diversity patterns.Specifically,climate-driven species turnover and habitat heterogeneity-related species nestedness dominated the regions east and west of the line,respectively.Additionally,bird species with stronger dispersal ability were more susceptible to environmental filtering,resulting in more homogeneous assemblages.Our results indicated that regions with distinctive geographical backgrounds may present different ecological factors that lead to divergent assemblage dissimilarity patterns,and dispersal ability determines the response of assemblages to these ecological factors.Identifying a single universal explanation for the observed pattern without considering these aspects may lead to simplistic or incomplete conclusions.Consequently,a comprehensive understanding of large-scale beta diversity patterns and effective planning of conservation strategies necessitate the consideration of both geographical background and species dispersal ability.

Global comparisons of beta diversity among mammals,birds,reptiles,and amphibians across spatial scales and taxonomic ranks

Beta diversity is the change in species composition among areas in a geographic region. The proportion of species shared between two areas often decreases when the distance separating them increases, leading to an increase in beta diversity. This study compares beta diversity among four classes of terrestrial vertebrates （mammals, birds, reptiles, and amphibians） at both regional （biogeographic realm） and global extents, using the same sets of faunal sample units for all four groups in each comparison. Beta diversity is lower for the two endothermic taxa （birds and mammals） than for the two ectothermic taxa （reptiles and amphibians） in all six biogeographic realms examined. When the four taxa in the six biogeographic realms are combined, beta diversity at the species rank is higher than that of the genus rank by a factor of 1.24, and is higher than that of the family rank by a factor of 1.85. The ratio of beta diversity at the genus rank to that at the family rank is 1.50. Beta diversity is slightly higher for ecoregions of 5000-99,999 km^2 than for ecoregions of 100,000-5,000,000 km^2.

Fish gut microecosystem: a model for detecting spatial pattern of microorganisms

The spatial distribution pattern of organisms is a basic issue in understanding the mechanisms of community assembly. Although the spatial distributions of animals and plants have been well studied,those of microorganisms are still being debated. In this study, we used a fi sh gut microecosystem to detect the spatial pattern of microbes, because it can provide a relatively unifi ed and stable environment. Results suggest that the turnover of intestinal bacterial assemblages showed a weak but highly signifi cant negative correlation between similarity and distances in the microbial community, in respect of both grass carp intestinal loci distances and the geographical distance between fi sh sampling sites. Our results also suggest that intestinal bacterial assemblages responded to differences within the external environment and within different parts of the fi sh themselves. These results show that some, or possibly all, microbes are restricted in their distribution and that environmental factors are also important infl uences on the structure of intestinal bacterial assemblages. The fi sh gut microecosystem is useful in promoting study of the spatial distribution patterns of microorganisms.

Conspecific negative density dependence in American beech

Background： One of the most important drivers of forest biodiversity is conspecific negative density dependence（CNDD）, a reduction in performance when conspecific densities are high. While the majority of CNDD research has focused on tropical forests, evidence is mounting that CNDD may also play an important role in temperate forests.To further explore the potential reach of this phenomenon, we investigated CNDD in American beech（Fagus grandifolia）in a mature mid-Atlantic forest.Methods： We used bivariate point pattern analyses to examine spatial relationships between large beech trees and conspecific saplings, and we also contrasted these patterns with comparable patterns for heterospecifics. In addition, to address the possibility of dispersal limitation and the associated effects on spatial patterns, we analyzed seedling density as a function of adult conspecific abundance.Results： We found that beech saplings were more repel ed from large conspecifics than large heterospecifics, despite the fact that beech seedling density was positively correlated with beech basal area. However, saplings of other canopy tree species were also repel ed from adult beech trees, suggesting a general suppressive effect. Nonetheless, the discrepancy between beech seedling and sapling densities beneath adult conspecifics suggests that beech seedling survival rates were reduced in vicinity of conspecific adults.Conclusions： Regardless of the extent to which beech inhibits heterospecific trees, a negative effect on conspecific recruits may be critical for biodiversity maintenance. Without this conspecific suppression, a dense layer of shade-tolerant beech saplings could form beneath adult beech trees. If this were to occur, beech would have a substantial head-start fol owing canopy disturbance, and this late-successional species could potential y dominate a stand in perpetuity,through repeated disturbance cycles.

Dispersion Limit for IM/DD Fiberoptic Transmission Systems

A general formula for the dispersion limit of single-mode-fiber IM/DD (Intensity Modulation /Direct Detection) systems is derived for arbitrary given normalized pulse width P, eye opening penalty X and source linewidth enchancement factor α. From the comparison with published theoretical results, computer simulation and experimental data, its validity and convenience in system design and evaluation are shown. Using this simple and general formula, one can easily obtain the dispersion limit of various fiber types under different working conditions in IM/DD systems.

Seed dispersal and seedling recruitment of trees at different successional stages in a temperate forest in northeastern China

spatial distribution of adult trees in a forest community is determined by patterns of both seed dispersal and seedling recruitment.the objectives of our study were to understand the processes of seed dispersal and seedling recruitment of dominant tree species in a temperate forest of northeastern China and to identify the factors constraining seed dispersal and seedling establishment at different stages of forest succession.Methods During three summer and autumn sessions between 2006 and 2008,altogether 113080 seeds from 22 different tree species were collected in three large field plots representing different for-est types in the Changbai mountain region of northeastern China.the spatial distribution of seed abundance was analyzed using a syrjala test.regeneration success of nine major tree species was assessed using variables defining‘limitations’in‘seeds’and‘seed-ling establishment’.Important Findings We found that seed production fluctuated between years and varied greatly with forest types.Four tree species,Acer spp.,Fraxinus man-dshurica,Tilia amurensis and Betula spp.,had the greatest seed pro-duction and the widest range of seed dispersal,whereas Quercus mongolica showed the most sustained seed production pattern.the spatial patterns of seed abundance differed significantly among forest types and years.the tree species investigated in this study differed in the degree of seed limitation,as well as in limitation of seedling establishment.there were both negative and positive correlations between seed density and seedling density,depending on site and parental tree density.seeds of 16 tree species were found in the Populus davidiana-Betula platyphylla forest(PbF)plot,11 in the conifer and broad-leaved mixed forest(CbF)plot but only 8 in the broad-leaved-Korean pine mixed forest(bKF)plot.the number of seed-contributing species was not only greater in the secondary forests(CbF and PbF plots)than in the primary forest(bKF plot)but was also more variable during the 3 years of assessment.results from the correlations between seed density and seedling occurrence and that between parental tree density or seed weight and dispersal limitation confirm our intuitive expectations,i.e.heavy seeds had greater dispersal limitation but higher establishment success than light seeds.

Assembly processes underlying bacterial community differentiation among geographically close mangrove forests

Bacterial communities play pivotal roles in nutrient cycling in mangrove forests.The assembly of mangrove microbial communities has been found to be influenced by complex factors,such as geographic distance,physicochemical conditions,and plant identity,but the relative importance of these factors and how these factors shape the assembling process remain elusive.We analyzed the bacterial communities sampled from three mangrove species(Aegiceras corniculatum,Bruguiera sexangula,and Kandelia obovata)at three locations along the estuarine Dongzhai Harbor in Hainan,China.We revealed larger differences in rhizosphere bacterial communities among geographical locations than among plant species,indicated by differences in diversity,composition,and interaction networks.We found that dispersal limitation and homogeneous selection have substantial contributions to the assembly of mangrove rhizosphere bacterial communities in all three locations.Following the phylogenetic‐bin‐based null model analysis(iCAMP)framework,we also found dispersal limitation and homogeneous selection showing dominance in some bins.The greater differences among geographic locations may be mainly attributed to the larger proportions of dispersal limitation even at such a short geographic distance.We also found that beta diversity was positively correlated with environmental distances,implying that the more similar environmental conditions(such as rich carbon and nitrogen contents)among plant species may have shaped similar bacterial communities.We concluded that the geographic distances,which are associated with dispersal limitation,played a key role in assembling mangrove rhizosphere bacterial communities,while physicochemical conditions and plant identity contributed less.

Topographic species-habitat associations of tree species in a heterogeneous tropical karst seasonal rain forest, China

Aims Tropical and subtropical karst forests of south China are under increas-ing pressure from over-exploitation causing widespread habitat degra-dation and biodiversity loss.Previous research has demonstrated that topography,as a proxy for resource availability,plays an important role in shaping tree species distributions in tropical forests.However,the association between growth stages and habitats types has not been considered in this analysis.Our aim was to examine the differences among different habitat types to determine whether tree species show similar species-habitat associations at young and mature life stages.Methods We used multivariate regression tree analysis to examined species-habitat associations among eight topographically defined habitats.The results were tested with a torus-translation test and canonical correspondence analysis(CCA)for 74 species in a 15 ha karst tropi-cal seasonal rain forest at the Nonggang National Natural Reserve in south China.We considered two life stages(young and mature)of trees species that showed a positive association with topography.Important Findings We found marked differences in community characteristics and number of associations among the eight habitats.Of the 74 species subjected to torus-translation test,63 had significant positive and 70 had significant negative associations with one or more of the eight habitats.Positive associations were more frequent in higher elevation habitats and negative associations were more frequent in lower eleva-tion habitats.This suggests that edaphic and hydrological variation related to topography play important roles in habitat partitioning in heterogeneous karst forests.For the 63 tree species with significant positive associations to at least one habitat,40 of them had the same positive association at young and mature life stages.The CCA revealed that the six topographic variables considered had consistent relation-ships with species distribution among all individuals and their two life stages.This indicates that most of the karst forest tree species show consistent associations with a single habitat throughout their life.We conclude that niche differentiation plays an important role in main-taining the diversity of this heterogeneous species-rich karst forest.

The spatial variation of soil bacterial community assembly processes affects the accuracy of source tracking in ten major Chinese cities

Urban soils harbor billions of bacterial cells and millions of species.However,the distribution patterns and assembly processes of bacterial communities remain largely uncharacterized in urban soils.It is also unknown if we can use the bacteria to track soil sources to certain cities and districts.Here,Illumina MiSeq sequencing was used to survey soil bacterial communities from 529 random plots spanning 61 districts and 10 major cities in China.Over a 3,000 km range,community similarity declined with increasing geographic distance(Mantel r=0.62),and community composition was clustered by city(R^(2)=0.50).Within cities(<100 km),the aforementioned biogeographic patterns were weakened.Process analysis showed that homogenizing dispersal and dispersal limitation dominated soil bacterial assembly at small and large spatial scales,respectively.Accordingly,the probabilities of accurately tracking random soil sources to certain cities and districts were 90.0% and 66.7%,respectively.When the tested samples originated from cities that were more than 1,265 km apart,the soil sources could be identified with nearly 100% accuracy.Overall,this study demonstrates the strong distance-decay relationship and the clear geographic zoning of urban soil bacterial communities among cities.The varied importance of different community assembly processes at multiple spatial scales strongly affects the accuracy of microbial source tracking.

Point process models, the dimensions of biodiversity and the importance of small-scale biotic interactions

Aims Recent mechanistic explanations for community assembly focus on the debates surrounding niche-based deterministic and dispersalbased stochastic models.This body of work has emphasized the importance of both habitat filtering and dispersal limitation,and many of these works have utilized the assumption of species spatial independence to simplify the complexity of the spatial modeling in natural communities when given dispersal limitation and/or habitat filtering.One potential drawback of this simplification is that it does not consider species interactions and how they may influence the spatial distribution of species,phylogenetic and functional diversity.Here,we assess the validity of the assumption of species spatial independence using data from a subtropical forest plot in southeastern China.Methods We use the four most commonly employed spatial statistical models—the homogeneous Poisson process representing pure random effect,the heterogeneous Poisson process for the effect of habitat heterogeneity,the homogenous Thomas process for sole dispersal limitation and the heterogeneous Thomas process for joint effect of habitat heterogeneity and dispersal limitation—to investigate the contribution of different mechanisms in shaping the species,phylogenetic and functional structures of communities.Important Findings Our evidence from species,phylogenetic and functional diversity demonstrates that the habitat filtering and/or dispersal-based models perform well and the assumption of species spatial independence is relatively valid at larger scales(50×50 m).Conversely,at local scales(10×10 and 20×20 m),the models often fail to predict the species,phylogenetic and functional diversity,suggesting that the assumption of species spatial independence is invalid and that biotic interactions are increasingly important at these spatial scales.

Environmental and spatial contributions to seedling and adult tree assembly across tropical,subtropical and subalpine elevational gradients

Aims Quantifying the relative importance of the mechanisms that drive community assembly in forests is a crucial issue in community ecol-ogy.The present study aims to understand the ways in which niche-based and spatially based processes influence community assembly in areas in different climatic conditions and how these processes change during the transition from seedling to adult.Methods In this study,we investigated how taxonomic and phylogenetic beta diversity in seedling and adult stages of forest trees change across three elevational transects in tropical,subtropical and subalpine for-ests in Southwest China,and the relationships of these changes to the environment and inter-site distances.We quantified the relative contribution of environmental conditions and spatial distribution to taxonomic and phylogenetic beta diversity of both seedling and adult life stages along each elevational transect.We also quantified the taxonomic and phylogenetic similarity between seedlings and adult trees along elevations.Important Findings Taxonomic and phylogenetic beta diversity of both seedlings and adult trees increased with an increase in both environmental distance and spatial distance in all three transects.On both taxonomic and phylo-genetic levels,the effects of environmental filtering and spatial dispos-ition varied between life stages and among forest types.Phylogenetic similarity between seedlings and adult trees increased with elevation,although the taxonomic similarity did not show clear elevational pat-terns.Our results suggest that the relative contribution of niche-based and space-based processes to taxonomic and phylogenetic assem-blages varies across major plant life stages and among forest types.Our findings also highlight the importance of ontogenetic stages for fully understanding community assembly of long-lived tree species.

Drivers of microbial beta-diversity in wastewater treatment plants in China

As one of the most well-documented biogeographic patterns,the distance-decay relation-ship provides insights into the underlying mechanisms driving biodiversity distribution.Al-though wastewater treatment plants(WWTPs)are well-controlled engineered ecosystems,this pattern has been seen among microbial communities in activated sludge(AS).However,little is known about the relative importance of environmental heterogeneity and dispersal limitation in shaping AS microbial community across China;especially they are related to spatial scale and organism types.Here,we assessed the distance-decay relationship based on different spatial scales and microbial phylogenetic groups by analyzing 132 activated sludge(AS)samples across China comprising 3,379,20016S rRNA sequences.Our results in-dicated that the drivers of distance-decay pattern in China were scale-dependent.Microbial biogeographic patterns in WWTPs were mainly driven by dispersal limitation at both local and national scales.In contrast,conductivity,SRT,and pH played dominant roles in shaping AS microbial community compositions at the regional scale.Turnover rates and the drivers of beta-diversity also varied with microorganism populations.Moreover,a quantitative re-lationship between dispersal limitation ratio and AS microbial turnover rate was generated.Collectively,these results highlighted the importance of considering multiple spatial scales and micro-organism types for understanding microbial biogeography in WWTPs and pro-vided new insights into predicting variations in AS community structure in response to environmental disturbance.

Upper range limit establishment after wildfire of an obligateseeding montane forest tree fails to keep pace with 20th century warming

Aims How species respond to climate change at local scales will depend on how edaphic and biological characteristics interact with species physiological limits and traits such as dispersal.Obligate seeders,those species that depend on fire for recruitment,have few and epi-sodic opportunities to track a changing climate envelope.in such cases,long-distance seed dispersal will be necessary to take advan-tage of rare recruitment opportunities.We examine recruitment patterns and seedling growth below,at and above the timberline of an obligate-seeding Australian montane forest tree(Eucalyptus delegatensis)after stand-replacing fire,and place these changes in the context of regional warming.Methods We use two methods to detect whether E.delegatensis can estab-lish and persist above the timberline after stand-replacing wildfire in montane forests in south-east Australia.First,we examine estab-lishment patterns by using belt transects at six sites to quantify how changes in post-fire recruit density with increasing distance above the timberline seven years post-fire.Second,to determine whether dispersal or physiological constraints determine post-fire establish-ment patterns,we transplanted seedlings and saplings into bare ground above(100 m elevation),at,and below(50 m elevation)timberline 18-months after fire.We monitored seedling growth and survival for one growing season.Important Findings There was minimal upslope migration of the species after fire with most saplings observed near seed-bearing timberline trees,with only occasional outpost saplings.Transplanted seedlings and saplings sur-vived equally well across one growing season when planted above existing timberlines,relative to saplings at or below the timberline.Seedling and sapling growth rates also did not differ across these location,although seedlings grew at much faster rates than saplings.These findings suggest that upslope growing season conditions are unlikely to limit initial range expansion of trees after fire.instead,it is more likely that seed traits governing dispersal modulate responses to environmental gradients,and global change more generally.

Trends in single trait dispersion between early-mid successional stages:the importance of species pool extension and habitat scale

Aims Are there trends of increasing/decreasing dispersion of single,cat-egorical traits related to early/late-successional species between stages of community development?If yes,are these trends depend-ent on species pool extension and habitat scale?Is there a consist-ent reduction in single trait convergence or divergence in any seral stage when scaling down from ecological to local species pool?Methods Presence of all vascular species rooted within plots of 5×5 m was recorded in assemblages of exposed mining spoils(EMS)and heath-lands(HTL),which form a chronosequence on two abandoned ore tailing heaps located close to each other in the south-eastern Carpathians(Romania).Fifteen nominal,trait attributes of plant species co-occurring in the two seral assemblages were collected from available databases and subsequently classified as either suc-cessionally‘pioneer’or‘mature’.The strength of single trait conver-gence or divergence was estimated by comparison with null plant assemblages at patch type(meta-community)level by reference to the ecological or local species pool,and at community level.Important Findings At patch type level,all pioneer and mature trait attributes(apart from short life span),with significant variation between the two seral stages,increased and,respectively,decreased in dispersion irrespective of species pool extension.However,these trends were more conspicuous when using the ecological species pool,very likely due to relaxation in abiotic filtering and dispersal limitation.At community level,no consistent trends were observed between EMS and HTL assemblages,probably because most trait attributes were sorted by microenvironmental filters displaying high variation,like topography or habitat patch geometry.In both seral stages,there was a general weakening of trait convergence or divergence at patch type level when scaling down from the ecological to the local species pool,which was due to niche space contraction.At community level,there was a trend of rise in dispersion of pioneer attributes along the observed chronosequence,presumably imput-able to increasing competition for light and underground water,but an opposite trend of dispersion drop in mature attributes was not so evident.Based on these findings,we proposed two rules of thumb concerning the expected changes in dispersion of trait attributes at patch level along successions and between levels of species pool extension.In conclusion,trends in the successional dynamics of pioneer and mature trait dispersion are clearly detectable at meta-community level,especially by reference to the ecological species pool.Habitat scale and species pool extension are key factors to consider and report when estimating the magnitude of single trait dispersion.

Trait-based filtering from the regional species pool into local grassland communities

Aims For plants to establish in a local community from a pool of possible colonizers from the region,it must pass through a series of filters.Which of the filters is most important in this process has been much debated.In this study,we explored how species are filtered from the regional species pool into local communities.the aim was to determine if differences in species abundance and functional traits could explain which species from the regional species pool estab-lish at the local scale and if the filtering differed between grassland communities.Methods this study took place in a cultivated landscape in southeastern sweden.We estimated plant species abundance in 12 ex-arable field sites and 8 adjacent seminatural grassland sites and in a 100-m radius around the center of each site.We used monte Carlo simula-tions to examine if species abundance and functional traits(height,seed mass,clonal abilities,specific leaf area and dispersal method)controlled the filtering of species from the regional pool into local communities.Important Findingson average,only 28%of species found in the regional pool established in the ex-arable field sites and 45%in the seminatural grassland sites,indicating that the size of the regional species pool was not limiting local richness.For both grassland types,species abundance in the regional pool was positively correlated with species occurrence at the local scale.We found evidence for both species interaction filtering and dispersal limitation influencing the local assembly.both local and regional processes were thus influencing the filtering of species from the regional species pool into local communities.In addition,the age of the communities influenced species filtering,indicating that community assembly and the importance of different filters in that process change over succession.

Exogenous and endogenous determinants of spatial aggregation patterns in tibetan Plateau meadow vegetation

Aims We aim to quantify the relative importance of various endogenous and exogenous processes influencing the spatial distribution of the individuals of plant species at different temporal and spatial scales in a species-rich and high-cover meadow in the eastern tibetan Plateau.Methods We calculated green’s index of dispersion to infer the spatial dis-tribution patterns of 73 herbaceous species at two scales(0.25 and 1.0 m2).We constructed a series of generalized linear models to test the hypotheses that different species traits such as mean plant stem density,per capita dry biomass,maximum plant height and mean seed mass contribute to their spatial distribution.We used the first principal component of soil C,N and P to explain abundance vari-ation across quadrats and sub-plots.Important Findingsthe individuals of the species studied were highly spatially aggregated.at both spatial scales,biomass and stem density explained the most variation in aggregation,but there was no evidence for an effect of mean seed mass on aggregation intensity.the effects of soil carbon,nitrogen and phosphorus at different depths affected plant abundance mostly at the broader spatial scale.our results demonstrate that self-thinning and habitat heterogeneity all contribute to determine the spatial aggregation patterns of plant individuals in alpine meadow vegetation in the eastern tibetan Plateau.

Habitat fragmentation alters predator satiation of acorns

Aims Acorn weevils(Curculio spp.),endoparasitic granivorous insects,impede recruitment of fagaceous trees,and in turn affect community structure and ecosystem functioning.Previous studies have made considerable progress in elucidating local factors that contribute to seed predation by acorn weevils,but it is still not clear how habitat configurations interplay with local factors in influencing Curculio predation.In this study,we assessed the roles of crop size,landscape configurations(area and isolation)and their interactions on the predation rate of seeds by acorn weevils.Methods We studied acorn weevils feeding on the seeds of Castanopsis sclerophylla(Fagaceae)on two peninsulas and nine islands with varying areas and isolation levels in the Thousand-island Lake in Chun’an County,Zhejiang Province of China.Overall,crop size was estimated for 130 trees and predation status was assessed for 26207 seeds from these trees during two years.Generalized linear mixed models were performed to clarify how island area and isolation interplayed with crop size to determine predation rate on a single tree.Important Findings A negative relationship was detected between crop size and seed predation rate,indicating predator satiation at the tree level.This suggests that acorn weevils tend to stay sedentary once they have arrived at a suitable habitat.Habitat fragmentation had significant effects on seed predation such that predation rate was higher on larger,less isolated islands.Furthermore,the relationship between crop size and predation rate was significantly changed by both island area and isolation.This finding highlighted that the effects of habitat isolation might be overlooked relative to those of habitat loss.

DISSIPATION AND DISPERSION APPROXIMATION TO HYDRODYNAMICAL EQUATIONS AND ASYMPTOTIC LIMIT

The compressible Euler equations with dissipation and/or dispersion correction are widely used in the area of applied sciences, for instance, plasma physics, charge transport in semiconductor devices, astrophysics, geophysics, etc. We consider the compressible Euler equation with density-dependent （degenerate） viscosities and capillarity, and investigate the global existence of weak solutions and asvmototic limit.

Optimal Configuration of Dispersion Compensation Modules with Installation Limits

Selecting a cost optimum subset of discrete-value dispersion compensation modules (DV-DCMs) subject to maximum module count from an available set of DV-DCMs is a NP-hard problem. We derive a novel dynamic programming algorithm with pseudo-polynomial time bound and show that DV-DCM cost re-scaling can improve the running time.

SEMICLASSICAL LIMIT TO THE GENERALIZED NONLINEAR SCHR?DINGER EQUATION

In this paper, we investigate the semiclassical limit of the generalized nonlinear Schrdinger equation for initial data with Sobolev regularity. Also, we will analyze the structure of the fluid dynamical system with quantum effect corresponding to the semiclassical limit of the generalized nonlinear Schrdinger equation.