Deterministic processes drive turnover-dominated beta diversity of breeding birds along the central Himalayan elevation gradient

Beta diversity,the variation of community composition among sites,bridges alpha and gamma diversity and can reveal the mechanisms of community assembly through applying distance-decay models and/or partitioning beta diversity into turnover and nestedness components from functional and phylogenetic perspectives.Mountains as the most natural experiment system provide good opportunities for exploring beta diversity patterns and the underlying ecological processes.Here,we simultaneously consider distance-decay models and multiple di-mensions of beta diversity to examine spatial variations of bird communities,and to evaluate the relative importance of niche-based and neutral community assembly mechanisms along a 3600-m elevational gradient in the central Himalayas,China.Our results showed that species turnover dominates taxonomic,functional,and phylogenetic beta diversity.We observed strongest evidence of spatial distance decays in taxonomic similarities of birds,followed by its phylogenetic and functional analogues.Turnover component was highest in taxonomic beta diversity,while nestedness component was highest in functional beta diversity.Further,all correlations of assemblage similarity with climatic distance were higher than that with spatial distances.Standardized values of overall taxonomic,functional,and phylogenetic beta diversity and their turnover components increase with increasing elevational distance,while the standardized values of taxonomic and phylogenetic nestedness decreased with increasing elevational distance.Our results highlighted the niche-based deterministic processes in shaping elevational bird diversity patterns that were determined by the relative roles of decreasing trend of environmental filtering and increasing trend of limiting similarity along elevation distances.

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.

A phylogenetic approach identifies patterns of beta diversity and floristic subregions of the Qinghai-Tibet Plateau

Patterns of taxonomic and phylogenetic beta diversity and their relationships with environmental correlates can help reveal the origin and evolutionary history of regional biota.The Qinghai-Tibet Plateau(QTP)harbors an exceptionally diverse flora,however,a phylogenetic perspective has rarely been used to investigate its beta diversity and floristic regions.In this study,we used a phylogenetic approach to identify patterns of beta diversity and quantitatively delimit floristic regions on the Qinghai-Tibet Plateau.We also examined the relationships between multifaceted beta diversity,geographical distance,and climatic difference,and evaluated the relative importance of various factors(i.e.,climate,topography and history)in shaping patterns of beta diversity.Sørensen dissimilarity indices indicated that patterns of species turnover among sites dominated the QTP.We also found that patterns of both taxonomic and phylogenetic beta diversity were significantly related to geographical distance and climatic difference.The environmental factors that contributed most to these patterns of beta diversity include annual precipitation,mean annual temperature,climatic gradients and climatic instability.Hierarchical dendrograms of dissimilarity and non-metric multidimensional scaling ordination based on phylogenetic beta diversity data identified ten floristic subregions in the QTP.Our results suggest that the contemporary environment and historical climate changes have filtered species composition among sites and eventually determined beta diversity patterns of plants in the QTP.

Studying beta diversity: ecological variation partitioning by multiple regression and canonical analysis

Aims Beta diversity is the variation in species composition among sites in a geographic region.Beta diversity is a key concept for understanding the functioning of ecosystems,for the conservation of biodiversity and for ecosystem management.The present report describes how to analyse beta diversity from community composition and associated environmental and spatial data tables.Methods Beta diversity can be studied by computing diversity indices for each site and testing hypotheses about the factors that may explain the variation among sites.Alternatively,one can carry out a direct analysis of the community composition data table over the study sites,as a function of sets of environmental and spatial variables.These analyses are carried out by the statistical method of partitioning the variation of the diversity indices or the community composition data table with respect to environmental and spatial variables.Variation partitioning is briefly described herein.Important findings Variation partitioning is a method of choice for the interpretation of beta diversity using tables of environmental and spatial variables.Beta diversity is an interesting‘currency’for ecologists to compare either different sampling areas or different ecological communities cooccurring in an area.Partitioning must be based upon unbiased estimates of the variation of the community composition data table that is explained by the various tables of explanatory variables.The adjusted coefficient of determination provides such an unbiased estimate in both multiple regression and canonical redundancy analysis.After partitioning,one can test the significance of the fractions of interest and plot maps of the fitted values corresponding to these fractions.

Environment and management jointly shape the spatial patterns of plant species diversity of moist grasslands in the mountains of northeastern Yunnan

Grasslands account for about a quarter of the Earth's land area and are one of the major terrestrial ecosystems,with significant ecological and economic values.The influence of environmental factors and management types on grassland biodiversity has garnered considerable attention.This study investigated how patterns of species richness are influenced by geographical distance,environmental gradients,and management type in the moist mountain grasslands of northeastern Yunnan,China.We used structural equation modeling to disentangle the impacts of environment and management on phylogenetic community structure,and using partial Mantel tests estimated the roles of dispersal limitation and environmental filtering on taxonomic and phylogenetic beta diversity of three types of grasslands.Our results show that taxonomic alpha diversity increased in grazed grasslands and decreased in mowed grasslands,compared with protected grasslands.However,the phylogenetic structure of both grazed and mowed grassland communities was clustered,whereas that of protected communities was random.Moreover,both grazing and mowing significantly reduced the taxonomic and phylogenetic beta diversity of grasslands,with the lowest values observed in mowed grasslands.Both taxonomic and phylogenetic beta diversity were dominated by species turnover under different management types.The taxonomic and phylogenetic beta diversities of protected and grazed grasslands were simultaneously affected by environmental filtering and dispersal limitation,with the later playing a stronger role.In addition,mowing and following management measures had a stronger filtering effect on grassland community structure,as reflected by changes in community composition.

Altitudinal patterns of stand structure and herb layer diversity of Picea schrenkiana forests in the central Tianshan Mountains,Northwest China

Altitude is a useful indicator to examine patterns of forest structure and species diversity in relation to environmental factors.In this study,the altitude patterns of forest stand structure and species diversity were analyzed across 20 plots in the Tianchi Nature Reserve,Northwest China.The results showed that mean stem height（Hm）,maximum stem height（Hmax） and mean stem diameter at breast height（Dm） of Picea schrenkiana trees all decreased significantly with increasing altitude.Potential tree height（H＊） decreased while stem taper increased significantly as altitude increased,suggesting remarkable altitudinal changes in biomass allocation between the diameter and height growth of Picea schrenkiana.Understory herbaceous richness increased significantly with increasing altitude,or with decreasing total basal area（TBA）,Hm and stand volume（Volume）.High light availability for understory herbs might account for the higher species richness at high altitude.Sorensen Index decreased significantly with the increase in altitude intervals,while the Cody Index demonstrated a converse pattern,suggesting greater differences in species composition with larger distances.

Geographic patterns of taxonomic and phylogenetic β-diversity of angiosperm genera in regional floras across the world

Beta diversity(β-diversity)is the scalar between local(α)and regional(γ)diversity.Understanding geographic patterns ofβ-diversity is central to ecology,biogeography,and conservation biology.A full understanding of the origin and maintenance of geographic patterns ofβ-diversity requires exploring both taxonomic and phylogeneticβ-diversity,as well as their respective turnover and nestedness components,and exploring phylogenetic p-diversity at different evolutionary depths.In this study,we explore and map geographic patterns ofβ-diversity for angiosperm genera in regional floras across the world.We examine both taxonomic and phylogeneticβ-diversity and their constituent components,and both tip-weighted and basal-weighted phylogeneticβ-diversity,and relate them to latitude.On the one hand,our study found that the global distribution ofβ-diversity is highly heterogeneous.This is the case for both taxonomic and phylogeneticβ-diversity,and for both tip-weighted and basal-weighted phylogeneticβ-diversity.On the other hand,our study found that there are highly consistent geographic patterns among different metrics ofβ-diversity.In most cases,metrics ofβ-diversity are negatively associated with latitude,particularly in the Northern Hemisphere.Different metrics of taxonomicβ-diversity are strongly and positively correlated with their counterparts of phylogeneticβ-diversity.

The impact of earlier flood recession on metacommunity diversity of wintering waterbirds at shallow lakes in the middle and lower Yangtze River floodplain

The hydrological regime in wetlands plays an important role in the process of wintering waterbird metacommunity assemblage.However,increasing frequency of extreme climate and the intensification of human activities,such as the construction of sluices and dams,have resulted in frequently abnormal hydrological regime in the middle and lower Yangtze River floodplain.In recent years,earlier flood recession has become one of the main hydrological problems faced in the shallow lakes,having a great impact on wetland biodiversity.It is necessary to understand the impact of earlier flood recession on waterbirds,an indicator of wetland biodiversity,and the metacommunity concept is helpful to elucidate the underlying mechanism involved in the processes of assemblage by waterbird communities.In this study,we surveyed the wintering waterbirds at three sub-lakes of Caizi Lakes during 2019-2020 and 2020-2021 and compared the richness,abundance,alpha and beta diversity of waterbirds in and among local metacommunities under earlier flood recession and normal hydrological regime.The results showed that the earlier flood recession reduced the species richness in the early stage and abundance in the late stage,it also reduced the Shannon-Wiener index in the early stage and increased the dissimilarity between and within waterbird metacommunities in the late stage.The partition of beta diversity showed that the turnover component played a major role in the process of waterbird metacommunity assemblage.It was found that the earlier flood recession reduced the richness,abundance in different stages of flood recession,which also increased the turnover of waterbirds.Metacommunities with high habitat heterogeneity had better resistance to abnormal hydrological regime,which resulted in high dissimilarity between and within metacommunities.The results of this study provide important information for waterbird conservation and water level management at shallow lakes in the middle and lower Yangtze River floodplain.

Patterns of species dominance, diversity and dispersion in ‘Khasi hill sal' forest ecosystem in northeast India

Background： The ＇Khasi hill sal＇ forest ecosystem in Meghalaya, India represents the easternmost limit of sal distribution. We tested if tree diversity and compositional heterogeneity of this ecosystem was higher than other sal-dominated forests due to moister environment. Methods： Vegetation was sampled in 11 transects of 10 m width and up to 500 m length covering 5.2 ha area. All stems ≥10 cm girth at breast height were enumerated. Results： We found a pattern of mixed dominance of Shored robusta （sal） and Schima wollichii and co-dominance of Pinus kesiyo and Careya arborea. The Shannon＇s diversity index （H＇） was 3.395 nats. This value is remarkably high and competitive to that of moist sal forests of eastern Himalayan foothills and sal-dominated forests of Tripura. A high value of H＇ was manifested by： a） high species richness （S = 123）, b） good equitability （70.6%）, c） ＇fair＇ resource apportionment, and d） abundance of rare species （84% species with less than one per cent of total individuals, 67% species with two or less individuals ha-1 and 59% species with one or less individuals ha-1）. The compositional heterogeneity was ＇fair＇ （Whittaker＇sβw = 3.15）. The presence of Fagaceae with six species commanding 4.3% of importance value （IVl） and of a pine （P. kesiya） in sal forest was remarkable. As many as 58 species showed ＇low density （〈 10 individuals ha-1）, uniform dispersion＇, five species achieved ＇higher density （〉 10 individuals ha-l）, uniform dispersion＇ and six of the top 10 species were ＇clumped＇. The forest showed an exponential demographic curve illustrating ＇good＇ regeneration of an expanding community. Vertical stratification was simple with a poor canopy and fair subcanopy, which together with low basal area （15.65 m2 . ha-1 for individuals ≥ 10 cm gbh） indicated logging of mature sal trees in the past. Conclusions： The ＇Khasi hill sal＇ forest ecosystem is richer in alpha and beta diversity than most sal-dominated forests, but past logging has reduced basal area. Selective removal of small timber and firewood, slash-and-burn agriculture and recurrent burning of forest floor are the principal anthropogenic factors controlling forest structure and regeneration of species.

Influence of soil and elevation on roadside cryptogam diversity in the tropical Andes

Background: The deforestation caused by road construction is one of the main drivers for both biodiversity and function loss in tropical ecosystems. Terricolous cryptogams are pioneers in colonizing roadside and they are limited by environmental and edaphic factors, thus, cryptogams may act as pioneers for ecosystem rehabilitation at roadside.Methods: This research was aimed at determining the diversity and composition of terricolous cryptogams, as well as their relationship with elevation and soil properties among roadside of the tropical Andes of Ecuador, in order to establish indicator species of this anthropized ecosystems. Five elevations were selected and in each one 50grids of 20 cm×30 cm were sampled(250 in total along the road), where occurrence, cover and identification of every cryptogam species were recorded. To evaluate the effect of elevation and soil properties on cryptogam richness, a linear model was conducted. Species composition among elevations was compared by non-metric multidimensional scaling(NMDS), and their relationship with the environmental variables through a correlation with adjusted axes was performed. A total of 72 species were recorded, those being 44 bryophytes and 28lichens. Species richness and composition of terricolous cryptogams were influenced by elevation and soil properties, thus the richness is higher at elevations E1, E2 and E3(2600, 2200 and 1800 m a.s.l.), differing from low elevations E4 and E5(1400 and 1000 m a.s.l.). Higher elevations with specific soil conditions(e.g bulk density, nitrogen and silt) harbored different cryptogam communities than those in lower elevations.Conclusions: A combination of both elevation and soil properties are shaping the colonization by terricolous cryptogams commnunities. As such, 18 species were identified as the best indicators for all sets of environmental conditions at the roadside, which can therefore be considered for monitoring ecological processes in tropical areas. Use of biocrusts for restoration is an emerging field. If implemented in the study region, elevation and soil drivers may help to better chose the more suitable cryptogam species to manage and stabilize roadside in tropical roads.

3eta Diversity of Mbuna in Lake Malawi

Molecular and field studies suggest that Mbuna have limited migration range and are restricted by habitat discontinuities especially in areas where rocky habitats are separated by stretches of sand. This study estimated regional diversity of Mbuna in Lake Malawi. The estimated fl-diversity for all sites was 114.5 Mbuna suggesting that there was high level of allopatrism for the species complex. Sympatric index was low in the two regions of southern and northern lake and the observed high-end richness strongly correlated with minimum species richness. The sympatric index for the whole lake was 0.8, with non-monotypic species complexes showing declining values of sympatric index and the decline was dependent on the geographical scale of the area covered. The northern region sites had mean habitat ranking of 84.5% while the southern sites had habitat ranking of 56.7% supporting the observation that there are more rocky habitats in the northern part of the lake than in the southern. Implications of habitat ranking are discussed in terms of species abundance and richness.

Effect of climate and altitude on plant community composition and richness in Brazilian inselbergs

Plant communities are shaped by multiple factors along environmental gradients;however,studies are limited on how environmental filtering drives community composition and species richness on tropical inselbergs.We evaluate the influence of altitude and climatic variables related to temperature and precipitation on plant community composition and species richness on Brazilian inselbergs.We assume as a premise that both climate and altitude would induce changes on plant community composition and species richness at the local level.We used plant inventory data from 370 sampling units across four inselberg sites in the Atlantic Forest of Espírito Santo State,south-eastern Brazil.We tested the univariate and multivariate effects of altitude and climate variables on community composition and species richness with multiple models.Differences in species richness between inselbergs were evaluated using sample-based data to estimate rarefaction and extrapolation curves.In addition,differences in species composition and taxonomic beta diversity were examined via novel frequency-based metrics.A contrasting climate pattern was observed between the inselberg sites,with south sites being wet compared to the dry conditions found in northern sites.Species richness by rarefaction showed a similar pattern within regional sites;however,there were marked differences between regions.Species richness and beta diversity showed significant differences among sites,with higher values in southern sites than in northern sites.In a multi-model comparison between inselberg sites,altitude significantly influenced community composition and species richness and explained more variance than climate models.This finding suggested that climate could act to some extent on these tropical inselbergs;however,altitude was a better predictor of plant community composition and species richness at the local level.

Understanding how environmental heterogeneity and elevation drives the distribution of woody communities across vegetation types within the campo rupestre in South America

The campo rupestre sensu lato is a vegetation type that occurs in South American mountains,supports a distinctive flora characterized by high rates of endemism,high herbaceous species richness and often-neglected but also species-rich of the arboreal stratum.We aimed to investigate how environmental factors and elevation are associated with the distribution and diversity of woody species in different rupestrian vegetation types across South America.Using a database of 2,049 woody species from 185 sites across four vegetation types within the campo rupestre,we assessed how the vegetation types were grouped according to their floristic composition and number of shared indicator species,as well as by using different beta diversity indices.The most important variables from a set of 27 variables(e.g.altitude,geo-edaphic and climatic)explaining species distribution were identified using redundancy analysis(RDA)and variation partitioning methods.The distribution of vegetation types was related to both environmental and spatial fractions,with a set of 17 variables retained(e.g.rockiness,grass cover and temperature seasonality as the most important variables).There was an association between the floristic composition of each vegetation type and the elevation range.Although the identified vegetation types are floristically related,they are distinguished by exclusive and habitat-specialist woody species.This uniqueness of vegetation types should be considered in terms of complementarity for the conservation of campos rupestres.

Phylogenetic structure and phylogenetic diversity of angiosperm assemblages in forests along an elevational gradient in Changbaishan,

Aims Understanding what drives the variation in species composition and diversity among local communities can provide insights into the mechanisms of community assembly.Because ecological traits are often thought to be phylogenetically conserved,there should be patterns in phylogenetic structure and phylogenetic diversity in local communities along ecological gradients.We investigate potential patterns in angiosperm assemblages along an elevational gradient with a steep ecological gradient in Changbaishan,China.Methods We used 13 angiosperm assemblages in forest plots(32×32 m)distributed along an elevational gradient from 720 to 1900 m above sea level.We used Faith’s phylogenetic diversity metric to quantify the phylogenetic alpha diversity of each forest plot,used the net relatedness index to quantify the degree of phylogenetic relatedness among angiosperm species within each forest plot and used a phylogenetic dissimilarity index to quantify phylogenetic beta diversity among forest plots.We related the measures of phylogenetic structure and phylogenetic diversity to environmental(climatic and edaphic)factors.Important Findings Our study showed that angiosperm assemblages tended to be more phylogenetically clustered at higher elevations in Changbaishan.This finding is consistent with the prediction of the phylogenetic niche conservatism hypothesis,which highlights the role of niche constraints in governing the phylogenetic structure of assemblages.Our study also showed that woody assemblages differ from herbaceous assemblages in several major aspects.First,phylogenetic clustering dominated in woody assemblages,whereas phylogenetic overdispersion dominated in herbaceous assemblages;second,patterns in phylogenetic relatedness along the elevational and temperature gradients of Changbaishan were stronger for woody assemblages than for herbaceous assemblages;third,environmental variables explained much more variations in phylogenetic relatedness,phylogenetic alpha diversity and phylogenetic beta diversity for woody assemblages than for herbaceous assemblages.

Relationship between species richness,taxonomic distinctness,functional diversity,and local contribution toβdiversity and effects of habitat disturbance in the riparian spider community of the Ganga River,India

Background In the riverine riparian ecosystem,particularly in India,the knowledge of the effects of habitat disturbance on taxonomic distinctness,functional diversity,and local contribution toβdiversity(LCBD)of spider community is elusive.The present study examined the relationships between the index of taxonomic distinctness(Δ^(+)),index of variation in taxonomic distinctness(λ^(+)),functional evenness(FEve),functional divergence(FDiv),functional dispersion(FDis),and LCBD of spider community of the Ganga River and the effects of habitat disturbance on these indices.A total of 27 sampling sites were selected along the bank of the Ganga River.Based on the rating of the disturbance scores,the sites were classified into lowly,moderately,and highly disturbed sites.To understand the relationships between species richness,Δ^(+),λ^(+),FDis,FDiv,FEve,LCBD,and habitat disturbance score,Pearson’s correlation was calculated,followed by the linear regression model.The one-way multivariate analysis of variance was used to find differences in taxonomic distinctness and functional diversity in the different disturbed sites.Results Significant relationships were found betweenλ^(+)andΔ^(+),FDis andΔ^(+),FDis andλ^(+),FDiv and species richness,FEve and species richness,FEve andλ^(+),FEve and habitat disturbance,LCBD and FEve,and LCBD and habitat disturbance.A significant difference was present in the indices of functional diversity between the lowly,moderately,and highly disturbed sites.Agriculture,garbage dump,human settlement,and created embankment influenced the spider community’sλ^(+),FEve,and LCBD.Conclusion Unrestrained anthropogenic activities exacerbate habitat disturbance by affecting ecological processes.Thus,understanding linkages between ecosystem disturbance,taxonomic,functional,andβdiversity can be fundamental to managing and conserving natural resources.This work highlights the importance of including taxonomic and functional diversity to comprehend the impact of habitat disturbance on riverine riparian spiders beyond just the number of species.An integrated taxonomic and functional diversity approach coupled withβdiversity can be used to support environmental assessment,restoration,and conservation planning of the biological resources of the Ganges River.

Fish diversity reduction and assemblage structure homogenization in lakes:A case study on unselective fishing in China

Unselective fishing involves activities that target the entire assemblage rather than specific fish species,size classes,or trophic levels.This common fishing approach has been in practice for decades in inland waters in China but its implications for biodiversity remain unclear.We addressed this issue by studying fish assemblages in freshwater lakes(five fishing lakes,one reference lake,and a total of 51 sampling sites)between pre-and postfishing time-periods in Eastern China during 2017–2019.The effects of lake,fishing period,and their interactions on fish abundance,biomass,and diversity indices were assessed.Multivariate analysis was conducted to test for differences in fish assemblages among lakes and between fishing periods.After the implementation of fishing activities,significant reductions in fish species richness,abundance,biomass,and all three life-history strategies(opportunistic,equilibrium,and periodic)were observed in fishing lakes,whereas opposite trends were observed in the reference lake.Compositional similarity of fish assemblages among fishing lakes increased over the threeyear monitoring period.Our results suggest that unselective fishing reduces fish diversity and homogenizes fish assemblage structure in lakes.These findings have important implications for protecting both biodiversity and fisheries in inland waters in China and are applicable to other countries or regions that rely on fish as a major food source.

Taxonomic, functional, and phylogenetic diversity patterns reveal different processes shaping river fish assemblages in the Eastern Huai River Basin, China

Understanding contributions of different environmental drivers to the structure and function of river biota is critical for biodiversity and environmental conservation.Yet,there is no consensus on which drivers have the greatest impact on fish diversity,especially in watersheds disturbed by multiple human activities.Fish taxonomic,phylogenetic,and functional diversity at both alpha and beta dimensions and their environmental drivers were studied in a total of 84 river sites from three watersheds,Huai River watershed(HRW),Sui River watershed(SRW),and Yishusi River watershed(YRW)in the Eastern Huai River Basin of China.Results showed that rivers in the three watersheds had no significant difference in both taxonomic and functional alpha diversity.Rivers in the HRW had significantly higher phylogenetic alpha diversity.For taxonomic and phylogenetic beta diversity,the overall beta diversity and turnover component were significant higher in the HRW.For functional beta diversity,the overall beta diversity was significantly lower in the HRW.Multiple linear regression(MLR)and redundancy analysis(RDA)showed that local(e.g.,nutrients,dissolved oxygen,river width,transparency),regional(e.g.,wetland),climate(e.g.,temperature),and spatial variables structured alpha and beta fish diversity.Variation partitioning analysis indicated that the pure contributions of local and spatial variables were more important than that of climate and regional variables,which suggested that spatial effects and local environmental filtering were the main factors driving the beta diversity of fish assemblages in these rivers.The current study highlights the importance of considering multidimensional diversity and multiple environmental factors for conserving river fishes.

Structure,variation and assembly processes of bacterial communities in different root-associated niches of tomato under periodic drought and nitrogen addition

Root-associated bacteria play a vital role in the growth and adaptation of host plants to drought stress.These bacteria can be classified as rhizoplane and rhizosphere bacteria based on their distance from the root surface.Tomato plants are often exposed to periodic drought and nitrogen(N)addition throughout their life cycle,but the impacts of these factors on the plant and root-associated bacteria are not well understood.To gain insight into this relationship,we conducted an experiment to monitor the effects of periodic drought and N addition on rhizoplane and rhizosphere bacteria of tomato plants.Drought and N addition had interactive effects on plant and soil properties,which varied with the timing of drought.There were clear divergences in community traits such as alpha diversity,beta diversity,and network topological features between the two types of bacteria.The rhizoplane bacteria showed lower alpha diversity but higher beta diversity and were more sensitive to drought and N addition than the rhizosphere bacteria.Nitrogen addition could downsize the effects of drought on rhizoplane bacterial community compositions.The higher proximity to the root might induce a community to develop more cooperation between different members to cope with plant metabolites,as revealed by the more connected and modularized community network of the rhizoplane bacteria.Drought at the seedling stage had great legacy effects on plant and soil properties.It may enhance selection,cause the dominance of deterministic processes in the assembly of rhizoplane bacteria,and reduce bacterial community network complexity.In conclusion,N addition could interact with drought in affecting tomato plants and their root-associated bacteria,depending on the timing of drought and the fineness of root niches.The higher sensitivity of rhizoplane bacteria to drought and N addition calls for more research due to their higher proximity and importance to plants in future environmental changes.

Contrasting effects of space and environment on functional and phylogenetic dissimilarity in a tropical forest

Aims The evolutionary history and functional traits of species can illumi-nate ecological processes supporting coexistence in diverse forest communities.However,little has been done in decoupling the rela-tive importance of these mechanisms on the turnover of phylogenetic and functional characteristics across life stages and spatial scales.Therefore,this study aims to estimate the contribution of environment and dispersal on the turnover of phylogenetic and functional diversity across life stages and spatial scales,in order to build a coherent pic-ture of the processes responsible for species coexistence.Methods We conducted the study in Xishuangbanna Forest Dynamics Plot in Yunnan Province,southwest China.We used four different spatial point process models to estimate the relative importance of disper-sal limitation and environmental filtering.The functional traits and phylogenetic relationships of all individual trees were incorporated in the analyses to generate measures of dissimilarity in terms of pair-wise and nearest-neighbor phylogenetic and functional characteris-tics across life stages and spatial scales.Important Findings We found non-random patterns of phylogenetic and functional turnover across life stages and spatial scales.Environmental filtering structured pairwise phylogenetic and functional beta diversity across spatial scales,while dispersal limitation alone,and in combination with environment filtering,shaped nearest neighbor phylogenetic and functional beta diversity.The relative importance of dispersal limitation and environmental filtering appeared to change with life stage but not with spatial scale.Our findings suggest that phylogenetic and functional beta diversity help to reveal the ecological processes responsible for evolu-tionary and functional assembly and highlight the importance of using a range of different metrics to gain full insights into these processes.

A taxonomic and phylogenetic perspective on plant community assembly along an elevational gradient in subtropical forests

Aims Biodiversity patterns along elevational gradients have been well documented.Yet,the variations of biodiversity patterns along elevations and their underlying mechanisms are still unclear.Integrating multiple facets of biodiversity provides novel insights into the mechanisms for driving community assembly.In this study,species abundance information was incorporated into taxonomic and phylogenetic diversity to reveal the ecological and evolutionary forces of plant community assembly along an elevational gradient in subtropical forests.Methods We selected 17 woody plant plots along an elevational gradient from 270 to 1470 m in eastern China’s subtropical forests.Both presence-based and abundance-based measures of angiosperm species were used to quantify taxonomic alpha diversity,phylogenetic alpha diversity,phylogenetic relatedness,as well as taxonomic and phylogenetic dissimilarity among these plots.And the relations between these measures and climatic and topographic variables were analyzed.Important Findings For both abundance-weighted and unweighted measures,we observed an overall increasing pattern for taxonomic alpha diversity along elevation,and distance-decay trends of taxonomic and phylogenetic similarity with increased elevational distances.However,there were disparity patterns of phylogenetic alpha diversity between abundance-weighted and unweighted measures.For phylogenetic structure,there was no significant trend along elevation.Both topographical and microclimatic variables were main drivers of diversity patterns and phylogenetic structure.Compared with unweighted measures,abundance-weighted measures were strongly related with the slope and stand basal area.Overall,our results prove that deterministic processes mediated by local species abundance imprint on plant community composition along the elevational gradient.