Positive interactions can produce species-rich communities and increase species turnover through time

Aims The process of facilitation,where a species increases the survival,growth,and fitness of another species,is becoming increasingly recognized as a critical factor in shaping the structure of plant communities.This process is particularly important in stressful environments.Yet few studies have attempted to incorporate positive interactions into community ecological theories such as the neutral theory of biodiversity.Here,we use an equalizing trade-off model as a foundation to study the potential impact of facilitation on species richness and community temporal turnover.Methods Based on a spatially explicit birth–death trade-off model,we assume that the occurrence of facilitation is dependent on the presence of interspecific neighbours.We further propose that the realized birth rate for a given individual subject to facilitation is proportional to the number of interspecific neighbours within its neighbourhood.Thus,in our model,the individuals of rare species will benefit more from the existence of heterospecific individuals than common species.Important Findings As the facilitative coefficient increased,the species richness for simulated communities at the dynamically stochastic equilibrium was also increasing.Simulations also demonstrated that facilitation could increase the replacement of species through time:communities with facilitation become more dissimilar(i.e.have smaller Bray–Curtis similarity values)than communities without or with a lower degree of facilitation after the same time interval.Facilitation from interspecific neighbours on rare species increased their population sizes and consequently made them less prone to extinction,thus enhancing species richness.Meanwhile,in a saturated community,with the increase of species richness,mean population size of entire communities decreased,making species more prone to extinction on average,and thus increased the community temporal turnover.Our results suggest that future experimental work on the effect of facilitation on community-level properties should focus not just on species richness but also on other descriptors of community dynamics such as the temporal species turnover.

Patterns of species richness and beta diversity of vascular plants along elevation gradient in Brazilian páramo

Understanding the relationships between plant diversity and the environment is an important step towards conservation of species and ecosystems.In this study,we hypothesize that community species richness decreases and species composition change along the elevation gradient,with a greater contribution of species turnover than nestedness to beta diversity.We surveyed plant species in 300 plots(1 m×1 m)in four elevational bands(2100 m,2300m,2500 m,and 2700 m)in the CaparaóNational Park,Southeastern Brazil.The samples presented a great number of species(97 spp.,59 genera,27families),however,74%of the species were considered rare with their relative abundance being<1%.Among the four bands along the gradient,we detected two distinct communities with few species in common.The transition between the two communities occurred at 2500 m,and this elevation band also had the highest species richness in total.A non-metric multidimensional scaling(NMDS)showed floristic differences between the bands even though they had similar richness.In 89%of the plot pairs,using pairwise comparison of species composition,only half of the species that occurred in one did occur in the other plot.The dissimilarity among the plots and elevational band reflects a significant contribution of spatial species turnover to the species richness and beta diversity on the Caparaómountain.Beta diversity increased with spatial scale(from plot to elevational-band).The dissimilarity(βSOR=0.907)in the area was due almost exclusively to spatial species turnover(βSIM=0.879),with very low contribution of species nestedness(βSNE=0.028).Our research showed that species richness does not decrease with elevation in the study area,but the floristic composition changes.The clear distinction of species along the gradient show that spatial species turnover is the major diversitygenerating process in the studied area.

Quantifying multiple-site compositional turnover in an Afrotemperate forest, using zeta diversity

Background： Species turnover is typically measured by partitioning diversity components into alpha and pairwise beta diversity. However, alpha and beta components cannot express the full spectrum of multiple-site compositional turnover. To this end, zeta diversity has been proposed as an extended framework to allow complete biodiversity partitioning and to measure multiple-site species turnover. We use a zeta-diversity framework to explore the turnover and potential community assembly processes of an African Montane Forest. Methods： Using a 20 m grid, we explore the species turnover in a 4.55 ha forest plot located in the Garden Route National Park of South Africa, with 47 and 27 canopy and sub-canopy tree species in the regional poo We first calculate how zeta diversity declines and how the probability of retention of species with particular occupancies changes with increasing zeta orders （i.e. the number of sites [grid cells] involved in the calculation）. Using null models with row sums and column sums constrained respectively, we explore whether species turnover is driven by mechanisms of ecological differences （species-specific occupancies） or habitat heterogeneity （site-specific alpha diversity and thus environmental filters）. Results： The decline of zeta diversity with zeta order followed a power law; that is, the probability of retention increased with species occupancies, suggesting common species being more likely to be discovered in extra sites. The null model retaining row sums （species＇ occupancy） of the species-by-site matrix recreated perfectly the decline of zeta diversity, while the null model of habitat heterogeneity （retaining column sums） was rejected. This suggests that mechanisms driving species-specific occupancies （i.e. ecological differences between species） dictate the multi-site species turnover in the community. The spatial patterns of zeta diversity revealed little spatial structuring forces, supporting a fine-grain structure in these southern Cape forests. Conclusions： The framework of zeta diversity revealed mechanisms driving the large discrepancies in the occupancy among species that are behind the species turnover in the African Montane forest plot. Future studies could further link species turnover to spatial distance decay. Environmental filters and temporal turnover from landscape demography could bring a cohesive understanding of community assembly in these unique forest ecosystems.

Life forms affect beta-diversity patterns of larch forests in China

Beta-diversity reflects the spatial changes in community species composition which helps to understand how communities are assembled and biodiversity is formed and maintained. Larch(Larix) forests, which are coniferous forests widely distributed in the mountainous and plateau areas in North and Southwest China, are critical for maintaining the environmental conditions and species diversity. Few studies of larch forests have examined the beta-diversity and its constituent components(species turnover and nestedness-resultant components). Here, we used 483 larch forest plots to determine the total betadiversity and its components in different life forms(i.e., tree, shrub, and herb) of larch forests in China and to evaluate the main drivers that underlie this beta-diversity. We found that total betadiversity of larch forests was mainly dependent on the species turnover component. In all life forms,total beta-diversity and the species turnover component increased with increasing geographic, elevational, current climatic, and paleoclimatic distances. In contrast, the nestedness-resultant component decreased across these same distances. Geographic and environmental factors explained 20%-25% of total beta-diversity, 18%-27% of species turnover component, and 4%-16% of nestedness-resultant component. Larch forest types significantly affected total beta-diversity and species turnover component. Taken together, our results indicate that life forms affect beta-diversity patterns of larch forests in China, and that beta-diversity is driven by both niche differentiation and dispersal limitation. Our findings help to greatly understand the mechanisms of community assemblies of larch forests in China.

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.

Shared-role of vegetation types,elevation and soil affecting plant diversity in an old-tropical mountain hotspot

Despite the exceptional species richness and endemism,the environmental drivers of plant diversity along old tropical mountains remain underexplored.The respective importance of vegetation types,elevation,slope,and soil to drive diversity across life-forms is poorly addressed.Here,we tested whether environmental variables drove local and regional plant diversity along an old tropical mountain according to the three main life-forms:graminoids,herbaceous and woody species.We sampled all Angiosperm species on 180 plots across five elevations,at the tropical old-mountain region of Serra do Cipó,South-eastern Brazil.We assessed soil,slope,and vegetation types,and calculated richness and beta-diversity,applying generalized least square models,linear mixed-models and partial Mantel tests to test for relationships.Richness of graminoids and herbaceous species increased with greater elevation and more nutrient-impoverished soils,while woody richness showed the inverse pattern.Beta-diversity was primarily driven by species turnover,correlated with elevation and soil and higher in less dominant vegetation types,with unique species.Despite the limited elevational range in these old mountains,it still played an important role in filtering woody species,while fostering graminoid and herbaceous species.Conservation and restoration actions need to foster the high regional diversity supported by the old mountain heterogeneous landscape and the diversity of life-forms,especially the dominant and highly diverse grassy component.

Linking changes of forage production and digestibility with grassland community assembly under nitrogen enrichment

Background:Forage production is the fundamental ecosystem service of grasslands.Although forage consumption occurs at community level,most studies focused on species-level changes of forage quality.The quantitative and qualitative changes of forage production are driven by species-specific trait,intra-specific plasticity,and species turnover.We examined the changes in forage production and digestibility after 5-year factorial treatments of nitrogen(N)addition and mowing in a temperate steppe and linked such changes to community assembly under the Price equation framework.Results:Nitrogen addition significantly reduced species richness,increased forage production,but did not change forage digestibility(indicated by the total Ca+Mg concentrations).Mowing did not affect forage production and digestibility.The positive effects of N addition on forage production were driven by the enhancement of abundance of the remaining species following N enrichment,rather than by species loss or species gain.The species identity effects could offset the effects of species richness loss or gain on forage production and digestibility.Conclusions:Our results highlight the importance of a community perspective in addressing the quantitative and qualitative changes of forage production under global change pressure of N enrichment.Species identity is important in determining the contribution of different processes of community assembly to ecosystem services.

Environmental variables vis-a-vis distribution of herbaceous tracheophytes on northern sub-slopes in Western Himalayan ecotone

Background:In the northern hemisphere,the north face of the mountains has a high diversity of species which is attributed to the moist and shady conditions at the north face.Other environmental variables may also influence the species diversity on the northern faces of the mountain and therefore needs to be studied in detail.The northern slopes represent three different sub-slopes—north,north east,and north west.During the current investigation of Pir-Panjal and Dauladhar ranges in Bhadarwah valley,fine-scale studies on the relationship between vegetation and four variables(soil pH,moisture content,electrical conductivity,and steepness)were conducted.The study determined the role of these variables on the vegetation of three different sub-slopes.The sampling was done at the confluence of two communities(forest and grassland)at three sites on the northern sub-slopes of the lesser stratum in western Himalayan.Results:The result revealed that rich herbaceous diversity prevails on the lesser Himalayan stratum(Bhadarwah valley).As many as 65.8%species differ from site to site,whereas species commonality among the sites is minimum.The role of environmental variables on the species composition at different sub-slopes of the north mountain face is deduced through canonical correspondence analysis(CCA).Conclusions:The availability of solar light increases air and soil temperature on the north east–facing slope.All the environmental variables(soil pH,moisture,electrical conductivity,and mountain steepness)are insignificant at pure north face for the species composition.Therefore,it can be concluded that some other environmental variables may influence the species composition which are needed to be further investigated.

Contrasting beta diversity of spiders,carabids,and ants at local and regional scales in a black soil region,northeast China

Understanding the factors determining the formation of each community and metacommunity across a landscape is one of the most important ideas in soil animal ecology.However,the variables and parameters that shape soil arthropod communities in agroecosystems have not been resolved.These arthropods can serve as important bioindicators of field management and its sustainability.We sampled five com plantations in each of three locations across a region spanning 600 km to come up with these determinants of the community structure of ground-dwelling spiders(Erigoninae:Araneae),carabids(Coleoptara:Carabidae),and ants(Hymenoptera:Formicidae).The analysis of the five fields within each of the three locations represent our local-scale samples,while the comparisons of the 15 sites across all three locations represent the regional scale samples.We tested the hypothesis that in the models we sampled,environmental/soil variables would drivecommunity assembly locally(within location comparisons),but at the regional scale(between location comparisons),climatic and spatial variables would drive metacommunity assembly.The outcomes of our study showed distinct communities at each of the three locations when compared across regions but locally,fields were similar in species composition,as expected.Locally,spatial variables were important but not soil variables,regulated species richness and abundance.Turnover contributed more than nestedness to explain the biodiversity of spiders,carabids,and ants at both the local and regional scales.Neither purely climate variables,nor purely soil or spatial variables were significant enough explanations for the regional scale arthropod community composition.However,spatially structured environmental factors contributed most to explain the patterns supporting our hypothesis.We conclude that biodiversity in this agroecosystem area can be promoted by a mosaic of land uses being encouraged to increase landscape complexity at the regional scale.

Vegetation stability during the last two centuries on the western Tibetan Plateau:a palynological evidence

Investigating the dynamics of vegetation is an essential basis to know how to protect ecological environments and to help predict any changes in trend.Because of its fragile alpine ecosystem,the Tibetan Plateau is a particularly suitable area for studying vegetation changes and their driving factors.In this study,we present a high-resolution pollen record covering the last two centuries extracted from Gongzhu Co on the western Tibetan Plateau.Alpine steppe is the predominant vegetation type in the surrounding area throughout the past 250 years with stable vegetation composition and abundance,as revealed by pollen spectra dominated by Artemisia,Ranunculaceae,Cyperaceae,and Poaceae.Detrended canonical correspondence analysis(DCCA)of the pollen data reveals low turnover in compositional species(0.41 SD),suggesting that the vegetation in the Gongzhu catchment had no significant temporal change,despite climate change and population increases in recent decades.We additionally ran DCCA on ten other pollen records from the Tibetan Plateau with high temporal resolution(1-20 years)covering recent centuries,and the results also show that compositional species turnover(0.15-0.81 SD)is relatively low,suggesting that the vegetation stability may have prevailed across the Tibetan Plateau during recent centuries.More high-resolution pollen records and high taxonomic-resolution palaeo-vegetation records(such as sedaDNA),however,are needed to confirm the vegetation stability on the Tibetan Plateau.