松嫩平原破碎化羊草草甸退化演替系列植物多样性的空间格局

物种多样性格局是国际生物多样性科学前沿领域热点问题.本文以松嫩平原破碎化羊草草甸退化演替系列(6种植物群落、144个斑块)为研究对象,系统地探讨了其α、β和γ多样性空间格局及其机理.结果表明:在羊草草甸退化演替系列中共发现87种植物,但没有一种能分布于所有斑块;羊草+鸡儿肠群落或羊草群落的α、β和γ多样性较高,多稀有种和特有种;碱地肤群落最低,少稀有种,无特有种;γ多样性与α多样性显著正相关,但与β多样性无相关性.各植物群落的α多样性与单个斑块面积呈显著幂函数关系,β多样性(相似性指数Sjk)仅羊草+鸡儿肠群落呈显著幂函数关系;斑块平均面积和总面积与α、γ多样性呈显著正相关,与β多样性无相关性.群落的物种丰富度越高,稀有种和特有种就越多,物种在局域斑块上灭绝的可能性越大;β多样性在物种多样性格局中的重要性与生境破碎化程度有关.     

西南喀斯特地貌区两栖动物丰富度分布格局与环境因子的关系

物种丰富度分布格局的成因机制一直是宏观生态学研究的热点问题之一。中国西南地区喀斯特地貌区(以广西、云南和贵州为主)是世界上面积最大的喀斯特地貌区, 也是全球范围内34个生物多样性热点地区之一。为了解该区域两栖动物物种丰富度分布格局及其与环境因子之间的关系, 本研究根据中国科学院成都生物研究所标本馆、中国科学院昆明动物研究所标本馆、广西壮族自治区自然博物馆和中南林业科技大学动物标本室收藏的标本数据, 以及公开发表的文献数据, 共获得18,246条两栖动物记录(219个物种), 然后运用生态位模型估测每个物种的潜在分布区, 并把每个物种的潜在分布区叠加起来, 最终得到该区域在10 km ´10 km生态位模型空间尺度上的两栖物种丰富度地理分布格局图, 最后进行多元回归和模型选择分析。结果表明: 有12种两栖动物仅在喀斯特地貌区分布, 占物种总数的5.48%; 有104种两栖动物仅在非喀斯特地貌区分布, 占物种总数的47.49%; 有103种两栖动物在喀斯特地貌区和非喀斯特地貌区均有分布, 占物种总数的47.03%; 两栖动物物种丰富度随纬度的增高而降低; 地貌类型(喀斯特地貌和非喀斯特地貌)对两栖动物物种丰富度的分布格局有显著影响(χ² = 36.47, P < 0.0001), 但模型拟合效果差(McFadden’s Rho square = 0.0037)。影响该区域两栖动物物种丰富度分布格局最大的环境因子是年均降雨量(R² = 0.232, P < 0.001), 其次是最干月平均降雨量(R² = 0.221, P < 0.001)。该区域两栖动物物种丰富度的格局主要是由地貌和不同的环境因子共同相互作用的结果, 不过仍有相当一部分物种丰富度的分布格局未被解释。因此, 要更全面地认识该区域两栖动物物种丰富度格局的形成机制, 有必要加强干扰、捕食、竞争等其他生物因子的影响研究。     

From plots to islands: species diversity at different scales

Aim To investigate how plant diversity of whole islands (‘gamma’) is related to alpha and beta diversity patterns among sampling plots within each island, thus exploring aspects of diversity patterns across scales. Location Nineteen islands of the Aegean Sea, Greece. Methods Plant species were recorded at both the whole‐island scale and in small 100 m² plots on each island. Mean plot species richness was considered as a measure of alpha diversity, and six indices of the ‘variation’‐type beta diversity were also applied. In addition, we partitioned beta diversity into a ‘nestedness’ and a ‘replacement’ component, using the total species richness recorded in all plots of each island as a measure of ‘gamma’ diversity. We also applied 10 species–area models to predict the total observed richness of each island from accumulated plot species richness. Results Mean alpha diversity was not significantly correlated with the overall island species richness or island area. The range of plot species richness for each island was significantly correlated with both overall species richness and area. Alpha diversity was not correlated with most indices of beta diversity. The majority of beta diversity indices were correlated with whole‐island species richness, and this was also true for the ‘replacement’ component of beta diversity. The rational function model provided the best prediction of observed island species richness, with Monod’s and the exponential models following closely. Inaccuracy of predictions was positively correlated with the number of plots and with most indices of beta diversity. Main conclusions Diversity at the broader scale (whole islands) is shaped mainly by variation among small local samples (beta diversity), while local alpha diversity is not a good predictor of species diversity at broader scales. In this system, all results support the crucial role of habitat diversity in determining the species–area relationship.     

The diversity field of New World leaf‐nosed bats (Phyllostomidae)

Aim To analyse how the patterns of species richness for the whole family Phyllostomidae determine the structure of diversity fields (sets of species‐richness values) within the ranges of individual bat species. Location The range of the family Phyllostomidae in North and South America. Methods We generated a database of the occurrence of 143 phyllostomid bat species in 6794 quadrats, analysing the species‐richness frequency distribution for all sites, and for subsets of sites defined by the geographic ranges of species. Range–diversity plots, depicting simultaneously the size and the mean species richness of ranges, were built to explore the patterns of co‐occurrence in widespread and restricted species. We compared the empirical patterns against two null models: (1) with scattered (non‐cohesive) ranges, and (2) with cohesive ranges modelled with the spreading‐dye algorithm. Diversity fields were analysed with richness maps for individual species and with comparisons of species‐richness frequency distributions. Results Overall richness frequency distribution showed a multimodal pattern, whereas simulated distributions showed lower values of variance, and were unimodal (for model 1) and bimodal (for model 2). Range–diversity plots for the empirical data and for the cohesive‐ranges simulation showed a strong tendency of species to co‐occur in high‐diversity sites. The scattered‐ranges simulation showed no such tendency. Diversity fields varied according to idiosyncratic features of species generating particular geographic patterns and richness frequency distributions. Main conclusions Phyllostomid bats show a higher level of co‐occurrence than expected from null models. That tendency in turn implies a higher variance in species richness among sites, generating a wider species‐richness frequency distribution. The diversity field of individual species results from the size, shape and location of ranges, but also depends on the general pattern of richness for the whole family.     

Hierarchical partitioning of ant diversity: implications for conservation of biogeographical diversity in arid and semi‐arid areas

Aim The scale of observation is important in detecting the spatial variation of biological assemblages, which should be taken into consideration for an appropriate plan of biogeographical conservation. We investigated whether (1) World Wildlife Fund’s ecoregion units are the appropriate scale for conserving ant diversity in Iran, (2) each ecoregion represents a distinct ant community composition and (3) patterns of diversity partitioning differ among four ecoregions. Location Iran, a sampling transect along four arid and semi‐arid ecoregions. Methods We applied hierarchical partitioning to data collected from a nested sampling design including four hierarchical levels: ‘local’, ‘landscape’, ‘ecoregional’ and ‘whole‐region’. Observed alpha and beta diversity components were compared with values of null distributions. Hierarchical cluster analysis was applied to evaluate similarity of ant species composition among ecoregions. Results Partitioning of whole‐region species richness showed that 85% of the species richness was generated by beta diversity among ecoregions and landscapes. The highest value of diversity was generated by beta diversity among ecoregions. Unlike whole‐region partitioning, separate partitioning within each ecoregion revealed that beta component among localities contributed to species richness of each ecoregion. Ecoregions showed different patterns of diversity partitioning. The alpha component contributed largely to the total diversity of two ecoregions, but for two other ecoregions, beta component contributed more than alpha component. Cluster analysis identified four discrete ant species compositions; however, it split landscapes of one ecoregion into two distinct groups. Main conclusions Whole‐region diversity partitioning indicates that ecoregions represent the appropriate scale for conserving ant diversity and that each ecoregion has a distinct ant fauna. However, different conservation strategies should be considered for different ecoregions owing to the differing scales of variation within them. Boundaries of ecoregions remain a subject for further studies. The influence of climate change on ecoregional boundaries should be considered and should be predicted with respect to future conservation maps.     

Type and spatial structure of distribution data and the perceived determinants of geographical gradients in ecology: the species richness of African birds

Aim Studies exploring the determinants of geographical gradients in the occurrence of species or their traits obtain data by: (1) overlaying species range maps; (2) mapping survey‐based species counts; or (3) superimposing models of individual species’ distributions. These data types have different spatial characteristics. We investigated whether these differences influence conclusions regarding postulated determinants of species richness patterns. Location Our study examined terrestrial bird diversity patterns in 13 nations of southern and eastern Africa, spanning temperate to tropical climates. Methods Four species richness maps were compiled based on range maps, field‐derived bird atlas data, logistic and autologistic distribution models. Ordinary and spatial regression models served to examine how well each of five hypotheses predicted patterns in each map. These hypotheses propose productivity, temperature, the heat–water balance, habitat heterogeneity and climatic stability as the predominant determinants of species richness. Results The four richness maps portrayed broadly similar geographical patterns but, due to the nature of underlying data types, exhibited marked differences in spatial autocorrelation structure. These differences in spatial structure emerged as important in determining which hypothesis appeared most capable of explaining each map's patterns. This was true even when regressions accounted for spurious effects of spatial autocorrelation. Each richness map, therefore, identified a different hypothesis as the most likely cause of broad‐scale gradients in species diversity. Main conclusions Because the ‘true’ spatial structure of species richness patterns remains elusive, firm conclusions regarding their underlying environmental drivers remain difficult. More broadly, our findings suggest that care should be taken to interpret putative determinants of large‐scale ecological gradients in light of the type and spatial characteristics of the underlying data. Indeed, closer scrutiny of these underlying data — here the distributions of individual species — and their environmental associations may offer important insights into the ultimate causes of observed broad‐scale patterns.     

From diversity indices to community assembly processes: a test with simulated data

Ecological theory suggests that spatial distribution of biodiversity is strongly driven by community assembly processes. Thus the study of diversity patterns combined with null model testing has become increasingly common to infer assembly processes from observed distributions of diversity indices. However, results in both empirical and simulation studies are inconsistent. The aim of our study is to determine with simulated data which facets of biodiversity, if any, may unravel the processes driving its spatial patterns, and to provide practical considerations about the combination of diversity indices that would produce significant and congruent signals when using null models. The study is based on simulated species’ assemblages that emerge under various landscape structures in a spatially explicit individual‐based model with contrasting, predefined assembly processes. We focus on four assembly processes (species‐sorting, mass effect, neutral dynamics and competition colonization trade‐off) and investigate the emerging species’ distributions with varied diversity indices (alpha, beta and gamma) measured at different spatial scales and for different diversity facets (taxonomic, functional and phylogenetic). We find that 1) the four assembly processes result in distinct spatial distributions of species under any landscape structure, 2) a broad range of diversity indices allows distinguishing between communities driven by different assembly processes, 3) null models provide congruent results only for a small fraction of diversity indices and 4) only a combination of these diversity indices allows identifying the correct assembly processes. Our study supports the inference of assembly processes from patterns of diversity only when different types of indices are combined. It highlights the need to combine phylogenetic, functional and taxonomic diversity indices at multiple spatial scales to effectively infer underlying assembly processes from diversity patterns by illustrating how combination of different indices might help disentangling the complex question of coexistence.     

Spatial turnover in the global avifauna

Despite its wide implications for many ecological issues, the global pattern of spatial turnover in the occurrence of species has been little studied, unlike the global pattern of species richness. Here, using a database on the breeding distributions of birds, we present the first global maps of variation in spatial turnover for an entire taxonomic class, a pattern that has to date remained largely a matter of conjecture, based on theoretical expectations and extrapolation of inconsistent patterns from different biogeographic realms. We use these maps to test four predictions from niche theory as to the form that this variation should take, namely that turnover should increase with species richness, towards lower latitudes, and with the steepness of environmental gradients and that variation in turnover is determined principally by rare (restricted) species. Contrary to prediction, we show that turnover is high both in areas of extremely low and high species richness, does not increase strongly towards the tropics, and is related both to average environmental conditions and spatial variation in those conditions. These results are closely associated with a further important and novel finding, namely that global patterns of spatial turnover are driven principally by widespread species rather than the restricted ones. This complements recent demonstrations that spatial patterns of species richness are also driven principally by widespread species, and thus provides an important contribution towards a unified model of how terrestrial biodiversity varies both within and between the Earth's major land masses.     

Beta‐diversity of central European forests decreases along an elevational gradient due to the variation in local community assembly processes

Beta‐diversity has been repeatedly shown to decline with increasing elevation, but the causes of this pattern remain unclear, partly because they are confounded by coincident variation in alpha‐ and gamma‐diversity. We used 8795 forest vegetation‐plot records from the Czech National Phytosociological Database to compare the observed patterns of beta diversity to null‐model expectations (beta‐deviation) controlling for the effects of alpha‐ and gamma‐diversity. We tested whether β‐diversity patterns along a 1200 m elevation gradient exclusively depend on the effect of varying species pool size, or also on the variation of the magnitude of community assembly mechanisms determining the distribution of species across communities (e.g. environmental filtering, dispersal limitation). The null model we used is a novel extension of an existing null‐model designed for presence/absence data and was specifically designed to disrupt the effect of community assembly mechanisms, while retaining some key features of observed communities such as average species richness and species abundance distribution. Analyses were replicated in ten subregions with comparable elevation ranges. Beta‐diversity declined along the elevation gradient due to a decrease in gamma‐diversity, which was steeper than the decrease in alpha‐diversity. This pattern persisted after controlling for alpha‐ and gamma‐diversity variation, and the results were robust when different resampling schemes and diversity metrics were used. We conclude that in temperate forests the pattern of decreasing beta‐diversity with elevation does not exclusively depend on variation in species pool size, as has been hypothesized, but also on variation in community assembly mechanisms. The results were consistent across resampling schemes and diversity measures, thus supporting the use of vegetation‐plot databases for understanding patterns of beta‐diversity at the regional scale.     

Geographic range, turnover rate and the scaling of species diversity

The study of the relative roles of local and regional processes in determining the scaling of species diversity is a very active field in current ecology. The importance of species turnover and the species‐range‐size frequency distributions in determining how local and regional species diversity are linked has been recognised by recent approaches. Here we present a model, based on a system of fully nested sampling quadrats, to analyse species diversity at several scales. Using a recursive procedure that incorporates increasingly smaller scales and a multiplicative formula for relating local and regional diversity, the model allows the simultaneous depiction of alpha, beta and gamma diversity in a single “species‐scale plot”. Species diversity is defined as the number of ranges that are intersected by sampling quadrats of various sizes. The size, shape and location of individual species ranges determine diversity at any scale, but the average point diversity, measured at hypothetical zero‐area localities, is determined solely by the size of individual ranges, regardless of their shape and location. The model predicts that if the species‐area relationship is a power function, then beta diversity must be scale invariant if measured at constant scale increments. Applying the model to the mammal fauna of four Mexican regions with contrasting environmental conditions, we found that: 1) the species‐range‐size frequency distribution at the scale of the Mexican regions differs from the log‐normal pattern reported for the national and continental scales. 2) Beta diversity is not scale‐invariant within each region, implying that the species‐area relationship (SAR) does not follow a power function. 3) There is geographic variation in beta diversity. 4) The scaling of diversity is directly linked to patterns of species turnover rate, and ultimately determined by patterns in the geographic distribution of species. The model shows that regional species diversity and the average distribution range of species are the two basic data necessary to predict patterns in the scaling of species diversity.     

Urbanization promotes the loss of seasonal dynamics in the semi-natural grasslands of an East Asian megacity

The biodiversity of agricultural landscapes has been noticeably affected by rapid urbanization. Although many studies have examined species diversity per unit area (alpha diversity), knowledge about the patterns of species turnover (beta diversity) in urban areas remains limited. Furthermore, most beta diversity studies have focused on spatial heterogeneity; however, losses of temporal heterogeneity resulting from urbanization remain limited. In this study, we examined how urbanization is associated with decreases in the seasonal heterogeneity of species composition, which could be used as an indicator of the loss of seasonality by ecologists and policy makers aiming to conserve biodiversity. We investigated (1) changes in species richness based on seasonal averages (alpha diversity) and (2) the seasonal turnover of species composition (beta diversity) for flowering plants and butterflies along a rural-urban gradient in semi-natural grasslands. The response variables were alpha and beta diversity for flowering plants and butterflies, and the explanatory variables were urban areas within a 1-km radius of the center of each site. Increasing urban area caused both the seasonal alpha and beta diversity of flowering plants and butterflies to decline. These results supported the homogenization hypothesis for the seasonality of plants and butterflies in semi-natural grasslands of dominant urban areas in East Asia. Future studies should focus on investigating how urbanization is causing both declines in seasonality and changes in the spatial heterogeneity of species composition and associated biodiversity loss. Ecologists and policy makers should focus on developing strategies to halt the loss of temporal biological heterogeneity to maintain biodiversity.     

Connecting species’ geographical distributions to environmental variables: range maps versus observed points of occurrence

Connecting the geographical occurrence of a species with underlying environmental variables is fundamental for many analyses of life history evolution and for modeling species distributions for both basic and practical ends. However, raw distributional information comes principally in two forms: points of occurrence (specific geographical coordinates where a species has been observed), and expert-prepared range maps. Each form has potential short-comings: range maps tend to overestimate the true occurrence of a species, whereas occurrence points (because of their frequent non-random spatial distribution) tend to underestimate it. Whereas previous comparisons of the two forms have focused on how they may differ when estimating species richness, less attention has been paid to the extent to which the two forms actually differ in their representation of a species’ environmental associations. We assess such differences using the globally distributed avian order Galliformes (294 species). For each species we overlaid range maps obtained from IUCN and point-of-occurrence data obtained from GBIF on global maps of four climate variables and elevation. Over all species, the median difference in distribution centroids was 234 km, and median values of all five environmental variables were highly correlated, although there were a few species outliers for each variable. We also acquired species’ elevational distribution mid-points (mid-point between minimum and maximum elevational extent) from the literature; median elevations from point occurrences and ranges were consistently lower (median −420 m) than mid-points. We concluded that in most cases occurrence points were likely to produce better estimates of underlying environmental variables than range maps, although differences were often slight. We also concluded that elevational range mid-points were biased high, and that elevation distributions based on either points or range maps provided better estimates.     

Modelling the occurrence of threatened plant species in taiga landscapes: methodological and ecological perspectives

Aim Understanding the spatial patterns of species distribution and predicting the occurrence of high biological diversity and rare species are central themes in biogeography and environmental conservation. The aim of this study was to model and scrutinize the relative contributions of climate, topography, geology and land‐cover factors to the distributions of threatened vascular plant species in taiga landscapes in northern Finland. Location North‐east Finland, northern Europe. Methods The study was performed using a data set of 28 plant species and environmental variables at a 25‐ha resolution. Four different stepwise selection algorithms [Akaike information criterion (AIC), Bayesian information criterion (BIC), adaptive backfitting, cross selection] with generalized additive models (GAMs) were fitted to identify the main environmental correlates for species occurrences. The accuracies of the distribution models were evaluated using fourfold cross‐validation based on the area under the curve (AUC) derived from receiver operating characteristic plots. The GAMs were tentatively extrapolated to the whole study area and species occurrence probability maps were produced using GIS techniques. The effect of spatial autocorrelation on the modelling results was also tested by including autocovariate terms in the GAMs. Results According to the AUC values, the model performance varied from fair to excellent. The AIC algorithm provided the highest mean performance (mean AUC = 0.889), whereas the lowest mean AUC (0.851) was obtained from BIC. Most of the variation in the distribution of threatened plant species was related to growing degree days, temperature of the coldest month, water balance, cover of mire and mean elevation. In general, climate was the most powerful explanatory variable group, followed by land cover, topography and geology. Inclusion of the autocovariate only slightly improved the performance of the models and had a minor effect on the importance of the environmental variables. Main conclusions The results confirm that the landscape‐scale distribution patterns of plant species can be modelled well on the basis of environmental parameters. A spatial grid system with several environmental variables derived from remote sensing and GIS data was found to produce useful data sets, which can be employed when predicting species distribution patterns over extensive areas. Landscape‐scale maps showing the predicted occurrences of individual or multiple threatened plant species may provide a useful basis for focusing field surveys and allocating conservation efforts.     

中国壳斗科植物空间多样性格局研究

采用地理信息系统技术,制作空间分布图、从空间上计算多样性格局指数,研究中国壳斗科植物属、种的空间多样性分布格局。结果显示,云南南部、广西北部和广东北部的属、种数量均较多,是中国壳斗科植物多样性的重要分布地区,甘肃南部、陕西南部、河南西部及南部是壳斗科植物向南、向北扩散的重要通道;从多样性指数来看,种的多样性指数值均比属的值高,但均匀度指数却是属的值高;当属或种的数量为1时,其所占面积、占景观的比例、斑块数量、最大斑块指数、景观形状指数均最大,随着属或种的数量逐渐增加,其多样性明显提高,但其各项指标基本呈依次降低的趋势。通过对壳斗科植物空间多样性格局进行量化研究,获取了中国壳斗科植物空间多样性分布规律及多样性格局数量特点,利用地理信息系统技术可以使多样性研究体现出空间性和定量化的特征。     

Within-community vegetation structure in the conifer woodlands of the Siskiyou Mountains,Oregon

The conifer woodlands found on serpentine-derived soils in southwest Oregon, USA, are characterized by a debse but discontinuous shrub stratum and a species-rich herbaceous stratum. Quantitative analysis of shrub and herb distributions within 10 sites showed that small-scale patterns within the conifer woodland sites are as important as landscape-scale patterns in community organization. Gradient analysis was used to describe the distribution of herbaceous species with respect to gradients of shrub influence (shading, decreased soil temperature, increased soil moisture, increased litter depth) within sites and topographic moisture among sites. Regression analysis of the resulting species distributions and calculations of alpha and beta diversity showed that (a) the shrub-influence microgradient significantly affected distributions for 15 out of 20 major herbaceous species, and the topographic-moisture gradient influenced 13 out of the 20 species, (b) species richness was higher under intermediate conditions along both gradients, and (c) beta diversity within communities was 2.5 to 3.8 times the beta diversity of the site-to-site topographic-moisture gradient.     

Ocean-scale patterns of 'biodiversity' of Atlantic asteroids determined from taxonomic distinctness and other measures

We examine patterns of ‘gamma’ (within-rcgion) and ‘beta’ (between-region) diversity from analysis of a presence/absence dataset for species of asteroids encompassing the whole Atlantic Ocean partitioned into 26 regions. Absolute species numbers (a poor measure of biodiversity) in shallow coastal areas and the deep sea are the same, although species richness per area for two well-sampled regions suggests, qualitatively, that coastal areas may be more speciose. Taxonomic distinctness (A*), an index which is markedly less sample-size dependent than other common diversity measures, shows no significant association with geographic area and no clear pattern with depth, suggesting an absence of latitudinal and coastal/deep trends. Cluster analysis shows that distinctive faunal assemblages are most evident in shelf/ shallow waters, where six groupings separate recognizably acccording to geographical location. Three of these arc the southernmost regions of the Atlantic (southeast of S. America, S. Angola/S. Africa & Tristan da Cunha/Gough Island) and arc characterized by their isolation and high levels of endemism. As depth increases so does the amount of faunal similarity between regions. This indicates that beta diversity is highest in shelf regions and lowest in lower bathyal/abyssal regions. Our results may support the contention which questions the emerging paradigm that the deep sea has exceptionally high diversity. It is evident, however, that comparisons (e.g. between coasts and the deep sea) are problematic and can depend very much on the element(s) of biodiversity measured, sampling methods and the spatial scales (e.g. alpha, beta or gamma diversity) over which assessment is made. Any wider conclusions should therefore be drawn cautiously, particularly since assessment is made of only one faunal group. Other findings include significant correlation between the depth range of asteroids and their geographical range. The utility of low-resolution datasets is reviewed. It is concluded that within limitations they can be of value for determining broad (e.g. regional, ocean-scale and global-scale) patterns of diversity and community structure, especially when analysed using measures relatively uninfluenced by sample size.     

Geographical patterns in the beta diversity of China's woody plants: the influence of space,environment and range size

Beta diversity (i.e. species turnover rate across space) is fundamental for understanding mechanisms controlling large‐scale species richness patterns. However, the influences on beta diversity are still a matter of debate. In particular, the relative role of environmental and spatial processes (e.g. environmental niche versus dispersal limitation of species) remains elusive, and the influence of species range size has been poorly tested. Here, using distribution maps of 11 405 woody species in China (ca 9.6 × 10⁶ km²), we investigated 1) the geographical and directional patterns of beta diversity for all woody species and species with different range sizes, and 2) compared the effects of environmental and spatial processes on these patterns. Beta diversity was calculated as the decay of similarity in species composition with increasing distance. Variables representing environmental energy, water availability, climatic seasonality, habitat heterogeneity and human activities were used to evaluate the effects of environmental processes, while spatial distance was used to assess the influence of spatial processes. The results indicated significant directional patterns of beta diversity: the similarity decay along the latitudinal gradient was 1.6–2.3 times faster than that along the longitudinal gradient. Beta diversity also increased with the decrease of species range size. As compared with spatial processes, environmental processes had stronger effects on longitudinal beta diversity and on the beta diversity of widely‐ranged species. This was opposite to the larger influence of spatial processes on latitudinal beta diversity and the beta diversity of narrowly‐ranged species. These results suggest that the distributions of narrowly‐ranged woody species in China may have not reached equilibrium with their environmental niches due to dispersal limitation induced by China's topography and/or their low dispersal ability. The projected rapid climatic changes will likely endanger such species. Species dispersal processes should be taken into account in future conservation strategies in China.     

Mapping of arthropod alpha and beta diversity in heterogeneous arctic-alpine ecosystems

Assessing biodiversity in arctic-alpine ecosystems is a costly task. We test in the current study whether we can map the spatial patterns of spider alpha and beta diversity using remotely-sensed surface reflectance and topography in a heterogeneous alpine environment in Central Norway. This proof-of-concept study may provide a tool for an assessment of arthropod communities in remote study areas. Data on arthropod species distribution and richness were collected through pitfall trapping and subjected to a detrended correspondence analysis (DCA) to extract the main species composition gradients. The DCA axis scores as indicators of species composition as well as trap species richness were regressed against a combined data set of surface reflectance as measured by the Sentinel-2 satellite and topographical parameters extracted from a digital elevation model. The models were subsequently applied to the spatial data set to achieve a pixel-wise prediction of both species richness and position in the DCA space. The spatial variation in the modelled DCA scores was used to draw conclusions regarding spider beta-diversity. The species composition was described with two DCA axes that were characterized by post hoc-defined indicator species, which showed a typical annidation in the arctic-alpine environment under study. The fits of the regression models for the DCA axes and species richness ranged from R² = 0.25 up to R² = 0.62. The resulting maps show strong gradients in alpha and beta diversity across the study area. Our results indicate that the diversity patterns of spiders can at least partially be explained by means of remotely sensed data. Our approach would likely benefit from the additional use of high resolution aerial photography and LiDAR data and may help to improve conservation strategies in arctic-alpine ecosystems.     

Are there latitudinal gradients in species turnover?

Aim To examine the effect on the observed relationship between spatial turnover and latitude of both the measure of beta diversity used and the method of analysis. Location The empirical analyses presented herein are for the New World. Methods We take the spatial distributions of the owls of the New World as an exemplar data set to investigate the patterns of beta diversity across latitudes revealed by different analytical methods. To illustrate the strengths and weaknesses of alternative measures of beta diversity and different analytical approaches, we also use a simple random distribution model, focusing in particular on the influence of richness gradients and landmass geometry. Results Our simple spatial model of turnover demonstrates that different combinations of analytical approach and measure of beta diversity can give rise to strikingly different relationships between turnover and latitude. The analyses of the bird data for the owls of the New World demonstrate that this observation extends to real data. Conclusions For the particular assemblage considered, we present strong evidence that species richness declines at higher latitudes, and there is also some evidence that species turnover is greater nearer the equator, despite conceptual and practical difficulties involved in analysing spatial patterns of species turnover. We suggest some ways of overcoming these difficulties.     

Biotic homogenisation and differentiation as directional change in beta diversity: synthesising driver–response relationships to develop conceptual models across ecosystems

Biotic homogenisation is defined as decreasing dissimilarity among ecological assemblages sampled within a given spatial area over time. Biotic differentiation, in turn, is defined as increasing dissimilarity over time. Overall, changes in the spatial dissimilarities among assemblages (termed ‘beta diversity’) is an increasingly recognised feature of broader biodiversity change in the Anthropocene. Empirical evidence of biotic homogenisation and biotic differentiation remains scattered across different ecosystems. Most meta-analyses quantify the prevalence and direction of change in beta diversity, rather than attempting to identify underlying ecological drivers of such changes. By conceptualising the mechanisms that contribute to decreasing or increasing dissimilarity in the composition of ecological assemblages across space, environmental managers and conservation practitioners can make informed decisions about what interventions may be required to sustain biodiversity and can predict potential biodiversity outcomes of future disturbances. We systematically reviewed and synthesised published empirical evidence for ecological drivers of biotic homogenisation and differentiation across terrestrial, marine, and freshwater realms to derive conceptual models that explain changes in spatial beta diversity. We pursued five key themes in our review: (i) temporal environmental change; (ii) disturbance regime; (iii) connectivity alteration and species redistribution; (iv) habitat change; and (v) biotic and trophic interactions. Our first conceptual model highlights how biotic homogenisation and differentiation can occur as a function of changes in local (alpha) diversity or regional (gamma) diversity, independently of species invasions and losses due to changes in species occurrence among assemblages. Second, the direction and magnitude of change in beta diversity depends on the interaction between spatial variation (patchiness) and temporal variation (synchronicity) of disturbance events. Third, in the context of connectivity and species redistribution, divergent beta diversity outcomes occur as different species have different dispersal characteristics, and the magnitude of beta diversity change associated with species invasions also depends strongly on alpha and gamma diversity prior to species invasion. Fourth, beta diversity is positively linked with spatial environmental variability, such that biotic homogenisation and differentiation occur when environmental heterogeneity decreases or increases, respectively. Fifth, species interactions can influence beta diversity via habitat modification, disease, consumption (trophic dynamics), competition, and by altering ecosystem productivity. Our synthesis highlights the multitude of mechanisms that cause assemblages to be more or less spatially similar in composition (taxonomically, functionally, phylogenetically) through time. We consider that future studies should aim to enhance our collective understanding of ecological systems by clarifying the underlying mechanisms driving homogenisation or differentiation, rather than focusing only on reporting the prevalence and direction of change in beta diversity, per se.