The promise and pitfalls of β‐diversity in ecology and conservation

A key challenge in ecology and conservation is to determine how processes at different scales create variation in community composition (β‐diversity). In this issue, Oldén & Halme show that grazers increase β‐diversity through multiple processes at different scales. We discuss how β‐diversity can elucidate fundamental processes of community assembly, challenges in linking processes to patterns, and unresolved questions across scales.     

Deterministic diversity changes in freshwater phytoplankton in the Yunnan–Guizhou Plateau lakes in China

Diversity measures reflect different aspects of a community, which are determined by different ecological processes. However, information is still limited on the ecological processes that are represented by different measures of species diversity. In this study, the primary driving factors for richness and diversity indices were tested. The possible ecological processes represented by each index were analyzed. First, the type of ecological process that governed the phytoplankton community in the Yunnan–Guizhou Plateau lakes, either deterministic or stochastic, was identified by Caswell's neutral model. The results indicate that a deterministic process governs the phytoplankton community. Second, the driving factors of richness and diversity indices were screened with mixed models. The results suggest that the variation of phytoplankton richness in different lakes or sites was primarily related to bottom-up factors. The variations in evenness and other measures based on the relative abundance were driven by both top-down and bottom-up factors, such as zooplankton biomass, and pH and mean light, respectively. Finally, although the different measures of diversity may respond to specific bottom-up or top-down processes, the responses to the two processes were not independent of each other. These findings will increase our understanding of the relationships between ecological processes and diversity measures for freshwater phytoplankton.     

Ignoring spatial effects results in inadequate models for variation in littoral macroinvertebrate diversity

Studies focusing on the effects of spatial processes versus environmental filtering on aquatic metacommunities have so far been focused almost entirely on relatively isolated systems, such as sets of different lakes or streams. In contrast, metacommunity patterns and underlying processes within a single aquatic system have received less attention. In this study, we aimed to examine how strongly variations in different diversity indices are affected by spatial processes (dispersal) versus local environmental conditions (species sorting) within a large lake system. Modern biodiversity research focuses on multiple diversity facets because different indices may be uncorrelated within and between facets, and they may thus describe different phenomena. We investigated the relationship of littoral macroinvertebrate diversity with environmental and spatial factors using 10 indices of species, functional and taxonomic diversity. Using spatial factors as proxies of dispersal, we decomposed variation in diversity indices into fractions attributable to environmental and spatial factors. Our results highlighted generally equal or higher importance of spatial processes in controlling the variation in diversity indices when compared to local environmental variables. Local environmental conditions accounted for higher proportion of variation only in a single index (i.e. taxonomic diversity). These findings suggest that the effects of high dispersal rates (mass effects) may override the influences of local environmental conditions (species sorting) on the diversity in highly‐connected aquatic system, such as large lakes and marine coastal systems. Our results further suggest that biodiversity assessment and environmental monitoring in highly‐connected systems cannot rely solely on the idea of environmental control. We hence recommend that the roles of both environmental and spatial processes should be integrated in basic and applied ecological research of aquatic systems.     

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.     

生态学的多样性指数:功能与系统发育

生物多样性是生态学的核心问题。传统的多样性指数仅包含物种数和相对多度的信息,这类基于分类学的多样性指数并不能很好地帮助理解群落构建和生态系统功能。不同物种对群落构建和生态系统功能所起到的作用类型和贡献也不完全相同,且物种在生态过程中的作用和贡献往往与性状密切相关,因此功能多样性已经成为反映物种群落构建、干扰以及环境因素对群落影响的重要指标。同时,由于亲缘关系相近的物种往往具有相似的性状,系统发育多样性也可以作为功能多样性的一个替代。功能多样性和系统发育多样性各自具有优缺点,但二者均比分类多样性更能揭示群落和生态系统的构建、维持与功能。     

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.     

Genetic variation of loci potentially under selection confounds species–genetic diversity correlations in a fragmented habitat

Positive species–genetic diversity correlations (SGDCs) are often thought to result from the parallel influence of neutral processes on genetic and species diversity. Yet, confounding effects of non‐neutral mechanisms have not been explored. Here, we investigate the impact of non‐neutral genetic diversity on SGDCs in high Andean wetlands. We compare correlations between plant species diversity and genetic diversity (GD) calculated with and without loci potentially under selection (outlier loci). The study system includes 2188 specimens from five species (three common aquatic macroinvertebrate and two dominant plant species) that were genotyped for 396 amplified fragment length polymorphism loci. We also appraise the importance of neutral processes on SGDCs by investigating the influence of habitat fragmentation features. Significant positive SGDCs were detected for all five species (mean SGDC = 0.52 ± 0.05). While only a few outlier loci were detected in each species, they resulted in significant decreases in GD and in SGDCs. This supports the hypothesis that neutral processes drive species–genetic diversity relationships in high Andean wetlands. Unexpectedly, the effects on genetic diversity GD of the habitat fragmentation characteristics in this study increased with the presence of outlier loci in two species. Overall, our results reveal pitfalls in using habitat features to infer processes driving SGDCs and show that a few loci potentially under selection are enough to cause a significant downward bias in SGDC. Investigating confounding effects of outlier loci thus represents a useful approach to evidence the contribution of neutral processes on species–genetic diversity relationships.     

Phylogenetic beta diversity: linking ecological and evolutionary processes across space in time

A key challenge in ecological research is to integrate data from different scales to evaluate the ecological and evolutionary mechanisms that influence current patterns of biological diversity. We build on recent attempts to incorporate phylogenetic information into traditional diversity analyses and on existing research on beta diversity and phylogenetic community ecology. Phylogenetic beta diversity (phylobetadiversity) measures the phylogenetic distance among communities and as such allows us to connect local processes, such as biotic interactions and environmental filtering, with more regional processes including trait evolution and speciation. When combined with traditional measures of beta diversity, environmental gradient analyses or ecological niche modelling, phylobetadiversity can provide significant and novel insights into the mechanisms underlying current patterns of biological diversity.     

Phylogenetic and compositional diversity are governed by different rules: a study of fleas parasitic on small mammals in four biogeographic realms

We studied patterns of phylogenetic and compositional diversity of fleas parasitic on small mammals and asked whether these patterns are affected by environmental variation or evolutionary/historical processes. We considered environmental variation via both off‐host (air temperature, precipitation, the amount of green vegetation, latitude) and host‐associated (phylogenetic and species composition) environments. The indicators of evolutionary/historical processes were phylogenetic and compositional uniqueness estimated via phylogenetic or compositional, respectively, β‐diversity of either fleas or hosts. We found that phylogenetic uniqueness of flea assemblages was the main predictor of their phylogenetic diversity in all realms. In addition, host phylogenetic diversity and uniqueness played also some role in the Palearctic, whereas the effect of the off‐host environment was either extremely weak or absent. Compositional diversity of fleas was consistently affected by compositional diversity of hosts in all realms except the Neotropics. The effect of the off‐host environment on compositional flea diversity was substantial in all realms except the Palearctic. No effect of latitude on either metric of flea diversity was found. We conclude that phylogenetic diversity of fleas is driven mainly by evolutionary/historical processes, whereas drivers of their compositional diversity are associated with current ecological conditions.     

Hydrological stability drives both local and regional diversity patterns in rock pool metacommunities

A main challenge associated with macro ecological gradients such as the latitudinal diversity gradient (LDG) is that proxies of potential underlying processes are often correlated at large scales. One way to reliably identify contributing processes is to show that they can lead to similar responses at local scales. Using a set of invertebrate communities from rock pool clusters along a latitudinal gradient in Australia, we investigated the importance of hydrological stability for explaining both local and regional diversity patterns in this habitat. Results show that, at both local and regional scales, habitat stability in terms of the frequency and length of inundations was strongly correlated to local alpha diversity in individual pools and to gamma diversity at the level of pool clusters. Additionally, partitioning beta diversity into components of nestedness and species turnover revealed that communities in unstable habitats were nested subsets of communities in more stable habitats. Overall, this study provides convincing mechanistic support for the climate stability hypothesis as a potential explanation for the LDG in this system. Results also indicate that when there is enough time for dispersal and colonization, regional processes can be relatively unimportant compared to local processes to explain large scale diversity patterns.     

Drivers of the beta diversity of spider assemblages in southern Brazilian temporary wetlands

1. The composition of local assemblages is assembled by an interplay of species sorting, mass effects and dispersal limitation processes. The contributions of assembly processes to metacommunity structure can change with ecosystem type and specificities of the study area. Spider composition is influenced by environmental features such as habitat structure and climate, and also by spatial distances between patches. However, little is known about the roles of assembly processes in spider metacommunity structure in wetlands. 2. The beta diversity patterns of spider assemblages were assessed in 24 temporary wetlands distributed along a latitudinal gradient in southern Brazil. The study also assessed the individual correspondence of beta diversity (and its turnover and richness components) with dissimilarities in habitat structure and climate, as well as with geographic distances, using Mantel and partial Mantel correlation tests and multivariate correlograms. 3. Turnover was the most important component of spider beta diversity. Mantel tests detected significant correlations of spider beta diversity with habitat structure. Partial Mantel tests detected significant relationships only between spider beta diversity (and the richness component) and geographic distances. Additionally, spider composition was more similar than chance on smaller scales. 4. These results evidenced a complex interplay of assembly processes explaining spider metacommunity structure in temporary wetlands. Although species-sorting processes associated with habitat structure were important in structuring local spider composition, mass effects and dispersal limitation across climatic zones played an important role on a broader scale.     

Dispersal and diversity in experimental metacommunities: linking theory and practice

There has been a recent rise in the number of experiments investigating the effect of dispersal on diversity, with many of the predictions for these tests derived from metacommunity theory. Despite the promise of linking observed relationships between dispersal and diversity to underlying metacommunity processes, empirical studies have faced challenges in providing robust tests of theory. We review experimental studies that have tested how dispersal affects metacommunity diversity to determine why shortcomings emerge, and to provide a framework for empirical tests of theory that capture the processes structuring diversity in natural metacommunities. We first summarize recent experimental work to outline trends in results and to highlight common methods that cause a misalignment between empirical studies and the processes described by theory. We then identify the undesired implications of three widely used experimental methods that homogenize metacommunity structure or species traits, and present alternative methods that have been used to successfully integrate experiments and theory in a biologically relevant way. Finally, we present methodological and theoretical insights from three related ecological fields (coexistence, food web and priority effects theory) that, if integrated into metacommunity experiments, could help isolate the independent and joint effects of local interactions and dispersal on diversity, and reveal the mechanisms underlying observed dispersal–diversity patterns. Together, these methods can provide stronger tests of existing theory and stimulate new theoretical explorations. Synthesis Although metacommunity experiments offer a unique opportunity to test classic and emerging theory on the relationship between dispersal and diversity, several common challenges have hindered robust tests of theory. We outline how emerging theory on the invasion criterion, food webs and priority effects could be help clarify when and how dispersal affects metacommunity diversity, and identify when experimental approaches that homogenize metacommunities fail to test existing theory. By forging better links between theoretical and empirical work, we hope to motivate novel and improved experimental approaches to understanding the joint effects of local and regional processes on diversity.     

The Functional Gene Diversity in Natural Populations over Postglacial Areas: The Shaping Mechanisms Behind Genetic Composition of Longnose Dace (Rhinichthys cataractae) in Northeastern North America

The diversity of functional genes and the related processes are important issues for conservation biology. This is especially relevant for populations that have suffered from demographic reduction as a consequence of the processes of postglacial colonization. In this perspective, the aims of the present study are (1) to quantify the genetic diversity of functional genes and (2) to disentangle the long- and short-term effects of natural selection that shapes genetic diversity from those of drift, mutation, and allopatric fragmentation. This research was conducted using an extensive genetic polymorphism analysis of populations of longnose dace (Rhinichthys cataractae) living over an area once covered by Pleistocene glaciations. The sequence and diversity of one exon of three genes (MHC IIβ, growth hormone, and trypsin) were jointly analyzed with non-coding nuclear loci from 27 populations; these populations were sampled over four major basins of northeastern North America. The survey revealed a surprisingly low allelic richness, especially for the MHC gene, considering the number of individuals and populations sampled. The results suggest that there is a complex mixture of different evolutionary processes shaping the level of polymorphism among longnose dace. While our study underlines the importance of the short-term effects of neutral processes and the major impact of post-glacial colonization on gene diversity, locally dependent balancing selection was detected on MHC. From this perspective, our results support an understanding of the importance of drift on functional gene diversity but also highlight the transient effects of natural selection on allelic composition, even in populations that show drastic reduction of genetic diversity.     

植物功能多样性与功能群研究进展

综述了植物功能多样性与功能群研究的最新进展。介绍了植物功能群的定义及植物功能群的划分方法。在功能多样性与生态系统资源动态关系方面．抽样效应和生态位互补效应用来解释植物多样性在生态系统资源动态中的作用。功能多样性与生态系统的稳定性间的关系可以用生态冗余或生态保险概念来解释,这两个概念是一个问题的两个侧面,是多样性与生态系统功能争论的焦点。     

Assessing the ecological significance of molecular diversity data in natural plant populations

Despite extensive research for several decades, there remains a lack of understanding of the processes that determine the dynamics of natural plant communities. In this paper some current concepts in vegetation dynamics are reviewed and an attempt is made to provide a perspective of the way in which data for molecular diversity might be used to help in developing an understanding of population processes. It is proposed that data from assessments of general population diversity, and specific ecophysiological traits can be used to assess the potential for individual species to compete and substitute for each other in a community.Keywords: Natural plant communities, dynamics, molecular diversity, population diversity, ecophysiological traits.      

Loss in microbial diversity affects nitrogen cycling in soil

Microbial communities have a central role in ecosystem processes by driving the Earth''s biogeochemical cycles. However, the importance of microbial diversity for ecosystem functioning is still debated. Here, we experimentally manipulated the soil microbial community using a dilution approach to analyze the functional consequences of diversity loss. A trait-centered approach was embraced using the denitrifiers as model guild due to their role in nitrogen cycling, a major ecosystem service. How various diversity metrics related to richness, eveness and phylogenetic diversity of the soil denitrifier community were affected by the removal experiment was assessed by 454 sequencing. As expected, the diversity metrics indicated a decrease in diversity in the 1/10³ and 1/10⁵ dilution treatments compared with the undiluted one. However, the extent of dilution and the corresponding reduction in diversity were not commensurate, as a dilution of five orders of magnitude resulted in a 75% decrease in estimated richness. This reduction in denitrifier diversity resulted in a significantly lower potential denitrification activity in soil of up to 4–5 folds. Addition of wheat residues significantly increased differences in potential denitrification between diversity levels, indicating that the resource level can influence the shape of the microbial diversity–functioning relationship. This study shows that microbial diversity loss can alter terrestrial ecosystem processes, which suggests that the importance of functional redundancy in soil microbial communities has been overstated.     

Reconciling the contribution of environmental and stochastic structuring of tropical forest diversity through the lens of imaging spectroscopy

Both niche and stochastic dispersal processes structure the extraordinary diversity of tropical plants, but determining their relative contributions has proven challenging. We address this question using airborne imaging spectroscopy to estimate canopy β‐diversity for an extensive region of a Bornean rainforest and challenge these data with models incorporating niches and dispersal. We show that remotely sensed and field‐derived estimates of pairwise dissimilarity in community composition are closely matched, proving the applicability of imaging spectroscopy to provide β‐diversity data for entire landscapes of over 1000 ha containing contrasting forest types. Our model reproduces the empirical data well and shows that the ecological processes maintaining tropical forest diversity are scale dependent. Patterns of β‐diversity are shaped by stochastic dispersal processes acting locally whilst environmental processes act over a wider range of scales.     

Plant diversity and root traits benefit physical properties key to soil function in grasslands

Plant diversity loss impairs ecosystem functioning, including important effects on soil. Most studies that have explored plant diversity effects belowground, however, have largely focused on biological processes. As such, our understanding of how plant diversity impacts the soil physical environment remains limited, despite the fundamental role soil physical structure plays in ensuring soil function and ecosystem service provision. Here, in both a glasshouse and a long‐term field study, we show that high plant diversity in grassland systems increases soil aggregate stability, a vital structural property of soil, and that root traits play a major role in determining diversity effects. We also reveal that the presence of particular plant species within mixed communities affects an even wider range of soil physical processes, including hydrology and soil strength regimes. Our results indicate that alongside well‐documented effects on ecosystem functioning, plant diversity and root traits also benefit essential soil physical properties.     

Examining residual spatial correlation in variation partitioning of beta diversity in a subtropical forest

Aims The relative roles of ecological processes in structuring beta diversity are usually quantified by variation partitioning of beta diversity with respect to environmental and spatial variables or gamma diversity. However, if important environmental or spatial factors are omitted, or a scale mismatch occurs in the analysis, unaccounted spatial correlation will appear in the residual errors and lead to residual spatial correlation and problematic inferences.     

全球变化对土壤动物多样性的影

陆地生态系统由地上和地下两部分组成,二者相互作用共同影响生态系统过程和功能.土壤动物在生物地球化学循环方面起着重要作用.随着人们对土壤动物在生态系统过程中重要性的认识,越来越多的研究表明全球变化对土壤动物多样性产生深刻影响.土地利用方式的改变、温度增加和降雨格局的改变能直接影响土壤动物多样性.CO₂浓度和氮沉降的增加主要通过影响植物群落结构、组成和化学成分对土壤动物多样性产生间接影响.不同环境因子之间又能相互作用共同影响土壤动物多样性.了解全球变化背景下不同驱动因子及其交互作用对土壤动物多样性的影响,有助于更好地预测未来土壤动物多样性及相关生态学过程的变化.