Examining differences in phylogenetic composition enhances understanding of the phylogenetic structure of the shrub community in the northeastern Qinghai‐Tibetan Plateau

Periodic climatic oscillations and species dispersal during the postglacial period are two important causes of plant assemblage and distribution on the Qinghai‐Tibet Plateau (QTP). To improve our understanding of the bio‐geological histories of shrub communities on the QTP, we tested two hypotheses. First, the intensity of climatic oscillations played a filtering role during community structuring. Second, species dispersal during the postglacial period contributed to the recovery of species and phylogenetic diversity and the emergence of phylogenetic overdispersion. To test these hypotheses, we investigated and compared the shrub communities in the alpine and desert habitats of the northeastern QTP. Notably, we observed higher levels of species and phylogenetic diversity in the alpine habitat than in the desert habitat, leading to phylogenetic overdispersion in the alpine shrub communities versus phylogenetic clustering in the desert shrub communities. This phylogenetic overdispersion increased with greater climate anomalies. These results suggest that (a) although climate anomalies strongly affect shrub communities, these phenomena do not act as a filter for shrub community structuring, and (b) species dispersal increases phylogenetic diversity and overdispersion in a community. Moreover, our investigation of the phylogenetic community composition revealed a larger number of plant clades in the alpine shrub communities than in the desert shrub communities, which provided insights into plant clade‐level differences in the phylogenetic structures of alpine and desert shrub communities in the northeastern QTP.     

Exploring the community phylogenetic structure along the slope aspect of subalpine meadows in the eastern Qinghai–Tibetan Plateau,China

Exploring the community assembly has been important for explaining the maintenance mechanisms of biodiversity and species coexistence, in that it is a central issue in community ecology. Here, we examined patterns of the community phylogenetic structure of the subalpine meadow plant community along the slope gradient in the Qinghai–Tibetan Plateau of China. We surveyed all species and constructed the phylogenetic tree of the plant community based on data from the Angiosperm Phylogeny Group III. We selected the net relative index (NRI) and evaluated the community phylogenetic structure along the five slope plants communities. We found that the phylogenetic structure varied from phylogenetic clustering to phylogenetic overdispersion with the slope aspect from north to south. In the north slope, the community phylogenetically cluster indicated that the limiting similarity played a leading role in the community assembly and the maintenance of biodiversity. Community phylogenetic overdispersion in the east, southeast, and south slopes indicated that habitat filtration was the driving force for community assembly. The NRI index of the northeast slope was close to zero, implying random dispersion. But it may be driven by the neutral process or limiting similarity, in that the community assembly process was the result of a combination of several ecological factors and thus required further study.     

太行山北段地区荆条灌丛和三裂绣线菊灌丛群落谱系结构

灌丛是太行山地区最重要的生态系统类型之一, 灌丛群落生物多样性的维持及其生态系统服务功能对京津冀地区的生态安全具有重要作用。本研究选择太行山最具代表性的两种灌木群落——荆条(Vitex negundo var. heterophylla)灌丛和三裂绣线菊(Spiraea trilobata)灌丛为研究对象, 利用净亲缘关系指数(net relatedness index, NRI)和多元回归等方法探究了两种灌丛群落构建机制的异同及主要的环境影响因子, 同时还利用谱系结构主坐标分析(principal coordinates of phylogenetic structure, PCPS)对决定群落谱系结构的关键系统发育节点进行了探究。结果表明: 两种灌丛群落内灌木植物的物种多样性没有显著差异, 但谱系结构差异显著。三裂绣线菊群落表现出显著的谱系发散趋势, 而荆条群落谱系聚集程度高于三裂绣线菊群落, 但未表现出显著的谱系结构。三裂绣线菊灌丛群落构建的驱动机制是生态位分化, 荆条灌丛中生境过滤作用有所增加, 与生态位分化共同驱动其群落构建过程。与干旱胁迫相关的生境过滤因素增加是荆条灌丛群落谱系聚集程度增加的重要原因。PCPS二维排序结果表明: 荆条灌丛群落谱系趋向聚集与其群落内缺乏蔷薇目、壳斗目等亲缘关系较远的类群有关, 而三裂绣线菊灌丛群落内物种则包含较多的演化分支。总体而言, 环境过滤不是决定太行山地区灌丛群落构建的主要驱动因素, 但水分条件仍然是影响区域群落谱系结构的重要因素。     

阿拉善荒漠灌丛群落谱系结构及其影响因子

为探究阿拉善荒漠灌丛群落的构建机制,该研究选取净亲缘关系指数(NRI)作为谱系结构指数,在对阿拉善荒漠灌丛群落野外调查的基础上,以群落物种组成为基础数据,计算各样地群落的NRI,并分析NRI在经纬度梯度上的变化趋势及其与土壤因子和水热因子的关系。结果表明:(1)阿拉善荒漠灌丛群落谱系结构在阿拉善高原东南部以发散状态为主,在阿拉善高原西部和北部地区以聚集状态为主。(2)阿拉善荒漠灌丛群落的NRI随经度的升高而减小,随纬度的升高而增大。(3)阿拉善荒漠土壤质地、土壤容重、土壤pH值和土壤有机碳含量与其群落谱系结构均无显著相关性;在降水因子和温度因子中,与群落谱系结构相关系数最大的分别为年降水量和年温度变化范围(最暖月最高温与最冷月最低温的差值),其中:年降水量与NRI呈显著负相关关系,年温度变化范围与NRI呈显著正相关关系,且最暖月最高温和最冷月最低温与NRI均有显著相关性,推测年温度变化范围对阿拉善灌丛群落谱系结构的影响是通过最暖月最高温和最冷月最低温起作用的。研究发现,阿拉善高原东南部区域的荒漠灌丛群落构成主要受竞争排斥的作用,其西部和北部地区的群落构成主要受环境过滤的影响;阿拉善荒漠灌丛群落的谱系结构主要受年降水量和极端温度的影响。     

Comparative analyses of leaf anatomy of dicotyledonous species in Tibetan and Inner Mongolian grasslands

Knowledge of the leaf anatomy of grassland plants is crucial for understanding how these plants adapt to the environment. Tibetan alpine grasslands and Inner Mongolian temperate grasslands are two major grassland types in northern China. Tibetan alpine grasslands occur in high-altitude regions where the low temperatures limit plant growth. Inner Mongolian temperate grasslands are found in arid regions where moisture is the limiting factor. Few comparative studies concerning the leaf anatomy of grassland plants of the Tibetan Plateau and Inner Mongolian Plateau have been conducted. We examined leaf characteristics at 71 sites and among 65 species, across the alpine grasslands of the Tibetan Plateau and the temperate grasslands of the Inner Mongolian Plateau. We compared the leaf structures of plants with different life forms and taxonomies, and their adaptation to arid or cold environments. We explored relationships among leaf features and the effects of climatic factors (i.e., growing season temperature and precipitation) on leaf characteristics. Our results showed that (i) there were significant differences in leaf anatomy between Tibetan alpine and Inner Mongolian temperate grasslands. Except for mesophyll cell density, the values obtained for thickness of leaf tissue, surface area and volume of mesophyll cells were larger on the Tibetan Plateau than on the Inner Mongolian Plateau. (ii) Within the same family or genus, leaf anatomy showed significant differences between two regions, and trends were consistent with those of whole species. (iii) Leaf anatomy of woody and herbaceous plants also showed significant differences between the regions. Except for mesophyll cell density, the values obtained for the thickness of leaf tissue, and the surface area and volume of mesophyll cells were larger in herbaceous than in woody plants. (iv) Leaf anatomical traits changed accordingly. Total leaf thickness, thicknesses of lower and upper epidermal cells, and surface area and volume of mesophyll cells were positively correlated, while mesophyll cell density was negatively associated with those traits. (v) Growing season temperature had stronger effects on leaf anatomy than growing season precipitation. Although the communities in Tibetan and Inner Mongolian grasslands were similar in appearance, leaf anatomy differed; this was probably due to the combined effects of evolutionary adaptation of plants to environment and environmental stress induced by climatic factors.     

Bird species richness is associated with phylogenetic relatedness,plant species richness,and altitudinal range in Inner Mongolia

Bird species richness is mediated by local, regional, and historical factors, for example, competition, environmental heterogeneity, contemporary, and historical climate. Here, we related bird species richness with phylogenetic relatedness of bird assemblages, plant species richness, topography, contemporary climate, and glacial‐interglacial climate change to investigate the relative importance of these factors. This study was conducted in Inner Mongolia, an arid and semiarid region with diverse vegetation types and strong species richness gradients. The following associated variables were included as follows: phylogenetic relatedness of bird assemblages (Net Relatedness Index, NRI), plant species richness, altitudinal range, contemporary climate (mean annual temperature and precipitation, MAT and MAP), and contemporary‐Last Glacial Maximum (LGM) change in climate (change in MAT and change in MAP). Ordinary least squares linear, simultaneous autoregressive linear, and Random Forest models were used to assess the associations between these variables and bird species richness across this region. We found that bird species richness was correlated negatively with NRI and positively with plant species richness and altitudinal range, with no significant correlations with contemporary climate and glacial–interglacial climate change. The six best combinations of variables ranked by Random Forest models consistently included NRI, plant species richness, and contemporary‐LGM change in MAT. Our results suggest important roles of local ecological factors in shaping the distribution of bird species richness across this semiarid region. Our findings highlight the potential importance of these local ecological factors, for example, environmental heterogeneity, habitat filtering, and biotic interactions, in biodiversity maintenance.     

Interactions,Environmental Sorting and Chance: Phylostructure of a Tropical Forest Assembly

Density dependence, environmental sorting and chance have been discussed for the purpose of understanding, predicting and explaining the species richness, composition and structural parameters of living communities. Different ecological mechanisms occur individually in an overlapping manner, so the structure of each local community is influenced by an independent mixture of these factors. To identify which of these factors prevails in organizing the species-rich tree community from 100 plots of 10 × 10 m in a primary forest patch (the Forest of Seu Nico – FSN, from the Atlantic Forest domain), we analyzed species-environment correlations via canonical correspondence analysis and identified two different pedo-environments. We analyzed the community’s phylogenetic structure using Phylocom 4.2 software to calculate the net relatedness index (NRI) and the nearest taxon index (NTI). Furthermore, we partitioned the total phylogenetic diversity into independent α and β components (Π_ST). To reveal the overlap of ecological mechanisms such as neutrality, environmental filtering and density-dependent factors, we analyzed the phylogenetic structure in both pedo-environments. The species-environment correlations observed in the FSN are weak in comparison with those found in other studies, although the permanent plot presents a short environmental gradient, dividing the plot into an upper, more acidic hillside and a lower, more fertile bottom. The overall phylogenetic structure of the FSN community shows strong and significant phylogenetic overdispersion. This overdispersion indicates that density-dependent factors, such as interspecific competition, play an important role in maintaining the species richness and community structure in megadiverse ecosystems such as the FSN when we assume traits to be conserved within evolutionary lineages. The NRI and NTI are correlated positively with the soil pH and negatively with the soil’s aluminum concentration, so the bottom plots show higher phylogenetic overdispersion and lower Π_ST values than the hillside plots. This pattern can be explained by the greater importance of environmental filters in more acidic soils that form less favorable habitats, while the influence of competition and therefore also the rate of competitive exclusion are higher in the more favorable, less acidic plots.     

柴达木盆地荒漠灌丛群落谱系结构研究

谱系信息是群落生态学和保育生物学研究的主要内容之一。为探究柴达木盆地荒漠灌丛群落谱系结构及其与环境因子的关系,该研究以柴达木盆地荒漠灌丛为对象,基于群落中物种存在与否的物种组成数据,使用R语言中picante软件包计算了灌丛群落谱系多样性指数和谱系结构指数,并且分析了谱系结构指数与年均温度、年均降水以及土壤含水量之间的关系,以揭示柴达木盆地灌丛群落物种之间的亲缘关系和群落生物多样性维持机制。结果表明:(1)柴达木盆地灌丛群落谱系结构与土壤含水量之间存在极显著相关性(P=2.77×10-6),随着土壤含水量的增加,群落谱系结构聚集程度逐渐降低,表现出生境过滤作用逐步减弱,生物间相互作用逐渐加强的变化趋势。(2)群落谱系结构与年均温度、年均降水之间无显著相关性。(3)典型荒漠生境灌丛和河谷(河漫滩)生境灌丛群落的谱系结构差异显著(P0.05),整体上分别表现为谱系聚集状态和谱系发散状态;河谷(河漫滩)生境灌丛群落的谱系多样性显著高于典型荒漠生境灌丛(P0.05)。(4)将群落谱系信息应用在生物多样性保护实践中,发现河谷(河漫滩)生境灌丛群落较典型荒漠生境的灌丛群落可能具有更高的保护价值。研究认为,将群落谱系研究与保育生物学理论结合将会使生物多样性保护策略更加科学有效。     

Phylogenetic clustering and overdispersion for alpine plants along elevational gradient in the Hengduan Mountains Region,southwest China

To better understand the elevational pattern of phylogenetic structure shown by alpine taxa and the underlying causes, we analyzed the phylogenetic structure of each elevational belt of alpine plants in the Hengduan Mountains Region, measured by net related index (NRI) and net nearest taxon index (NTI). We found both the indices of phylogenetic diversity indicated that alpine plants tended to show phylogenetic overdispersion at low elevational belts, implying that the distribution of alpine plants in these belts was mainly determined by interspecific competition. Alpine plants at higher elevational belts tended to phylogenetic clustering indicated by NRI, and NTIrevealed phylogenetic clustering at the belts between 4300 m and 5500 m, which presumably suggested environment filtering and rapid speciation. Above 5500 m,NTI indicated that the phylogenetic structure became random again, perhaps due to the low intensity of filtering and the large distances between plants at the top of the scree slopes. We concluded that phylogenetic structure was, indeed, influenced by the environmental filter, interspecies interaction, rapid speciation during the uplift of the Qinghai–Tibet Plateau, and distance between plants.     

Phylogenetic composition and structure of tree communities shed light on historical processes influencing tropical rainforest diversity

The Neotropics, Afrotropics and Madagascar have different histories which have influenced their respective patterns of diversity. Based on current knowledge of these histories, we developed the following predictions about the phylogenetic structure and composition of rainforest tree communities: (Hypothesis 1) isolation of Gondwanan biotas generated differences in phylogenetic composition among biogeographical regions; (H2) major Cenozoic extinction events led to lack of phylogenetic structure in Afrotropical and Malagasy communities; (H3) greater angiosperm diversification in the Neotropics led to greater phylogenetic clustering there than elsewhere; (H4) phylogenetic overdispersion is expected near the Andes due to the co‐occurrence of magnoliids tracking conserved habitat preferences and recently diversified eudicot lineages. Using abundance data of tropical rainforest tree species from 94 communities in the Neotropics, Afrotropics and Madagascar, we computed net relatedness index (NRI) to assess local phylogenetic structure, i.e. phylogenetic clustering vs. overdispersion relative to regional species pools, and principal coordinates of phylogenetic structure (PCPS) to assess variation in phylogenetic composition across communities. We observed significant differences in phylogenetic composition among biogeographical regions (agreement with H1). Overall phylogenetic structure did not differ among biogeographical regions, but results indicated variation from Andes to Amazon. We found widespread phylogenetic randomness in most Afrotropical and all Malagasy communities (agreement with H2). Most of central Amazonian communities were phylogenetically random, although some communities presented phylogenetic clustering (partial agreement with H3). We observed phylogenetic overdispersion near the Andes (agreement with H4). We were able to identify how differences in lineage composition are related to local phylogenetic co‐occurrences across biogeographical regions that have been undergoing different climatic and orographic histories during the past 100 Myr. We observed imprints of the history following Gondwana breakup on phylobetadiversity and local phylogenetic structure of rainforest tree communities in the Neotropics, Afrotropics and Madagascar.     

The phylogenetic structure of primate communities: variation within and across continents

Aim Our goals are: (1) to examine the relative degree of phylogenetic overdispersion or clustering of species in communities relative to the entire species pool, (2) to test for across‐continent differences in community phylogenetic structure, and (3) to examine the relationship between species richness and community phylogenetic structure. Location Africa, Madagascar, Asia, and the Neotropics. Methods We collected species composition and phylogenetic data for over 100 primate communities. For each community, we calculated two measures of phylogenetic structure: (1) the net relatedness index (NRI), which provides a measure of the mean pairwise phylogenetic distance among all species in the community; and (2) the nearest taxon index (NTI), which measures the relative phylogenetic distance among the closest related species in a community. Both measures are relative to the phylogeny of the species in the entire species pool. The phylocom package uses a randomization procedure to test whether the NRI and NTI values are higher or lower than expected by chance alone. In addition, we used a Kruskal–Wallis test to examine differences in NRI and NTI across continents, and linear regressions to examine the relationship between species richness and NRI/NTI. Results We found that the majority of individual primate communities in Africa, Asia and the Neotropics consist of member species that are neither more nor less closely related than expected by chance alone. Yet 37% of Malagasy communities contain species that are more distantly related to each other compared with random species assemblages. Also, we found that the average degree of relatedness among species in communities differed significantly across continents, with African and Malagasy communities consisting of more distantly related taxa compared with communities in Asia and the Neotropics. Finally, we found a significant negative relationship between species richness and phylogenetic distance among species in African, Asian and Malagasy communities. The average relatedness among species in communities decreased as community size increased. Main conclusions The majority of individual primate communities exhibit a phylogenetic structure no different from random. Yet there are across‐continent differences in the phylogenetic structure of primate communities that probably result from the unique ecological and evolutionary characteristics exhibited by the endemic species found on each continent. In particular, the recent extinctions of numerous primates on Madagascar are likely responsible for the low levels of evolutionary relatedness among species in Malagasy communities.     

Phylogenetic plant community structure along elevation is lineage specific

The trend of closely related taxa to retain similar environmental preferences mediated by inherited traits suggests that several patterns observed at the community scale originate from longer evolutionary processes. While the effects of phylogenetic relatedness have been previously studied within a single genus or family, lineage‐specific effects on the ecological processes governing community assembly have rarely been studied for entire communities or flora. Here, we measured how community phylogenetic structure varies across a wide elevation gradient for plant lineages represented by 35 families, using a co‐occurrence index and net relatedness index (NRI). We propose a framework that analyses each lineage separately and reveals the trend of ecological assembly at tree nodes. We found prevailing phylogenetic clustering for more ancient nodes and overdispersion in more recent tree nodes. Closely related species may thus rapidly evolve new environmental tolerances to radiate into distinct communities, while older lineages likely retain inherent environmental tolerances to occupy communities in similar environments, either through efficient dispersal mechanisms or the exclusion of older lineages with more divergent environmental tolerances. Our study illustrates the importance of disentangling the patterns of community assembly among lineages to better interpret the ecological role of traits. It also sheds light on studies reporting absence of phylogenetic signal, and opens new perspectives on the analysis of niche and trait conservatism across lineages.     

Phylogenies and traits provide distinct insights about the historical and contemporary assembly of aquatic insect communities

The assumption that traits and phylogenies can be used as proxies of species niche has faced criticisms. Evidence suggested that phylogenic relatedness is a weak proxy of trait similarity. Moreover, different processes can select different traits, giving opposing signals in null model analyses. To circumvent these criticisms, we separated traits of stream insects based on the concept of α and β niches, which should give clues about assembling pressures expected to act independently of each other. We investigated the congruence between the phylogenetic structure and trait structure of communities using all available traits and all possible combinations of traits (4095 combinations). To account for hierarchical assembling processes, we analyzed patterns on two spatial scales with three pools of genera. Beta niche traits selected a priori – i.e., traits related to environmental variation (e.g., respiration type) – were consistently clustered on the smaller scale, suggesting environmental filtering, while α niche traits – i.e., traits related to resource use (e.g., trophic position) – did not display the expected overdispersion, suggesting a weak role of competition. Using all traits together provided random patterns and the analysis of all possible combinations of traits provided scenarios ranging from strong clustering to overdispersion. Communities were phylogenetically overdispersed, a pattern previously interpreted as phylogenetic limiting similarity. However, our results likely reflect the co‐occurrence of ancient clades due to the stability of stream habitats along the evolutionary scale. We advise ecologists to avoid using combinations of all available traits but rather carefully traits based on the objective under consideration. Both trait and phylogenetic approaches should be kept in the ecologist toolbox, but phylogenetic distances should not be used as proxies of traits differences. Although the phylogenetic structure revealed processes operating at the evolutionary scale, only specific traits explained local processes operating in our communities.     

Linkages between woody plant proliferation dynamics and plant physiological traits in southwestern North America

Aims Woody plant encroachments in arid and semiarid ecosystems are widely reported but the physiological mechanisms still need to be further revealed. In the current study, we aim to determine whether differences in leaf physiological traits help explain grassland susceptibility to woody plant encroachment and whether distinctive physiological adaptations allow some shrub species to invade grasslands.Methods We compared physiological traits (photosynthesis, leaf water status, pigment compositions and leaf antioxidant capacities) of six species representing three functional groups: woody encroachers (Prosopis velutina, Larrea tridentata), woody non-encroachers (Acacia greggii, Lycium fremontii) and C4 grasses (Bouteloua curtipendula, Bouteloua barbata) which are naturally growing in a botanical garden in University of Arizona, USA.Important findings We infer that P. velutina (encroacher) but not A. greggii or L. fremontii (non-encroachers) is encroaching in grasslands because the former species has higher water and light utilization efficiencies (instantaneous water use efficiency, instantaneous light use efficiency, and Fv/Fm). The extremely high carotenoid and total antioxidant capacity in its leaves appears to help the shrub L. tridentata (encroacher) survive high ambient oxidative damage caused by both drought and high light stresses in this grassland. The two C₄ grass species, B. curtipendula and B. barbata, grow well in the arid ecosystem but may be susceptible to disturbances.     

Resource economics and coordination among above- and below-ground functional traits of three dominant shrubs from the Chilean coastal desert

Aims Plant functional traits determine how plants respond to environmental factors and influence ecosystem processes. Among them, root traits and analyses of relations between above and below-ground traits in natural communities are scarce. Methods we characterized a set of above- and below-ground traits of three dominant shrub species in a semiarid shrub-steppe that had contrasting leaf phenological habits (deciduous, semideciduous and evergreen). We analysed if there was coordination among above- and below-ground resource economics patterns: i.e. patterns of biomass allocation, construction costs and lifespan.Important findings Above- and below-ground traits and their resource economics relations pointed to species-specific functional strategies to cope with drought and poor soils and to a species ranking of fast to slow whole-plant strategies in terms of resource uptake, biomass construction costs and turnover. The deciduous shrub, Proustia cuneifolia, had relatively deep and even distribution of roots, and high proportion of short-lived tissues of low C construction costs: it had high fine to coarse root and high leaf-to-stem biomass ratios, high specific leaf area (SLA), and stems of low wood density. This strategy allows Proustia to maximize and coordinate above- and below-ground resources uptake as long as the most limiting factor (water) is available, but at the cost of having relative high plant biomass turnover. The evergreen Porlieria chilensis, instead, displayed a more conservative and slow strategy in terms of resource economics. It had ~80% of the roots in the 40cm topsoil profile, low proportion of fine compared with coarse roots and low leaf-to-stem ratios, low SLA and stems of high wood density, i.e. it invested in C costly tissues that, overall, persist longer but probably at the cost of having lower plant resource uptake rates. Traits in the semideciduous Adesmia bedwellii were in between these two functional extremes. Our results revealed high functional diversity and above- and below-ground complementarity in resource economics among these three codominant species in the Chilean coastal desert.     

基于系统发育及功能性状的不同坡向荒漠植物群落构建研究——以博湖县沙化封禁保护区为例

荒漠植物群落构建机制的研究有助于荒漠生态系统植物资源的保护及系统平衡稳定的维持。基于系统发育与功能性状相结合的方法,以博湖县沙化封禁保护区植物群落为研究对象,在研究区内纵向沙垄的不同坡向上(丘间、阴坡、阳坡)设置样方,进行植物群落物种功能性状和土壤因子的调查与测定,通过检验植物群落物种功能性状的系统发育信号,分析不同坡向植物群落物种系统发育结构和功能结构的表现模式,利用主成分分析(PCA)和线性回归模型(Linear regression model)筛选出影响物种共存的环境因子,进而揭示研究区干旱荒漠生态系统植物群落物种共存的驱动因素。结果表明：(1)研究区植被主要以耐旱的灌木和藜科草本植物为优势种;不同坡向土壤因子具有异质性,丘间、阴坡土壤养分、水分更为丰富。(2)研究区样地植物群落物种10个功能性状指标的系统发育信号K值均小于1,说明物种功能性状受系统进化影响较小,物种功能性状未表现出系统发育保守性。(3)不同坡向系统发育结构均趋于发散,限制相似性在植物分布中占主导作用;丘间和阴坡上较丰富的土壤肥力是物种功能结构发散的主要原因,阳坡物种功能结构表现为聚集效应,生境过滤为其驱动因素...     

Nutrient uptake and gas exchange of Great Basin plants provide insight into drought adaptations and coexistence

植物的养分吸收和气体交换为干旱适应和物种共存带来的启示 尽管气候变化很可能会导致干旱生态系统的降水量变化幅度增大，但沙漠灌木群落对降水变化的响应模式尚不清楚。因为适应干旱的植物具有多种生存机制以利于其物种的共存，所以认识沙漠灌木群落对降水变化的响应具有重要的意义。我们在美国大盆地地区(美国加利福尼亚州欧文斯谷)开展了一项同质园实验，对8种干旱适应性植物(其中包括了禾本科植物、灌木和杂类草植物)在3种不同夏季降水 量(分别为每月1.3、2.6和3.9 cm)的响应进行了测定。检测了上述植物在矿物养分吸收(碳、氮、磷、钾、 钙、镁、锰、铜、硼、锌、铁和钠)和气体交换参数(光合速率和气孔导度)方面的变化。研究结果显示， 两种禾本科植物[鼠尾粟草(Sporobolus airoides)和匍匐野麦赖草(Leymus triticoides)]与一种耐盐灌木物种 [密叶滨藜(Atriplex confertifolia)]在水分供给增加时，光合速率和/或气孔导度增加。在这8个物种中，有 5个物种表现出了水分供给与营养物质吸收之间的显著相关性。光合速率更高的三齿蒿(Artemisia tridentata)含有更多的钾、铜和硼，而光合速率更高的北极灯心草(Juncus arcticus)具有更高的镁和铁含量 以及更低的钠含量。北极灯心草以及3种适盐性物种[密叶滨藜、盐草(Distichlis spicata)和鼠尾粟草]在气孔导度和营养素浓度方面表现出了相关性。这些结果表明，干旱适应性物种之间对水分增多情形的生理响应机制的差异以及相关的营养吸收策略可能有助于它们在夏季雨水增多时的相互共存。     

A common tendency for phylogenetic overdispersion in mammalian assemblages

Competition has long been proposed as an important force in structuring mammalian communities. Although early work recognized that competition has a phylogenetic dimension, only with recent increases in the availability of phylogenies have true phylogenetic investigations of mammalian community structure become possible. We test whether the phylogenetic structure of 142 assemblages from three mammalian clades (New World monkeys, North American ground squirrels and Australasian possums) shows the imprint of competition. The full set of assemblages display a highly significant tendency for members to be more distantly related than expected by chance (phylogenetic overdispersion). The overdispersion is also significant within two of the clades (monkeys and squirrels) separately. This is the first demonstration of widespread overdispersion in mammal assemblages and implies an important role for either competition between close relatives where traits are conserved, habitat filtering where distant relatives share convergent traits, or both.     

How soil and elevation shape local plant biodiversity in a Mediterranean hotspot

Elucidating how evolutionary and ecological factors drive the assemblage of communities in biodiversity hotspots remains an important challenge. This currently impedes our ability to predict the responses of communities to the ongoing global changes in these major world’s biodiversity reservoirs. Here, we focus on the Sierra Nevada mountain range, a core region of the Baetic-Rifan biodiversity hotspot in the western Mediterranean, and explore the relative importance of soil properties and elevation in shaping phylogenetic and functional diversity of shrub communities. We recorded the total number of each species in community transects across elevation gradients and contrasting soil conditions, and measured some ecologically relevant functional traits (specific leaf area, leaf carbon:nitrogen ratio, plant height and blooming duration). Phylogenetic distances among species were inferred from a genus-level time-calibrated molecular phylogeny. Elevation was the main factor predicting phylogenetic and functional alpha diversity of plant communities. Species in high-elevation communities were phylogenetically distant but functionally similar, being relatively smaller and having relatively short blooming durations, whilst species in low-elevation communities showed the opposite pattern. Beta diversity in SLA and leaf C:N ratio based on species incidences were positively correlated with a soil pH and micronutrient gradient. Specifically, communities that develop on soils of high pH and low micronutrient concentrations showed low SLA values and high leaf C:N ratios, whilst communities on soils of lower pH and high micronutrient concentrations showed the opposite pattern. We conclude that soil properties and elevation simultaneously shape the structure of Mediterranean shrub communities by differentially acting on the different dimensions of the species niches. Elevation seems to filter plant height and phenology-related traits whereas nutrient-related functional traits are more related to soil properties. Our study illustrates the primary role of environmental heterogeneity for the maintenance of diversity in Mediterranean mountain ecosystems.     

Functional and phylogenetic approaches reveal the evolution of diversity in a hyper diverse biota

Ant communities in tropical forests may be governed by varying assembly mechanisms, depending on the particular habitat investigated. We compared phylogenetic diversity and structure across two forest biomes (dry and humid) and two vertical layers (arboreal and terricolous) in ant communities in Madagascar, and assessed the influence of invasive species on this community structure. We estimated phylogenetic signal and correlated evolution for habitat and several functional traits and tested for conservatism in relevant functional and habitat traits. Ancestral states were reconstructed to illuminate the evolution of habitat traits. All analyses utilized phylogenies estimated from newly generated data from three nuclear markers for 290 Malagasy ant taxa. Dry forests, although lower in species richness, were found to support equally high lineage diversity as humid forests. In contrast, phylogenetic diversity was much lower in arboreal than in terricolous communities. We observed significant phylogenetic clustering in the combined humid forest and in the arboreal–humid, arboreal–dry and terricolous–humid communities, whereas the combined dry forest community was overdispersed. Among ant communities in Madagascar, overdispersion and competition therefore may be more prevalent in dry forest, and habitat filtering may be more dominant in humid forest. Excluding invasive ant species had little overall effect on community structure. All investigated traits showed low to intermediate conservatism; strong support for correlated evolution was found for increased eye size and an arboreal lifestyle. Habitat transitions from humid to dry and from terricolous to arboreal occurred more frequently, and ancestors of most lineages were predicted to be terricolous or humid‐forest adapted. We conclude that most Malagasy ant clades first colonized humid forests and subsequently transitioned into dry forests, indicating that previous hypotheses on the evolution of Madagascar's hyperdiverse biota may not apply to ants and other arthropods.