Resource diversity and provenance underpin spatial patterns in functional diversity across native and exotic species

Functional diversity metrics are increasingly used to augment or replace taxonomic diversity metrics to deliver more mechanistic insights into community structure and function. Metrics used to describe landscape structure and characteristics share many of the same limitations as taxonomy‐based metrics, particularly their reliance on anthropogenically defined typologies with little consideration of structure, management, or function. However, the development of alternative metrics to describe landscape characteristics has been limited. Here, we extend the functional diversity framework to characterize landscapes based on the diversity of resources available across habitats present. We then examine the influence of resource diversity and provenance on the functional diversities of native and exotic avian communities in New Zealand. Invasive species are increasingly prevalent and considered a global threat to ecosystem function, but the characteristics of and interactions between sympatric native and exotic communities remain unresolved. Understanding their comparative responses to environmental change and the mechanisms underpinning them is of growing importance in predicting community dynamics and changing ecosystem function. We use (i) matrices of resource use (species) and resource availability (habitats) and (ii) occurrence data for 62 native and 25 exotic species and 19 native and 13 exotic habitats in 2015 10 × 10 km quadrats to examine the relationship between native and exotic avian and landscape functional diversity. The numbers of species in, and functional diversities of, native and exotic communities were positively related. Each community displayed evidence of environmental filtering, but it was significantly stronger for exotic species. Less environmental filtering occurred in landscapes providing a more diverse combination of resources, with resource provenance also an influential factor. Landscape functional diversity explained a greater proportion of variance in native and exotic community characteristics than the number of habitat types present. Resource diversity and provenance should be explicitly accounted for when characterizing landscape structure and change as they offer additional mechanistic understanding of the links between environmental filtering and community structure. Manipulating resource diversity through the design and implementation of management actions could prove a powerful tool for the delivery of conservation objectives, be they to protect native species, control exotic species, or maintain ecosystem service provision.     

高寒草甸不同坡向植物群落物种多样性与功能多样性的关系

植物群落物种多样性与功能多样性是生态学研究的热点问题之一,研究其对于保护生物多样性和维持生态系统功能具有重要意义。采用野外群落调查方法,探讨了物种多样性与功能多样性在坡向梯度上的变化格局及其关联性。结果显示：（1）从北坡到南坡,土壤含水量、有机碳呈递减趋势;坡度、照度、土温、pH呈递增趋势;土壤全氮、全磷在西坡明显低于其他各坡向;（2）物种多样性指数均由北坡向南坡依次递减;（3）一元性状功能多样性在各坡向间的差异显著（P<0.05）,除LDMC_FDrao外,其他功能性状均为北坡大于南坡;（4）多元性状功能丰富度与功能均匀度均由北坡向南坡呈递减的趋势,各坡向的功能均匀度差异性不显著。通过相关分析与通径分析发现,功能多样性指数的主要环境决定因子与限定因子均存在差异：功能丰富度、功能均匀度主要环境限定因子为pH,功能离散度主要环境限定因子为土温;功能离散度主要环境决定因子为土壤含水量;（5）物种多样性指数与功能丰富度呈正线性相关,与功能离散度呈负线性相关,而与功能均匀度不相关。     

Phylogenetic patterns differ for native and exotic plant communities across a richness gradient in Northern California

Aim Increasingly, ecologists are using evolutionary relationships to infer the mechanisms of community assembly. However, modern communities are being invaded by non‐indigenous species. Since natives have been associated with one another through evolutionary time, the forces promoting character and niche divergence should be high. On the other hand, exotics have evolved elsewhere, meaning that conserved traits may be more important in their new ranges. Thus, co‐occurrence over sufficient time‐scales for reciprocal evolution may alter how phylogenetic relationships influence assembly. Here, we examined the phylogenetic structure of native and exotic plant communities across a large‐scale gradient in species richness and asked whether local assemblages are composed of more or less closely related natives and exotics and whether phylogenetic turnover among plots and among sites across this gradient is driven by turnover in close or distant relatives differentially for natives and exotics. Location Central and northern California, USA. Methods We used data from 30 to 50 replicate plots at four sites and constructed a maximum likelihood molecular phylogeny using the genes: matK, rbcl, ITS1 and 5.8s. We compared community‐level measures of native and exotic phylogenetic diversity and among‐plot phylobetadiversity. Results There were few exotic clades, but they tended to be widespread. Exotic species were phylogenetically clustered within communities and showed low phylogenetic turnover among communities. In contrast, the more species‐rich native communities showed higher phylogenetic dispersion and turnover among sites. Main conclusions The assembly of native and exotic subcommunities appears to reflect the evolutionary histories of these species and suggests that shared traits drive exotic patterns while evolutionary differentiation drives native assembly. Current invasions appear to be causing phylogenetic homogenization at regional scales.     

Phylogenetic diversity,trait diversity and niches: species assembly of ferns along a tropical elevational gradient

Aim To analyse the structure of pteridophyte assemblages, based on phylogenetic relatedness and trait properties, along an elevational gradient. Ecological theory predicts that co‐occurring species may be: randomly selected from a regional pool; ecologically sorted so that they are functionally different hence resulting in reduced competition (overdispersion); or functionally similar as an adaptation to specific ecological conditions (clustering). Location Braulio Carrillo National Park and Cerro de la Muerte, Costa Rica, Central America. Methods We used an empirical dataset of the quantitative pattern of species occurrences and individual numbers of ferns within 156 plots along a tropical elevational gradient to test whether directed ecological sorting might cause deviations in patterns of trait and phylogenetic diversity. Mean pairwise distances of species based on phylogenetic and trait properties were compared with two different sets of null assemblages, one maintaining species frequency distributions (constrained) and one not (unconstrained). Results Applying different null models resulted in varying degrees of overdispersion and clustering, but overall patterns of deviation from random expectations remained the same. Contrary to theoretical predictions, phylogenetic and trait diversity were relatively independent from one another. Phylogenetic diversity showed no patterns along the elevational gradient, whereas trait diversity showed significant trends for epiphytes. Main conclusions Under stressful environmental conditions (drought at low elevations and frost at high elevations), epiphytic fern assemblages tended to be clustered with respect to trait characteristics, which suggests environmental filtering. Conversely, under less extreme environmental conditions (middle of the transect), the sorting was biased towards high differentiation (overdispersion), presumably because of interspecific competition and trait shifts among closely related species (character displacement).     

Active versus passive restoration of tallgrass prairie in the U.S. Midwest: plant species diversity and assemblage,net primary production and soil carbon sequestration

We investigated the plant species diversity, community assemblage, net primary production and soil carbon sequestration in an old field (OF), which went through passive restoration with spontaneous secondary succession, and a restored prairie (RP), which went through active restoration with reintroduction of native plants. The passive restoration in OF did not attain as high diversity and richness of plant species as did in RP. Our NMS (nonmetric multidimensional scaling) ordination revealed a clear divergence of RP and OF vegetation with dissimilar species compositions to separate paths of succession trajectory. The spontaneous succession in OF has made very little progress due to a potentially strong inhibitory priority effect of invasive plants. The belowground biomass in the high-diversity RP was 1.3× higher than the low-diversity OF. We found no measurable difference in soil C sequestration between RP and OF at this time, possibly due to edaphic factors, lack of legumes, or both. Human intervention is needed for restoring abandoned croplands—highly disturbed, fragmented and isolated habitats—to tallgrass prairies in the U.S. Midwest. Our recommended intervention includes but is not limited to removal of exotic plants, further augmentation of native plants (particularly legumes), and periodic burns.     

Grassland type and seasonal effects have a bigger influence on plant functional and taxonomical diversity than prairie dog disturbances in semiarid grasslands

1. Prairie dogs (Cynomys sp.) are considered keystone species and ecosystem engineers for their grazing and burrowing activities (summarized here as disturbances). As climate changes and its variability increases, the mechanisms underlying organisms'' interactions with their habitat will likely shift. Understanding the mediating role of prairie dog disturbance on vegetation structure, and its interaction with environmental conditions through time, will increase knowledge on the risks and vulnerability of grasslands.
2. Here, we compared how plant taxonomical diversity, functional diversity metrics, and community‐weighted trait means (CWM) respond to prairie dog C. mexicanus disturbance across grassland types and seasons (dry and wet) in a priority conservation semiarid grassland of Northeast Mexico.
3. Our findings suggest that functional metrics and CWM analyses responded to interactions between prairie dog disturbance, grassland type and season, whilst species diversity and cover measures were less sensitive to the role of prairie dog disturbance. We found weak evidence that prairie dog disturbance has a negative effect on vegetation structure, except for minimal effects on C4 and graminoid cover, but which depended mainly on season. Grassland type and season explained most of the effects on plant functional and taxonomic diversity as well as CWM traits. Furthermore, we found that leaf area as well as forb and annual cover increased during the wet season, independent of prairie dog disturbance.
4. Our results provide evidence that grassland type and season have a stronger effect than prairie dog disturbance on the vegetation of this short‐grass, water‐restricted grassland ecosystem. We argue that focusing solely on disturbance and grazing effects is misleading, and attention is needed on the relationships between vegetation and environmental conditions which will be critical to understand semiarid grassland dynamics under future climate change conditions in the region.

     

A dimmer shade of pale: revealing the faint signature of local assembly processes on the structure of strongly filtered plant communities

Trait‐based ecology suggests that abiotic filtering is the main mechanism structuring the regional species pool in different subsets of habitat‐specific species. At more local spatial scales, other ecological processes may add on giving rise to complex patterns of functional diversity (FD). Understanding how assembly processes operating on the habitat‐specific species pools produce the locally observed plant assemblages is an ongoing challenge. Here, we evaluated the importance of different processes to community assembly in an alpine fellfield, assessing its effects on local plant trait FD. Using classical randomization tests and linear mixed models, we compared the observed FD with expectations from three null models that hierarchically incorporate additional assembly constraints: stochastic null models (random assembly), independence null models (each species responding individual and independently to abiotic environment), and co‐occurrence null models (species responding to environmental variation and to the presence of other species). We sampled species composition in 115 quadrats across 24 locations in the central Pyrenees (Spain) that differed in soil conditions, solar radiation and elevation. Overall, the classical randomization tests were unable to find differences between the observed and expected functional patterns, suggesting that the strong abiotic filters that sort out the flora of extreme regional environments blur any signal of other local processes. However, our approach based on linear mixed models revealed the signature of different ecological processes. In the case of seed mass and leaf thickness, observed FD significantly deviated from the expectations of the stochastic model, suggesting that fine‐scale abiotic filtering and facilitation can be behind these patterns. Our study highlights how the hierarchical incorporation of ecological additional constraints may shed light on the dim signal left by local assembly processes in alpine environments.     

养分与水分添加对荒漠草地植物群落结构和物种多样性的影响

为进一步了解养分添加和水分添加对干旱区草地植物多样性的影响, 2009-2011年5月15日, 对准噶尔盆地荒漠草地进行养分和水分添加, 2009-2012年5月25日进行植被调查, 研究群落结构与植物多样性对养分N、P、K与水分(雨、雪)添加的响应, 得出以下结果: (1)添加肥、水后, 荒漠草地植物群落结构发生了变化, 物种数由肥、水添加前的17种减少到添加后的11种, 减少了35.3%, 禾草类植物数目增加, 十字花科植物数量下降; (2)通过裂区试验方差分析, 2009年和2010年, 养分主效应对物种丰富度、Simpson指数、Shannon-Wiener指数、Pielou均匀度指数的影响不显著, 水分主效应和肥水交互作用对以上4个植物多样性指数的影响也不显著; (3) 2012年, 养分主效应对物种丰富度影响显著(p < 0.05), 养分添加降低了荒漠草地物种丰富度, 而水分作用、肥水交互作用对物种丰富度的影响均不显著; 肥水交互作用对植物Simpson指数、Shannon-Wiener指数的影响显著(p < 0.05), 而养分添加、水分添加对其影响亦不显著; (4)荒漠草地植物的Simpson指数、Shannon-Wiener指数、Pielou均匀度指数在年际间呈上升趋势。     

控制降水梯度对荒漠草原优势植物叶功能性状及土壤养分的影响

探究植物叶功能性状随降水梯度的变化规律,对揭示干旱区优势植物对环境变化的响应和适应策略至关重要。以盐池荒漠草原为研究对象,采用遮雨棚和喷灌系统控制降水梯度,分析了优势植物蒙古冰草（Agropyron mongolicum）、短花针茅（Stipa breviflora）及达乌里胡枝子（Lespedeza davurica）叶功能性状变异,以及土壤水分、养分和微生物特性与响应性状间的相关关系。结果表明：HW（增水50%）处理下3个植物LA（叶面积）、LDMC（干物质含量）显著增大,LW处理（减水50%）下短花针茅和达乌里胡枝子LA、LDMC显著减小,降水处理对短花针茅和达乌里胡枝子SLA（比叶面积）影响不显著,LW处理显著提高了蒙古冰草SLA;LW处理显著提高了蒙古冰草和短花针茅LNC（叶氮含量）和LPC（叶磷含量）;HW显著降低了土壤C、N含量,LW和HW均显著减少了真菌数量,而放线菌数量、微生物生物量C、N显著增加;3种优势植物LA均与土壤水分显著正相关,蒙古冰草和短花针茅通过提高SLA、LNC及LNP来适应干旱生境,蒙古冰草和短花针茅LNC及LNP是表征土壤P、微生物生物量有效性的关键指标,达乌里胡枝子通过自我调节养分利用策略来适应C、N、P含量和微生物活性较低的生境,从而决定其在群落中的优势地位。     

高寒草甸植物物种丧失对草原毛虫的影响

植物多样性是调控食物网结构和生态系统功能最重要的生物因素, 植物多样性丧失深刻影响食草动物, 但由于小型食草动物种群数量波动明显、统计随机性较大等困难, 我们对植物多样性丧失如何影响小型食草动物依然知之甚少。基于在青藏高原高寒草甸设置的长期植物物种剔除试验, 本研究于2016-2020年7-8月连续调查了植物物种剔除各处理中草原毛虫(Gynaephora alpherakiif)的数量, 分析了植物物种及功能群丧失对草原毛虫的影响。结果表明, 虽然时空差异及统计随机性是影响草原毛虫数量变化的主要因素, 但植物物种剔除介导的群落差异对草原毛虫数量的影响依然显著: (1)在各观测时段, 优势种线叶嵩草(Kobresia capillifolia)的丧失导致群落中草原毛虫数量显著减少; 禾草类物种丧失也会减少草原毛虫数量, 但其影响仅在8月显著; (2)杂类草物种丧失通过增加群落中禾草物种多度, 可增加草原毛虫数量; 豆科物种丧失使莎草增多, 也会增加草原毛虫数量; (3)各植物功能群部分物种剔除并未显著影响草原毛虫数量。本研究证实了高寒草甸中草原毛虫数量会因优势植物嵩草和禾草的多度减少或禾草物种丧失而显著减少, 但群落总生物量、个体数和物种丰富度、豆科多度以及各功能群植物同比减少, 都对草原毛虫数量没有明显影响。这些结果说明在随机作用主导下, 植物群落中的特定功能群相对多度(而非物种多样性)变化深刻影响草原毛虫适合度, 进而影响生态系功能及服务; 未来生物多样性研究及草地虫害生物防控中应更多考虑统计随机性及植物功能多样性对小型食草动物的影响。     

Environment differentially affects the functional and phylogenetic structures of plant communities in a dry evergreen Afromontane tropical forest

Testing how local environmental conditions influence plant community assembly is important to understand the underlying mechanisms that promote and/or maintain biodiversity. Functional traits are used to find the broad spectrum of resource use strategies that plants use to respond to environmental variation. The patterns and drivers of plant community assembly through the lens of traits and phylogeny; however, remain to be studied in a uniquely biodiversity rich but poorly known fragmented dry Afromontane forest of Ethiopia. Here, we combined trait and community phylogenetic data from thirty sampling plots of 20 × 20 m size to determine the functional and phylogenetic structures and their drivers in a fragmented, human-dominated dry evergreen Afromontane forest. We found phylogenetic and functional clustering of plants in which the effect of environment was found to be trait specific. A weak phylogenetic signal for traits was detected suggesting that species resource use strategies may not be inferred using species phylogenetic distance. Additionally, we found functional traits to be weak in predicting species abundance distribution. Overall, while this study shows a non-random community assembly pattern, it also highlights the importance of deterministic processes being trait specific.     

不同更新方式对林地植物群落特种多样性的影响

本文就人工林经营中的三种更新方式对植物群落中物种多样性的影响进行研究。结果表明,1200m^2样地物种丰富度为：天然更新159种,人促更新130种,人工造林94种;多样性指数（Dsh）分别为4.3004、3.9283、3.5048;多样性均匀度指数(Jsh)分别为0.8484、0.8070、0.7714。人工造林的营林干扰是物种丧失和林分物种多样性下降的主要原因。     

Relationship between plant species diversity and soil microbial functional diversity along a longitudinal gradient in temperate grasslands of Hulunbeir,Inner Mongolia,China

Numerous experiments have been established to examine the effect of plant diversity on the soil microbial community. However, the relationship between plant diversity and microbial functional diversity along broad spatial gradients at a large scale is still unexplored. In this paper, we examined the relationship of plant species diversity with soil microbial biomass C, microbial catabolic activity, catabolic diversity and catabolic richness along a longitudinal gradient in temperate grasslands of Hulunbeir, Inner Mongolia, China. Preliminary detrended correspondence analysis (DCA) indicated that plant composition showed a significant separation along the axis 1, and axis 1 explained the main portion of variability in the data set. Moreover, DCA-axis 1 was significantly correlated with soil microbial biomass C (r = 0.735, P = 0.001), microbial catabolic activity (average well color development; r = 0.775, P < 0.001) and microbial functional diversity (catabolic diversity: r = 0.791, P < 0.001 and catabolic richness: r = 0.812, P < 0.001), which suggested thatsome relationship existed between plant composition and the soil microbial community along the spatial gradient at a large scale. Soil microbial biomass C, microbial catabolic activity, catabolic diversity and catabolic richness showed a significant, linear increase with greater plant species richness. However, many responses that we observed could be explained by greater aboveground plant biomass associated with higher levels of plant diversity, which suggested that plant diversity impacted the soil microbial community mainly through increases in plant production.     

Human land use promotes the abundance and diversity of exotic species on Caribbean islands

Human land use causes major changes in species abundance and composition, yet native and exotic species can exhibit different responses to land use change. Native populations generally decline in human‐impacted habitats while exotic species often benefit. In this study, we assessed the effects of human land use on exotic and native reptile diversity, including functional diversity, which relates to the range of habitat use strategies in biotic communities. We surveyed 114 reptile communities from localities that varied in habitat structure and human impact level on two Caribbean islands, and calculated species richness, overall abundance, and evenness for every plot. Functional diversity indices were calculated using published trait data, which enabled us to detect signs of trait filtering associated with impacted habitats. Our results show that environmental variation among sampling plots was explained by two Principal Component Analysis (PCA) ordination axes related to habitat structure (i.e., forest or nonforest) and human impact level (i.e., addition of man‐made constructions such as roads and buildings). Several diversity indices were significantly correlated with the two PCA axes, but exotic and native species showed opposing responses. Native species reached the highest abundance in forests, while exotic species were absent in this habitat. Human impact was associated with an increase in exotic abundance and species richness, while native species showed no significant associations. Functional diversity was highest in nonforested environments on both islands, and further increased on St. Martin with the establishment of functionally unique exotic species in nonforested habitat. Habitat structure, rather than human impact, proved to be an important agent for environmental filtering of traits, causing divergent functional trait values across forested and nonforested environments. Our results illustrate the importance of considering various elements of land use when studying its impact on species diversity and the establishment and spread of exotic species.     

The effects of human disturbance on the species composition,species diversity and functional diversity of a Miombo woodland in northern Malawi

Anthropogenic disturbances have serious impacts on ecosystems across the world. Understanding the effects of disturbance on woodlands, especially in regions where local people depend on these natural resources, is essential for sustainable natural resource management and biodiversity conservation. In this study, we evaluated the effects of anthropogenic disturbance, specifically selective logging of Brachystegia floribunda, on woodlands by comparing species composition, species diversity and functional diversity of woody plants between disturbed and undisturbed woodlands. We combined species data and functional trait data for leaves, fruits and other traits related to resource and disturbance responses to calculate functional indices (functional richness, evenness and divergence) and community‐weighted means of each trait. Shifts in taxonomic species composition were analysed using nonmetric multi‐dimensional scaling. Species composition differed significantly between disturbed and undisturbed woodlands. Tree density was greater in disturbed woodlands, whereas evenness, functional evenness and functional divergence were greater in undisturbed woodlands. In terms of forest cover, selective logging of B. floribunda appeared to have little impact on Miombo woodlands, but some shifts in functional traits, such as the shift from a deciduous to evergreen phenology, may increase the vulnerability of these ecosystems to environmental change, especially drought.     

Temporal changes in the dominance of tree functional traits,but no changes in species diversity during woody plant encroachment in a Brazilian savanna

Questions : Woody encroachment in savannas has been associated with changing taxonomic composition and ecosystem function. Interestingly, there is little understanding of how encroachment impacts plant functional diversity and how those changes relate to plant demography, a crucial mediator between taxonomic composition and ecosystem function. Location : Southeastern Brazil. Methods: Using a landscape scale fire suppression experiment in a diverse Brazilian savanna, we quantify how change in species composition over seven years impacted vegetative and reproductive tree functional diversity as determined by new recruits, dead and surviving trees. Results: Over seven years, tree above-ground biomass increased by 15%, while total species richness did not change. Despite minor changes, species composition remained overall similar (82%), with few species contributing significantly to plot dissimilarity over time. There were small changes in vegetative traits, where the community-weighted mean increased in maximum tree height (↑ 2.1%) and specific leaf area (↑ 5.3%), and decreased in wood density (↓ 1.3%) and bark thickness (↓ 9.4%). Changes in reproductive traits were larger than in vegetative traits, with an increase in the prevalence of monoecy (↑ 32.6%), dioecy (↑ 44.2%), large seeds (↑ 20.3%), animal-mediated seed dispersal (↑ 4.9%) and pollination by very small insects (↑ 45.5%), and a decrease in the prevalence of hermaphroditism (↓ 9%), small seeds (6.8%) and pollination by small insects (12.5%). The overall decrease in bark thickness and increase in monoecy and dioecy were mainly driven by characters of the new recruits, while the overall increase in specific leaf area (SLA) and decrease in small seeds appeared largely determined by the loss of trees possessing those traits. Conclusions: Encroachment leads to changes that are likely increasing ecosystem vulnerability to fire and drought. Further, the compositional changes observed appear to drive marked change in reproductive traits, indicating increasing dependence on animals for dispersal and reproduction. Understanding post-hoc encroachment impacts in an era of widespread pervasive encroachment is fundamental to reconciling ecosystem functions such as nutrient cycling and pollination services as there is a loss of species with open ecosystem life-history strategies. Among savannas, there remains an urgent need to understand relationships between woody cover and ecosystem function to determine thresholds in woody cover promoting resilient savanna ecosystems.