Dispersal and neutral sampling mediate contingent effects of disturbance on plant beta‐diversity: a meta‐analysis

A major challenge in ecology, conservation and global‐change biology is to understand why biodiversity responds differently to similar environmental changes. Contingent biodiversity responses may depend on how disturbance and dispersal interact to alter variation in community composition (β‐diversity) and assembly mechanisms. However, quantitative syntheses of these patterns and processes across studies are lacking. Using null‐models and meta‐analyses of 22 factorial experiments in herbaceous plant communities across Europe and North America, we show that disturbance diversifies communities when dispersal is limited, but homogenises communities when combined with increased immigration from the species pool. In contrast to the hypothesis that disturbance and dispersal mediate the strength of niche assembly, both processes altered β‐diversity through neutral‐sampling effects on numbers of individuals and species in communities. Our synthesis suggests that stochastic effects of disturbance and dispersal on community assembly play an important, but underappreciated, role in mediating biotic homogenisation and biodiversity responses to environmental change.     

若尔盖不同生境植物多样性与植物竞争强度和生态位重叠度的关系

植物多样性与植物竞争强度和生态位重叠度的关系会随环境发生变化。为探究上述关系在若尔盖地区的表现形式,于2021年8月对若尔盖地区典型的水生、湿生、湿生-中生和中生植物群落进行调查,构建了新的植物竞争强度（Competition intensity,CI）公式并进行测算,计算了植物群落的植物多样性指数（包括物种丰富度、Shannon-Weiner指数、Simpson指数和Pielou均匀度指数）和生态位重叠度（Niche overlap of species,NOS）,分析了植物群落物种多样性指数与CI和NOS的关系。结果表明：1）从水生到中生生境,植物多样性指数均呈增加趋势（P<0.05）;2）湿生-中生生境的CI显著高于湿生生境（P<0.05）,湿生生境的NOS高于水生生境（P<0.05）;CI与NOS无显著相关性,但在湿生生境中两者呈倒抛物线关系（P<0.05）。3）整体来看,植物群落的物种丰富度与CI呈抛物线关系（P<0.05）,与NOS无显著关系（P>0.05）;Shannon-Weiner指数、Simpson指数和Pielou均匀度指数均与NOS呈线性正相关（P<0.05）,与CI无显著关系（P>0.05）;从单个生境看,湿生-中生生境的Simpson指数、Shannon-Weiner指数和Pielou均匀度指数与CI呈线性负相关（P<0.05）,其余生境的上述多样性指数与CI无显著关系（P>0.05）;各生境的植物多样性指数均与NOS无显著相关性（P>0.05）。本研究表明,从水生到中生生境,若尔盖地区的植物多样性呈增加趋势,但植物多样性与物种竞争强度和生态位重叠度的关系较复杂。本研究结果有助于理解若尔盖高原植物多样性的形成机制。     

A socio‐ecological model for predicting impacts of land‐use and climate change on regional plant diversity in the Austrian Alps

Climate and land‐use change jointly affect the future of biodiversity. Yet, biodiversity scenarios have so far concentrated on climatic effects because forecasts of land use are rarely available at appropriate spatial and thematic scales. Agent‐based models (ABMs) represent a potentially powerful but little explored tool for establishing thematically and spatially fine‐grained land‐use scenarios. Here, we use an ABM parameterized for 1,329 agents, mostly farmers, in a Central European model region, and simulate the changes to land‐use patterns resulting from their response to three scenarios of changing socio‐economic conditions and three scenarios of climate change until the mid of the century. Subsequently, we use species distribution models to, first, analyse relationships between the realized niches of 832 plant species and climatic gradients or land‐use types, respectively, and, second, to project consequent changes in potential regional ranges of these species as triggered by changes in both the altered land‐use patterns and the changing climate. We find that both drivers determine the realized niches of the studied plants, with land use having a stronger effect than any single climatic variable in the model. Nevertheless, the plants' future distributions appear much more responsive to climate than to land‐use changes because alternative future socio‐economic backgrounds have only modest impact on land‐use decisions in the model region. However, relative effects of climate and land‐use changes on biodiversity may differ drastically in other regions, especially where landscapes are still dominated by natural or semi‐natural habitat. We conclude that agent‐based modelling of land use is able to provide scenarios at scales relevant to individual species distribution and suggest that coupling ABMs with models of species' range change should be intensified to provide more realistic biodiversity forecasts.     

植物群落构建的生态过滤机制研究进展

生物多样性的形成和维持机制,即群落构建机制,一直以来都是群落生态学研究的核心问题。植物群落构建的确定性过程主要是生态过滤机制(包括环境过滤和生物过滤,其中生物过滤包括种间竞争和种内功能性状变异)作用的结果。学者们构建了大量的理论、方法、模型来解释和验证生态过滤机制对群落构建的影响,并取得了显著的成果。然而,关于生态过滤机制在不同尺度的作用、生态过滤机制的各要素分解和量化等方面的研究仍有诸多疑问。重点综述了环境过滤、种间竞争和种内功能性状变异的最新研究进展,并指出了现有研究的不足之处。在未来的研究中,应注重生态过滤机制的各要素分解和量化,加强研究手段的综合运用,关注时空动态变化对植物群落构建的影响,重视对不同植物群落构建机制的共性和个性特征的认识,同时强调与其他生态过程、群落构建机制的整合。通过这些尝试,有助于人们更好的理解植物群落构建过程中的生态过滤机制的作用。     

Short‐term harvesting of biomass from conservation grasslands maintains plant diversity

High yields are a priority in managing biomass for renewable energy, but the environmental impacts of various feedstocks and production systems should be equally considered. Mixed‐species, perennial grasslands enrolled in conservation programs are being considered as a source of biomass for renewable energy. Conservation grasslands are crucial in sustaining native biodiversity throughout the US Upper Midwest, and the effects of biomass harvest on biodiversity are largely unknown. We measured the effect of late‐season biomass harvest on plant community composition in conservation grasslands in three regions of Minnesota, USA from 2009 to 2012. Temporal trends in plant species composition within harvested grasslands were compared to unharvested grasslands using mixed effects models. A before‐after control‐impact approach using effect sizes was applied to focus on pre‐ and postharvest conditions. Production‐scale biomass harvest did not affect plant species richness, species or functional group diversity, nor change the relative abundance of the main plant functional groups. Differences in the relative abundances of plant functional groups were observed across locations; and at some locations, changed through time. The proportion of non‐native species remained constant, while the proportion of noxious weeds decreased through time in both harvested and unharvested grasslands at the central location. Ordination revealed patterns in species composition due to location, but not due to harvest treatment. Therefore, habitat and bioenergy characteristics related to grassland plant communities are not expected to change due to short‐term or intermittent late‐season biomass harvest.     

Topographically controlled thermal‐habitat differentiation buffers alpine plant diversity against climate warming

Aim We aim to: (1) explore thermal habitat preferences in alpine plant species across mosaics of topographically controlled micro‐habitats; (2) test the predictive value of so‐called ‘indicator values’; and (3) quantify the shift in micro‐habitat conditions under the influence of climate warming. Location Alpine vegetation 2200–2800 m a.s.l., Swiss central Alps. Methods High‐resolution infra‐red thermometry and large numbers of small data loggers were used to assess the spatial and temporal variation of plant‐surface and ground temperatures as well as snow‐melt patterns for 889 plots distributed across three alpine slopes of contrasting exposure. These environmental data were then correlated with Landolt indicator values for temperature preferences of different plant species and vegetation units. By simulating a uniform 2 K warming we estimated the changes in abundance of micro‐habitat temperatures within the study area. Results Within the study area we observed a substantial variation between micro‐habitats in seasonal mean soil temperature (ΔT = 7.2 K), surface temperature (ΔT = 10.5 K) and season length (>32 days). Plant species with low indicator values for temperature (plants commonly found in cool habitats) grew in significantly colder micro‐habitats than plants with higher indicator values found on the same slope. A 2 K warming will lead to the loss of the coldest habitats (3% of current area), 75% of the current thermal micro‐habitats will be reduced in abundance (crowding effect) and 22% will become more abundant. Main conclusions Our results demonstrate that the topographically induced mosaics of micro‐climatic conditions in an alpine landscape are associated with local plant species distribution. Semi‐quantitative plant species indicator values based on expert knowledge and aggregated to community means match measured thermal habitat conditions. Metre‐scale thermal contrasts significantly exceed IPCC warming projections for the next 100 years. The data presented here thus indicate a great risk of overestimating alpine habitat losses in isotherm‐based model scenarios. While all but the species depending on the very coldest micro‐habitats will find thermally suitable ‘escape’ habitats within short distances, there will be enhanced competition for those cooler places on a given slope in an alpine climate that is 2 K warmer. Yet, due to their topographic variability, alpine landscapes are likely to be safer places for most species than lowland terrain in a warming world.     

Disentangling vegetation diversity from climate–energy and habitat heterogeneity for explaining animal geographic patterns

Broad‐scale animal diversity patterns have been traditionally explained by hypotheses focused on climate–energy and habitat heterogeneity, without considering the direct influence of vegetation structure and composition. However, integrating these factors when considering plant–animal correlates still poses a major challenge because plant communities are controlled by abiotic factors that may, at the same time, influence animal distributions. By testing whether the number and variation of plant community types in Europe explain country‐level diversity in six animal groups, we propose a conceptual framework in which vegetation diversity represents a bridge between abiotic factors and animal diversity. We show that vegetation diversity explains variation in animal richness not accounted for by altitudinal range or potential evapotranspiration, being the best predictor for butterflies, beetles, and amphibians. Moreover, the dissimilarity of plant community types explains the highest proportion of variation in animal assemblages across the studied regions, an effect that outperforms the effect of climate and their shared contribution with pure spatial variation. Our results at the country level suggest that vegetation diversity, as estimated from broad‐scale classifications of plant communities, may contribute to our understanding of animal richness and may be disentangled, at least to a degree, from climate–energy and abiotic habitat heterogeneity.     

A gradient of nutrient enrichment reveals nonlinear impacts of fertilization on Arctic plant diversity and ecosystem function

Rapid environmental change at high latitudes is predicted to greatly alter the diversity, structure, and function of plant communities, resulting in changes in the pools and fluxes of nutrients. In Arctic tundra, increased nitrogen (N) and phosphorus (P) availability accompanying warming is known to impact plant diversity and ecosystem function; however, to date, most studies examining Arctic nutrient enrichment focus on the impact of relatively large (>25x estimated naturally occurring N enrichment) doses of nutrients on plant community composition and net primary productivity. To understand the impacts of Arctic nutrient enrichment, we examined plant community composition and the capacity for ecosystem function (net ecosystem exchange, ecosystem respiration, and gross primary production) across a gradient of experimental N and P addition expected to more closely approximate warming‐induced fertilization. In addition, we compared our measured ecosystem CO₂ flux data to a widely used Arctic ecosystem exchange model to investigate the ability to predict the capacity for CO₂ exchange with nutrient addition. We observed declines in abundance‐weighted plant diversity at low levels of nutrient enrichment, but species richness and the capacity for ecosystem carbon uptake did not change until the highest level of fertilization. When we compared our measured data to the model, we found that the model explained roughly 30%–50% of the variance in the observed data, depending on the flux variable, and the relationship weakened at high levels of enrichment. Our results suggest that while a relatively small amount of nutrient enrichment impacts plant diversity, only relatively large levels of fertilization—over an order of magnitude or more than warming‐induced rates—significantly alter the capacity for tundra CO₂ exchange. Overall, our findings highlight the value of measuring and modeling the impacts of a nutrient enrichment gradient, as warming‐related nutrient availability may impact ecosystems differently than single‐level fertilization experiments.     

Beta‐diversity in temperate and tropical forests reflects dissimilar mechanisms of community assembly

Site‐to‐site variation in species composition (β‐diversity) generally increases from low‐ to high‐diversity regions. Although biogeographical differences in community assembly mechanisms may explain this pattern, random sampling effects can create this pattern through differences in regional species pools. Here, we compared assembly mechanisms between spatially extensive networks of temperate and tropical forest plots with highly divergent species pools (46 vs. 607 species). After controlling for sampling effects, β‐diversity of woody plants was similar and higher than expected by chance in both forests, reflecting strong intraspecific aggregation. However, different mechanisms appeared to explain aggregation in the two forests. In the temperate forest, aggregation reflected stronger environmental correlations, suggesting an important role for species‐sorting (e.g. environmental filtering) processes, whereas in the tropics, aggregation reflected stronger spatial correlations, more likely reflecting dispersal limitation. We suggest that biogeographical differences in the relative importance of different community assembly mechanisms contribute to these striking gradients in global biodiversity.     

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。     

Factors determining mammal species richness on habitat islands and isolates: habitat diversity, disturbance, species interactions and guild assembly rules

• 1 For over three decades the equilibrium theory of island biogeography has galvanized studies in ecological biogeography. Studies of oceanic islands and of natural habitat islands share some similarities to continental studies, particularly in developed regions where habitat fragmentation results from many land uses. Increasingly, remnant habitat is in the form of isolates created by the clearing and destruction of natural areas. Future evolution of a theory to predict patterns of species abundance may well come from the application of island biogeography to habitat fragments or isolates.
• 2 In this paper we consider four factors other than area and isolation that influence the number and type of mammal species coexisting in one place: habitat diversity, habitat disturbance, species interactions and guild assembly rules. In all examples our data derive from mainland habitat, fragmented to differing degrees, with different levels of isolation.
• 3 Habitat diversity is seen to be a good predictor of species richness. Increased levels of disturbance produce a relatively greater decrease in species richness on smaller than on larger isolates. Species interactions in the recolonization of highly disturbed sites, such as regenerating mined sites, is analogous to island colonization. Species replacement sequences in secondary successions indicate not just how many, but which species are included. Lastly, the complement of species established on islands, or in insular habitats, may be governed by guild assembly rules. These contributions may assist in taking a renewed theory into the new millennium.

     

Community diversity outweighs effect of warming on plant colonization

Abiotic environmental change, local species extinctions and colonization of new species often co‐occur. Whether species colonization is driven by changes in abiotic conditions or reduced biotic resistance will affect community functional composition and ecosystem management. We use a grassland experiment to disentangle effects of climate warming and community diversity on plant species colonization. Community diversity had dramatic impacts on the biomass, richness and traits of plant colonists. Three times as many species colonized the monocultures than the high diversity 17 species communities (~30 vs. 10 species), and colonists collectively produced 10 times as much biomass in the monocultures than the high diversity communities (~30 vs. 3 g/m²). Colonists with resource‐acquisitive strategies (high specific leaf area, light seeds, short heights) accrued more biomass in low diversity communities, whereas species with conservative strategies accrued most biomass in high diversity communities. Communities with higher biomass of resident C4 grasses were more resistant to colonization by legume, nonlegume forb and C3 grass colonists, but not by C4 grass colonists. Compared with effects of diversity, 6 years of 3°C‐above‐ambient temperatures had little impact on plant colonization. Warmed subplots had ~3 fewer colonist species than ambient subplots and selected for heavier seeded colonists. They also showed diversity‐dependent changes in biomass of C3 grass colonists, which decreased under low diversity and increased under high diversity. Our findings suggest that species colonization is more strongly affected by biotic resistance from residents than 3°C of climate warming. If these results were extended to invasive species management, preserving community diversity should help limit plant invasion, even under climate warming.     

The importance of rare species: a trait‐based assessment of rare species contributions to functional diversity and possible ecosystem function in tall‐grass prairies

The majority of species in ecosystems are rare, but the ecosystem consequences of losing rare species are poorly known. To understand how rare species may influence ecosystem functioning, this study quantifies the contribution of species based on their relative level of rarity to community functional diversity using a trait‐based approach. Given that rarity can be defined in several different ways, we use four different definitions of rarity: abundance (mean and maximum), geographic range, and habitat specificity. We find that rarer species contribute to functional diversity when rarity is defined by maximum abundance, geographic range, and habitat specificity. However, rarer species are functionally redundant when rarity is defined by mean abundance. Furthermore, when using abundance‐weighted analyses, we find that rare species typically contribute significantly less to functional diversity than common species due to their low abundances. These results suggest that rare species have the potential to play an important role in ecosystem functioning, either by offering novel contributions to functional diversity or via functional redundancy depending on how rare species are defined. Yet, these contributions are likely to be greatest if the abundance of rare species increases due to environmental change. We argue that given the paucity of data on rare species, understanding the contribution of rare species to community functional diversity is an important first step to understanding the potential role of rare species in ecosystem functioning.     

Partitioning of beta‐diversity reveals distinct assembly mechanisms of plant and soil microbial communities in response to nitrogen enrichment

Nitrogen (N) deposition poses a serious threat to terrestrial biodiversity and alters plant and soil microbial community composition. Species turnover and nestedness reflect the underlying mechanisms of variations in community composition. However, it remains unclear how species turnover and nestedness contribute to different responses of taxonomic groups (plants and soil microbes) to N enrichment. Here, based on a 13‐year consecutive multi‐level N addition experiment in a semiarid steppe, we partitioned community β‐diversity into species turnover and nestedness components and explored how and why plant and microbial communities reorganize via these two processes following N enrichment. We found that plant, soil bacterial, and fungal β‐diversity increased, but their two components showed different patterns with increasing N input. Plant β‐diversity was mainly driven by species turnover under lower N input but by nestedness under higher N input, which may be due to a reduction in forb species, with low tolerance to soil Mn²⁺, with increasing N input. However, turnover was the main contributor to differences in soil bacterial and fungal communities with increasing N input, indicating the phenomenon of microbial taxa replacement. The turnover of bacteria increased greatly whereas that of fungi remained within a narrow range with increasing N input. We further found that the increased soil Mn²⁺ concentration was the best predictor for increasing nestedness of plant communities under higher N input, whereas increasing N availability and acidification together contributed to the turnover of bacterial communities. However, environmental factors could explain neither fungal turnover nor nestedness. Our findings reflect two different pathways of community changes in plants, soil bacteria, and fungi, as well as their distinct community assembly in response to N enrichment. Disentangling the turnover and nestedness of plant and microbial β‐diversity would have important implications for understanding plant–soil microbe interactions and seeking conservation strategies for maintaining regional diversity.     

黄土高原草地植物多样性与群落稳定性的关系及其驱动因素

植物多样性对维持生态功能的稳定发挥具有重要作用。以黄土高原不同植被带草地为研究对象,基于野外调查和实验分析,探究黄土高原不同植被带草地植物多样性与群落稳定性特征和二者之间的关系以及影响因素。结果表明：黄土高原草地群落结构特征(地上生物量、地下生物量)与植物多样性具有明显的纬度分布格局,草地植物多样性和生物量均表现出自东南向西北沿森林草原带—森林带—草原带—草原荒漠带逐渐递减趋势。森林草原带草地植物多样性和群落稳定性显著高于森林带、草原带和草原荒漠带;植物多样性与群落稳定性之间存在显著正相关关系,可以作为衡量群落稳定性的指标,其稳定性大小表现为森林草原带>森林带>草原带>草原荒漠带。降雨量是影响植物多样性和群落稳定性的主要因素,并通过改变土壤含水量影响群落稳定性。研究结果揭示了草地植物多样性与群落稳定性之间的关系及驱动机制,为维持黄土高原草地生态系统的群落稳定性提供了科学依据。     

高寒湿地植物群落的物种多样性保护及生态恢复对策

以物种组成较为复杂的青藏高原东部地区玛曲县高寒湿地为背景．从恢复生态学角度,系统地探讨了影响湿地植物群落物种多样性与生产力变化的主要因素,从不同的时间和空间尺度研究了典型样区植物群落中物种多样性与生产力的恢复机理与过程,以及生境异质性对其的影响。结果表明：在导致湿地植被退化的人类干扰诸因素中．超载放牧是主要因素。该地区超载量高达24％;其次．气候变化对湿地物种多样性与生产力也有较大影响。典型样区的恢复试验结果表明：实行围栏轮牧、控制载畜量、鼠虫害防治和建植人工草地等人工综合措施,能使样区植被得以卓有成效的恢复与保护。其中．黄河滩地的植物群落中．物种丰富度从23种／m^2上升到29种／m^2;Shannon多样性指数从3．82上升到4．62;草场生产力(地上生物量)从729．2g／m^2上升到935．38g／m^2。阳坡和阴坡样地植被也有类同的恢复效果。在以上三类样地中．以滩地的生态恢复效果最为显著。据此,我们提出了相应的湿地物种多样性保护和生态恢复对策．即：加强自然保护区建设、协调人类活动与物种多样性保护的关系、严格控制载畜量、发展人工草地等主要措施与建设。     

Trait‐based tests of coexistence mechanisms

Recent functional trait studies have shown that trait differences may favour certain species (environmental filtering) while simultaneously preventing competitive exclusion (niche partitioning). However, phenomenological trait‐dispersion analyses do not identify the mechanisms that generate niche partitioning, preventing trait‐based prediction of future changes in biodiversity. We argue that such predictions require linking functional traits with recognised coexistence mechanisms involving spatial or temporal environmental heterogeneity, resource partitioning and natural enemies. We first demonstrate the limitations of phenomenological approaches using simulations, and then (1) propose trait‐based tests of coexistence, (2) generate hypotheses about which plant functional traits are likely to interact with particular mechanisms and (3) review the literature for evidence for these hypotheses. Theory and data suggest that all four classes of coexistence mechanisms could act on functional trait variation, but some mechanisms will be stronger and more widespread than others. The highest priority for future research is studies of interactions between environmental heterogeneity and trait variation that measure environmental variables at within‐community scales and quantify species' responses to the environment in the absence of competition. Evidence that similar trait‐based coexistence mechanisms operate in many ecosystems would simplify biodiversity forecasting and represent a rare victory for generality over contingency in community ecology.