Functional diversity of avian communities increases with canopy height: From individual behavior to continental‐scale patterns

Vegetation complexity is an important predictor of animal species diversity. Specifically, taller vegetation should provide more potential ecological niches and thus harbor communities with higher species richness and functional diversity (FD). Resource use behavior is an especially important functional trait because it links species to their resource base with direct relevance to niche partitioning. However, it is unclear how exactly the diversity of resource use behavior changes with vegetation complexity. To address this question, we studied avian FD in relation to vegetation complexity along a continental‐scale vegetation gradient. We quantified foraging behavior of passerine birds in terms of foraging method and substrate use at 21 sites (63 transects) spanning 3,000 km of woodlands and forests in Australia. We also quantified vegetation structure on 630 sampling points at the same sites. Additionally, we measured morphological traits for all 111 observed species in museum collections. We calculated individual‐based, abundance‐weighted FD in morphology and foraging behavior and related it to species richness and vegetation complexity (indexed by canopy height) using structural equation modeling, rarefaction analyses, and distance‐based metrics. FD of morphology and foraging methods was best predicted by species richness. However, FD of substrate use was best predicted by canopy height (ranging 10–30 m), but only when substrates were categorized with fine resolution (17 categories), not when categorized coarsely (8 categories). These results suggest that, first, FD might increase with vegetation complexity independently of species richness, but whether it does so depends on the studied functional trait. Second, patterns found might be shaped by how finely we categorize functional traits. More complex vegetation provided larger "ecological space" with more resources, allowing the coexistence of more species with disproportionately more diverse foraging substrate use. We suggest that the latter pattern was driven by nonrandom accumulation of functionally distinct species with increasing canopy height.     

Canopy and litter ant assemblages share similar climate–species density relationships

Tropical forest canopies house most of the globe''s diversity, yet little is known about global patterns and drivers of canopy diversity. Here, we present models of ant species density, using climate, abundance and habitat (i.e. canopy versus litter) as predictors. Ant species density is positively associated with temperature and precipitation, and negatively (or non-significantly) associated with two metrics of seasonality, precipitation seasonality and temperature range. Ant species density was significantly higher in canopy samples, but this difference disappeared once abundance was considered. Thus, apparent differences in species density between canopy and litter samples are probably owing to differences in abundance–diversity relationships, and not differences in climate–diversity relationships. Thus, it appears that canopy and litter ant assemblages share a common abundance–diversity relationship influenced by similar but not identical climatic drivers.     

Nurse plants have the potential to accelerate vegetation recovery in Lapalala Wilderness old fields,South Africa

Nurse plants offer microclimates that are favourable to plant growth of understory native vegetation, thus facilitating ecological restoration in degraded old fields. This study examined the impact of three nurse plants on vegetation diversity and soil physical properties in old fields located at Lapalala Wilderness, South Africa. Vegetation surveys in plots measuring 5 m x 5 m under and outside the canopy of nurse plants in both old field and natural sites were conducted. Top soils under and outside the nurse plants canopy were collected in all plots and quantified for soil moisture, soil penetration resistance and soil water repellency. Results indicate that species diversity was high under plant canopy compared to outside plant canopy for all nurse plants. Soils under nurse plants canopy showed improved soil moisture and soil penetration resistance compared to soils outside plant canopy, but no differences were reported for soil water repellency. The study concludes that the presence of native plants under nurse plants canopy points to a positive vegetation recovery trajectory. For vegetation and soil restoration to be effective in Lapalala Wilderness old fields, nurse plants should be protected and active restoration, e.g. seeding or seedling sowing under nurse plants canopy should be considered.     

基于激光雷达数据的物种分布模拟: 以美国加州内华达山脉南部区域食鱼貂分布模拟为例

生态位模型通过拟合物种分布与环境变量之间的关系提供物种空间分布预测, 在生物多样性研究中有广泛应用。激光雷达(LiDAR)是一种新兴的主动遥感技术, 已被大量应用于森林三维结构信息的提取, 但其在物种分布模拟的应用研究比较缺乏。本研究以美国加州内华达山脉南部地区的食鱼貂(Martes pennanti)的分布模拟为例, 探索LiDAR技术在物种分布模拟中的有效性。生态位模型采用5种传统多类分类器, 包括神经网络、广义线性模型、广义可加模型、最大熵模型和多元自适应回归样条模型, 并使用正样本-背景学习(presence and background learning, PBL)算法进行模型校正; 同时对这5种模型使用加权平均进行模型集成, 作为第6个模型。此外, 一类最大熵模型也被用于模拟该物种的空间分布。模型的连续输出和二值输出分别使用AUC (area under the receiver operating characteristic curve)以及基于正样本-背景数据的评价指标F_pb进行评价。结果表明, 仅考虑气候因子(温度和降水)时, 7个模型的AUC和F_pb平均值分别为0.779和1.077; 当考虑LiDAR变量(冠层容重、枝下高、叶面积指数、高程、坡度等)后, AUC和F_pb分别为0.800和1.106。该研究表明, LiDAR数据能够提高食鱼貂空间分布的预测精度, 在物种分布模拟方面存在一定的应用价值。     

Effects of grain size and niche breadth on species distribution modeling

Scale is a vital component to consider in ecological research, and spatial resolution or grain size is one of its key facets. Species distribution models (SDMs) are prime examples of ecological research in which grain size is an important component. Despite this, SDMs rarely explicitly examine the effects of varying the grain size of the predictors for species with different niche breadths. To investigate the effect of grain size and niche breadth on SDMs, we simulated four virtual species with different grain sizes/niche breadths using three environmental predictors (elevation, aspect, and percent forest) across two real landscapes of differing heterogeneity in predictor values. We aggregated these predictors to seven different grain sizes and modeled the distribution of each of our simulated species using MaxEnt and GLM techniques at each grain size. We examined model accuracy using the AUC statistic, Pearson's correlations of predicted suitability with the true suitability, and the binary area of presence determined from suitability above the maximum true skill statistic (TSS) threshold. Habitat specialists were more accurately modeled than generalist species, and the models constructed at the grain size from which a species was derived generally performed the best. The accuracy of models in the homogenous landscape deteriorated with increasing grain size to a greater degree than models in the heterogenous landscape. Variable effects on the model varied with grain size, with elevation increasing in importance as grain size increased while aspect lost importance. The area of predicted presence was drastically affected by grain size, with larger grain sizes over predicting this value by up to a factor of 14. Our results have implications for species distribution modeling and conservation planning, and we suggest more studies include analysis of grain size as part of their protocol.     

Alien Invasive Slider Turtle in Unpredicted Habitat: A Matter of Niche Shift or of Predictors Studied?

Background

Species Distribution Models (SDMs) aim on the characterization of a species'' ecological niche and project it into geographic space. The result is a map of the species'' potential distribution, which is, for instance, helpful to predict the capability of alien invasive species. With regard to alien invasive species, recently several authors observed a mismatch between potential distributions of native and invasive ranges derived from SDMs and, as an explanation, ecological niche shift during biological invasion has been suggested. We studied the physiologically well known Slider turtle from North America which today is widely distributed over the globe and address the issue of ecological niche shift versus choice of ecological predictors used for model building, i.e., by deriving SDMs using multiple sets of climatic predictor.

Principal Findings

In one SDM, predictors were used aiming to mirror the physiological limits of the Slider turtle. It was compared to numerous other models based on various sets of ecological predictors or predictors aiming at comprehensiveness. The SDM focusing on the study species'' physiological limits depicts the target species'' worldwide potential distribution better than any of the other approaches.

Conclusion

These results suggest that a natural history-driven understanding is crucial in developing statistical models of ecological niches (as SDMs) while “comprehensive” or “standard” sets of ecological predictors may be of limited use.     

Evaluating the ecological realism of plant species distribution models with ecological indicator values

Species distribution models (SDMs) are routinely applied to assess current as well as future species distributions, for example to assess impacts of future environmental change on biodiversity or to underpin conservation planning. It has been repeatedly emphasized that SDMs should be evaluated based not only on their goodness of fit to the data, but also on the realism of the modeled ecological responses. However, possibilities for the latter are hampered by limited knowledge on the true responses as well as a lack of quantitative evaluation methods. Here we compared modeled niche optima obtained from European-scale SDMs of 1476 terrestrial vascular plant species with empirical ecological indicator values indicating the preferences of plant species for key environmental conditions. For each plant species we first fitted an ensemble SDM including three modeling techniques (GLM, GAM and BRT) and extracted niche optima for climate, soil, land use and nitrogen deposition variables with a large explanatory power for the occurrence of that species. We then compared these SDM-derived niche optima with the ecological indicator values by means of bivariate correlation analysis. We found weak to moderate correlations in the expected direction between the SDM-derived niche optima and ecological indicator values. The strongest correlation occurred between the modeled optima for growing degree days and the ecological indicator values for temperature. Correlations were weaker for SDM-derived niche optima with a more distal relationship to ecological indicator values (notably precipitation and soil moisture). Further, correlations were consistently highest for BRT, followed by GLM and GAM. Our method gives insight into the ecological realism of modeled niche optima and projected core habitats and can be used to improve SDMs by making a more informed selection of environmental variables and modeling techniques.     

Occurrence of blood-feeding terrestrial leeches (Haemadipsidae) in a degraded forest ecosystem and their potential as ecological indicators

Blood-feeding invertebrates are emerging model taxa in biodiversity assessments, both as indicators of mammal abundance and also as sources of mammal DNA for identification. Among these, terrestrial leeches arguably offer the greatest promise; they are abundant and widespread in the humid tropics, and their blood meals can be easily assayed to establish diet. Unfortunately, terrestrial leeches are understudied, with little known about their ecology and behavior. Such information is needed to evaluate their utility as ecological indicators and to account for potential sampling biases that might arise from habitat preferences. By combining occupancy modeling and thermal tolerance assays, we determined the factors affecting species occurrence in the related terrestrial brown (Haemadipsa sumatrana) and tiger leech (Haemadipsa picta), both of which are widespread in tropical forests in Southeast Asia. We sampled both species across a degraded forest landscape in Sabah, Borneo, in wet and dry seasons, associating occurrence with habitat-level metrics. We found that, for both species, detection probability increased with canopy height regardless of season. Additionally, increased vegetation heterogeneity had a strong negative influence on brown leech occurrence in the dry season, implying an interaction between vegetation structure and climate. However, we found no difference in physiological thermal tolerance (CT_MAX) between the two species. Finally, using a reduced dataset, we found a small improvement in brown leech model fit when including mammal abundance. Our results suggest that the presence of terrestrial leeches may act as useful ecological indicators of habitat quality and potentially mammalian abundance. Abstract in Indonesia is available with online material.     

Disentangling the Role of Climate,Topography and Vegetation in Species Richness Gradients

Environmental gradients (EG) related to climate, topography and vegetation are among the most important drivers of broad scale patterns of species richness. However, these different EG do not necessarily drive species richness in similar ways, potentially presenting synergistic associations when driving species richness. Understanding the synergism among EG allows us to address key questions arising from the effects of global climate and land use changes on biodiversity. Herein, we use variation partitioning (also know as commonality analysis) to disentangle unique and shared contributions of different EG in explaining species richness of Neotropical vertebrates. We use three broad sets of predictors to represent the environmental variability in (i) climate (annual mean temperature, temperature annual range, annual precipitation and precipitation range), (ii) topography (mean elevation, range and coefficient of variation of elevation), and (iii) vegetation (land cover diversity, standard deviation and range of forest canopy height). The shared contribution between two types of EG is used to quantify synergistic processes operating among EG, offering new perspectives on the causal relationships driving species richness. To account for spatially structured processes, we use Spatial EigenVector Mapping models. We perform analyses across groups with distinct dispersal abilities (amphibians, non-volant mammals, bats and birds) and discuss the influence of vagility on the partitioning results. Our findings indicate that broad scale patterns of vertebrate richness are mainly affected by the synergism between climate and vegetation, followed by the unique contribution of climate. Climatic factors were relatively more important in explaining species richness of good dispersers. Most of the variation in vegetation that explains vertebrate richness is climatically structured, supporting the productivity hypothesis. Further, the weak synergism between topography and vegetation urges caution when using topographic complexity as a surrogate of habitat (vegetation) heterogeneity.     

Division within the North American boreal forest: Ecological niche divergence between the Bicknell's Thrush (Catharus bicknelli) and Gray‐cheeked Thrush (C. minimus)

Sister species that diverged in allopatry in similar environments are expected to exhibit niche conservatism. Using ecological niche modeling and a multivariate analysis of climate and habitat data, I test the hypothesis that the Bicknell's Thrush (Catharus bicknelli) and Gray‐cheeked Thrush (C. mimimus), sister species that breed in the North American boreal forest, show niche conservatism. Three tree species that are important components of breeding territories of both thrush species were combined with climatic variables to create niche models consisting of abiotic and biotic components. Abiotic‐only, abiotic+biotic, and biotic‐only models were evaluated using the area under the curve (AUC) criterion. Abiotic+biotic models had higher AUC scores and did not over‐project thrush distributions compared to abiotic‐only or biotic‐only models. From the abiotic+biotic models, I tested for niche conservatism or divergence by accounting for the differences in the availability of niche components by calculating (1) niche overlap from ecological niche models and (2) mean niche differences of environmental values at occurrence points. Niche background similarity tests revealed significant niche divergence in 10 of 12 comparisons, and multivariate tests revealed niche divergence along 2 of 3 niche axes. The Bicknell's Thrush breeds in warmer and wetter regions with a high abundance of balsam fir (Abies balsamea), whereas Gray‐cheeked Thrush often co‐occurs with black spruce (Picea mariana). Niche divergence, rather than conservatism, was the predominant pattern for these species, suggesting that ecological divergence has played a role in the speciation of the Bicknell's Thrush and Gray‐cheeked Thrush. Furthermore, because niche models were improved by the incorporation of biotic variables, this study validates the inclusion of relevant biotic factors in ecological niche modeling to increase model accuracy.     

“一元多生态位”原理及其在棉花高产栽培中的应用

“一元多生态位”群体是指由同一个物种(品种)构成,生态元具有不同时间生态位、空间生态位、营养生态位、温度生态位或者水分生态位等．其特征为,群体培育具有目标性,种群组成具有一元性,冠层结构具有多层性,群体形成过程具有人工调控性,群体建立过程具有简单性,所形成的群体各生态元具有特定的生态位宽度、生态位重叠与生态位分离．从产量构成来看。作物“一元多生态位”群体具有群体生产能力的高效性和单株生产能力的差异性特征。     

Shape and evolution of the fundamental niche in marine Vibrio

Hutchinson''s fundamental niche, defined by the physical and biological environments in which an organism can thrive in the absence of inter-species interactions, is an important theoretical concept in ecology. However, little is known about the overlap between the fundamental niche and the set of conditions species inhabit in nature, and about natural variation in fundamental niche shape and its change as species adapt to their environment. Here, we develop a custom-made dual gradient apparatus to map a cross-section of the fundamental niche for several marine bacterial species within the genus Vibrio based on their temperature and salinity tolerance, and compare tolerance limits to the environment where these species commonly occur. We interpret these niche shapes in light of a conceptual model comprising five basic niche shapes. We find that the fundamental niche encompasses a much wider set of conditions than those strains typically inhabit, especially for salinity. Moreover, though the conditions that strains typically inhabit agree well with the strains'' temperature tolerance, they are negatively correlated with the strains'' salinity tolerance. Such relationships can arise when the physiological response to different stressors is coupled, and we present evidence for such a coupling between temperature and salinity tolerance. Finally, comparison with well-documented ecological range in V. vulnificus suggests that biotic interactions limit the occurrence of this species at low-temperature—high-salinity conditions. Our findings highlight the complex interplay between the ecological, physiological and evolutionary determinants of niche morphology, and caution against making inferences based on a single ecological factor.     

MaxEnt模型参数设置对其所模拟物种地理分布和生态位的影响——以茶翅蝽为例

【目的】生态位模型被广泛应用于入侵生物学和保护生物学研究,现有建模工具中,MaxEnt是最流行和运用最广泛的生态位模型。然而最近研究表明,基于MaxEnt模型的默认参数构建模型时,模型倾向于过度拟合,并非一定为最佳模型,尤其是在处理一些分布点较少的物种。【方法】以茶翅蝽为例,通过设置不同的特征参数、调控倍频以及背景拟不存在点数分别构建茶翅蝽的本土模型,然后将其转入入侵地来验证和比较模型,通过检测模型预测的物种对环境因子的响应曲线、潜在分布在生态空间中的生态位映射以及潜在分布的空间差异性,探讨3种参数设置对MaxEnt模型模拟物种分布和生态位的影响。【结果】在茶翅蝽的案例分析中,特征参数的设置对MaxEnt模型所模拟的潜在分布和生态位的影响最大,调控倍频的影响次之,背景拟不存在点数的影响最小。与其他特征相比,基于特征H和T的模型其响应曲线较为曲折;随着调控倍频的增加,响应曲线变得圆滑。【结论】在构建MaxEnt模型时,需要从生态空间中考虑物种的生态需求,分析模型参数对预测物种分布和生态位可能造成的影响。     

Species distribution models for invasive Eurasian watermilfoil highlight the importance of data quality and limitations of discrimination accuracy metrics

AimAvailability of uniformly collected presence, absence, and abundance data remains a key challenge in species distribution modeling (SDM). For invasive species, abundance and impacts are highly variable across landscapes, and quality occurrence and abundance data are critical for predicting locations at high risk for invasion and impacts, respectively. We leverage a large aquatic vegetation dataset comprising point‐level survey data that includes information on the invasive plant Myriophyllum spicatum (Eurasian watermilfoil) to: (a) develop SDMs to predict invasion and impact from environmental variables based on presence–absence, presence‐only, and abundance data, and (b) compare evaluation metrics based on functional and discrimination accuracy for presence–absence and presence‐only SDMs.LocationMinnesota, USA.MethodsEurasian watermilfoil presence–absence and abundance information were gathered from 468 surveyed lakes, and 801 unsurveyed lakes were leveraged as pseudoabsences for presence‐only models. A Random Forest algorithm was used to model the distribution and abundance of Eurasian watermilfoil as a function of lake‐specific predictors, both with and without a spatial autocovariate. Occurrence‐based SDMs were evaluated using conventional discrimination accuracy metrics and functional accuracy metrics assessing correlation between predicted suitability and observed abundance.ResultsWater temperature degree days and maximum lake depth were two leading predictors influencing both invasion risk and abundance, but they were relatively less important for predicting abundance than other water quality measures. Road density was a strong predictor of Eurasian watermilfoil invasion risk but not abundance. Model evaluations highlighted significant differences: Presence–absence models had high functional accuracy despite low discrimination accuracy, whereas presence‐only models showed the opposite pattern.Main conclusionComplementing presence–absence data with abundance information offers a richer understanding of invasive Eurasian watermilfoil''s ecological niche and enables evaluation of the model''s functional accuracy. Conventional discrimination accuracy measures were misleading when models were developed using pseudoabsences. We thus caution against the overuse of presence‐only models and suggest directing more effort toward systematic monitoring programs that yield high‐quality data.     

Contribution à l'analyse des structures forestières 2. Caractérisation et analyse du toit de la végétation

Data used come from point-height analysis. 100 sample points are arranged in 4 lines of 25, with 24 m between lines and 1 m between points on lines. At each point, vertical lists of species are compiled, by measurement strata. Such strata depth is 10 cm when mean vegetation height in the stand is lower than 4–5 m and 50 cm when heigher. A synthetic vegetation profile is obtained by sum of species presences in each measurement stratum for all 100 observations. When these profiles are bimodal, vegetation can be divided in two at the secondary minimum level: the upper part is the canopy, the lower the understorey. Only the canopy structure is dealt with in this tudy. Several parameters, describing vertical structure of woody vegetation, are defined and measured. They are: (1) maximum height, (2) upper and lower canopy limits, (3) canopy depth and (4) density. Delimitation of canopy is achieved by calculating the hypegeometric probability of realisation groups of vegetation presence, or absence, in the vertical line of sight. The thickness is the difference between the two previous values (2) and (3) and density the number of intercepts between them. Horizontal variations in those structural parameters are revealed by cumulative sum method which demonstrates different types of pattern. Relations between horizontal variations are studied by pairs; actual values compared by linear correlation analysis while concordance between patterns are characterised by the coefficient of simple concordance ofSokal etMitchner and by a binary autocorrelation coefficient.Shannon's formula enables an overall appreciation of canopy homogeneity. an example is applied to some stands ofNothofagus antarctica (Forest) Verst. in Southern Chile and Argentina. The upper canopy limits are the same upper vegetation intercepts so canopies are smooth. High correlation exists between upper and lower limits of the canopies, and low correlation between the latter and thickness and density, so canopies are uniform.     

Synchronicity in elevation range shifts among small mammals and vegetation over the last century is stronger for omnivores

In mountain ecosystems, species can be said to respond synchronously to environmental change when the elevation ranges of vegetation types and their associated vertebrates expand or contract in the same direction. Conversely, the response is asynchronous when the elevation ranges of vegetation types and associated vertebrates change in different directions. The capacity of vertebrate species to respond synchronously with change in the elevation ranges of the vegetation that comprises their habitat is likely a function of their ecological traits. Here we combine measures of elevation range shifts in 23 vertebrate species with those of their associated vegetation types across 80 yr, on a large elevation transect in California's Sierra Nevada mountains that encompasses Yosemite National Park. Half the species’ shifts were synchronous with vegetation shifts, ¼ of the species were asynchronous, and the others showed no relationship. Most species that responded synchronously to changes in vegetation elevation ranges expanded their elevation range, and are inhabitants of low and intermediate elevations. In contrast, those species whose range shifts were asynchronous to associated vegetation shifts inhabit high elevations. These species experienced contraction in elevation range even while their associated vegetation types expanded. However, these species were responding synchronously to a subset of their associated vegetation types. Considering trait‐based predictors, omnivores were more synchronous than herbivores. Our results on synchronous and asynchronous elevation shifts with vegetation may permit more accurate modeling of future ranges for vertebrates in California's Sierra Nevada. The approach also offers a new method for use in assessment of vertebrate vulnerability in other mountain regions, and can be an important component of assessing their vulnerability to climate change.     

Relationship between land uses and diversity of dung beetles (Coleoptera: Scarabaeinae) in the southern Atlantic forest of Argentina: which are the key factors?

The loss of natural habitats is one of the main drivers of biodiversity decline. Anthropogenic land uses preserving biotic and abiotic conditions of the native ecosystem are more suitable to preserve the native biodiversity. In this study, we explored changes in species richness and composition in different land uses of the southern Atlantic forest, considering three independent factors: (1) canopy (presence–absence), (2) type of vegetation (native–exotic) and (3) livestock (presence–absence). We expected a gradient of response in the richness and composition of the native forest dung beetle community, from land uses preserving canopy and native vegetation to open land uses with exotic vegetation. Dung beetles were sampled in protected native forests and four land uses, using two potential food resources: human dung and carrion. The species richness and composition of each habitat, as well as differences in composition and the influence of factors over diversity, were then analyzed. As expected, our results showed that land uses preserving canopy and native vegetation maintain the dung beetle diversity of the native forest. Moreover, while the three factors analyzed influenced dung beetle diversity, canopy cover was the main driver of dung beetle diversity loss. The main conclusion of this study is that the conservation of canopy (either native or exotic) is determinant to preserve highly diverse dung beetle communities and subsequently, the ecological functions performed by this taxon. However, the ecophysiological mechanism behind the response of dung beetles to habitat disturbance is poorly understood.     

Integrating mechanistic and correlative niche models to unravel range‐limiting processes in a temperate amphibian

Insights into the causal mechanisms that limit species distributions are likely to improve our ability to anticipate species range shifts in response to climate change. For species with complex life histories, a mechanistic understanding of how climate affects different lifecycle stages may be crucial for making accurate forecasts. Here, we use mechanistic niche modeling (NicheMapR) to derive “proximate” (mechanistic) variables for tadpole, juvenile, and adult Rana temporaria. We modeled the hydroperiod, and maximum and minimum temperatures of shallow (30 cm) ponds, as well as activity windows for juveniles and adults. We then used those (“proximate”) variables in correlative ecological niche models (Maxent) to assess their role in limiting the species’ current distribution, and to investigate the potential effects of climate change on R. temporaria across Europe. We further compared the results with a model based on commonly used macroclimatic (“distal”) layers (i.e., bioclimatic layers from WorldClim). The maximum temperature of the warmest month (a macroclimatic variable) and maximum pond temperatures (a mechanistic variable) were the most important range‐limiting factors, and maximum temperature thresholds were consistent with the observed upper thermal limit of R. temporaria tadpoles. We found that range shift forecasts in central Europe are far more pessimistic when using distal macroclimatic variables, compared to projections based on proximate mechanistic variables. However, both approaches predicted extensive decreases in climatic suitability in southern Europe, which harbors a significant fraction of the species’ genetic diversity. We show how mechanistic modeling provides ways to depict gridded layers that directly reflect the microenvironments experienced by organisms at continental scales, and to reconstruct those predictors without extrapolation under novel future conditions. Furthermore, incorporating those predictors in correlative ecological niche models can help shed light on range‐limiting processes, and can have substantial impacts on predictions of climate‐induced range shifts.     

退化天坑倒石坡林下优势物种生态位特征

以典型的中度退化天坑——巴家陷塘天坑为例,对其倒石坡生态交错带森林群落优势种种群进行生态位特征分析,以期为喀斯特天坑的生物多样性保护及天坑地表区域植被的生态修复提供科学参考.结果表明:土壤养分铵态氮、速效钾、有效磷相较于土壤水分和温度对天坑物种分布影响最显著,解释量分别为37.4%、32.8%、29.3%.随着天坑倒石坡坡位(坑口-上坡位-中坡位-下坡位-坑底)的变化,其林下植物生活型由常绿旱生向常绿湿中生变化,草本种群生态位重叠程度较灌木种群更大.灌木植物密花荚蒾、小雀花和草本植物一把伞南星、荩草有较宽的生态幅和抗逆性,占据天坑林下灌草层的上层.随着土壤碱性不断加强,灌木植物长圆叶梾木和草本植物尼泊尔老鹳草、黄龙尾失去竞争力.巴家陷塘林下优势种的生态位特征与针阔混交林的冠层结构、林下灌草的生态策略、天坑独特的生境、优势物种的重要值等密切相关.     

Scale dependence of temperature as an abiotic driver of species' distributions

Aim Scale dependence of patterns and processes remains one of the major unresolved problems in ecology. The responses of ecosystems to environmental stressors are reported to be strongly scale dependent, but projections of the effects of climate change on species' distributions are still restricted to particular scales and knowledge about scale dependence is lacking. Here we propose that the scale dependence of those species' niche dimensions related to climate change is strongly related to the strength of climatic cross‐scale links. More specifically, we hypothesize that the strong cross‐scale links between micro‐ and macroclimatic conditions are related to high cross‐scale similarity (low scale dependence) of species' realized temperature niches and, thus, species' spatial distributions. Location This study covers seven orders of magnitude of spatial scale, ranging from local‐scale (below a metre) and regional‐scale (kilometre) investigations in central European wetland ecosystems to continental‐scale (thousands of kilometres) studies of species' distributions. Methods We combined data on the spatial occurrence of species (vegetation records at local and regional scales, digitized distribution maps at the continental scale) with information about the corresponding temperature regime of vascular plant species occurring in environmentally stable wetland ecosystems characterized by strong cross‐scale links between micro‐ and macroclimatic conditions. Results We observed high cross‐scale similarity of the characteristics of species temperature niches across seven orders of magnitude of spatial scale. However, the importance of temperature as an abiotic driver decreased nonlinearly with decreasing scale, suggesting greater importance of additional (biotic) drivers of species' occurrence at small spatial scales. Main conclusions We report high cross‐scale similarity of realized temperature niches for species inhabiting ecosystems where small‐scale environmental noise is low and cross‐scale links between micro‐ and macroclimatic conditions are strong. By highlighting a strong relationship between abiotic and biotic cross‐scale similarity, our results will help to improve niche‐based species distribution modelling, one of the major assessment tools for determining the ecological effects of climate change.