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1.
Species richness and evenness are the two major components of biodiversity, but the way in which they are interrelated is a subject of contention. We found a negative relationship between the two variables for bird communities at 92 woodland sites across Australia and sought an explanation. Actual evapotranspiration (AET) was by far the best predictor of species richness. When AET was controlled for, the relationship between richness and evenness became nonsignificant. Richness is greater at sites with higher AET because such sites support a greater number of individuals. However, such sites have a greater number of rare species, resulting in lower evenness. A complicating factor is that evenness is best predicted by degree of vegetation cover, with sparsely vegetated sites having significantly lower evenness. We conclude that there are two competing ecological processes, related to energy and water availability, that determine richness and evenness. The first drives total abundance (leading to high richness, low evenness), while the second drives productivity and niche availability (leading to high richness, high evenness). The relative strength of these two processes and the observed relationship between richness and evenness are likely to depend on the scale of the analysis and the species and range of habitats studied.  相似文献   

2.
张敬怀 《生物多样性》2014,22(3):302-1263
利用2006年7-8月(夏季)、2007年4-5月(春季)和2007年10-12月(秋季)珠江丰水期、平水期和枯水期3个航次在南中国海北部珠江口附近海域4条由河口、近岸到深水区调查断面的数据, 研究大型底栖动物多样性由河口-近岸-深水的变化趋势及与环境因子的关系。春季、夏季和秋季分别获得大型底栖动物273、256和148种, 各季节均以环节动物种类最多, 节肢动物次之。大型底栖动物种类数、丰度、生物量和Shannon-Wiener多样性指数均由河口向近岸海域升高, 再由近岸向外海深水区降低。Pielou均匀度深水区最高, 其次为近岸。河口和深水区大型底栖动物k-优势度曲线位于近岸浅水域曲线之上, 表明生物多样性由河口向近岸升高, 而由近岸向深水则降低。大型底栖动物与环境因子Pearson相关性分析表明, 春、秋季大型底栖动物种类数、丰度和生物量与水深呈显著的负相关, 秋季种类多样性指数和均匀度也与水深呈显著的负相关性, 而夏季仅生物量与水深呈显著的负相关; 春、秋季大型底栖动物种类数、生物量、丰度、多样性指数和种类均匀度与盐度的相关性不显著, 但是夏季大型底栖动物种类数、丰度、多样性指数和种类均匀度与盐度呈显著正相关。单位面积(0.2 m2)内, 珠江口及邻近海域大型底栖动物在近岸浅水区较深水区和河口生物多样性高, 且生物量丰富。  相似文献   

3.
Maohua Ma 《应用植被学》2008,11(2):269-278
Question: How does agricultural land usage affect plant species diversity in semi‐natural buffer strips at multiple scales? Location: Lepsämä River watershed, Nurmijärvi, Southern Finland. Methods: Species diversity indicators included both richness and evenness. Plant communities in buffer strips were surveyed in 29 sampling sites. Using ArcGIS Desktop 9.0 (ArcInfo) and Fragstats 3.3 for GIS analysis, the landscape composition around each sampling site was characterized by seven parameters in square sectors at five scales: 4, 36, 100, 196, and 324ha. For each scale, Principle Component Analysis was used to examine the importance of each structural metric to diversity indicators using multiple regression and other simple analyses. Results: For all but the smallest scales (4 ha), two structural metrics including the diversity of land cover types and percentage of arable land were positively and negatively correlated with species richness, respectively. Both metrics had the highest correlation coefficients for species richness at the second largest scale (196 ha). The density of arable field edges between the fields was the only metric that correlated with species evenness for all scales, which had highest predictive power at the second smallest scale (36 ha). Conclusions: Species richness and evenness of buffer strips had scale‐dependent relationships to land use in agricultural ecosystems. The results of this study indicated that species richness depends on the pattern of arable land use at large scales, which may relate to the regional species pool. Meanwhile, species evenness depended on the level of field edge density at small scales, which relates to how the nearby farmland was divided by the edges (e.g. many small‐scale fields with high edge density or a few big‐scale fields with low edge density). This implies that it is important to manage the biodiversity of buffer strips within a landscape context at multiple scales.  相似文献   

4.
This paper reports a study on species richness and composition of Tumbesian dry forest communities. We tested two alternative hypotheses about species assemblage processes in tropical dry forests: (1) species assemblage is determined by the filtering effect of environmental conditions and (2) species assemblage is determined by facilitative processes along the gradient of water availability, and thus, species richness and evenness increase as water becomes limited. In addition, we also explored the effect of climate and soil conditions on species composition in tropical dry forests. Species composition was sampled in 109 plots in terms of cover and tree diameter at breast height. Climatic, edaphic, topographic and anthropogenic degradation variables were obtained for each plot. We used generalized linear models and canonical correspondence analyses to evaluate the effect of environmental variables on species composition, richness and evenness. Water availability negatively affected richness and significantly determined the species assemblage. Species richness increased from ridges to valleys and evenness increased at higher altitudes. Soil characteristics showed no effect on richness and evenness but soil moisture, nitrogen concentration and soil temperature explained significant fractions of species composition. Although timber extraction and livestock in our study area were of low intensity, it negatively affected richness but had only a minor effect on species composition. Our results suggest that species composition in these endangered tropical dry forests may be at least partially explained by the stress‐gradient hypothesis, with higher species richness at drier conditions probably induced by facilitation processes.  相似文献   

5.
Ye M S  Guan W B  Wu B  Ma K M  Liu G H  Wang X L  Chen Q Y 《农业工程》2006,26(10):3159-3165
Biocomplexity theory is becoming increasingly important in understanding natural vegetation dynamics and interrelation among all components of the ecosystem. In this study, based on the field investigation of plant species and environmental factors (altitude, microtopography, soil water content, and soil nutrients) in an arid valley of the upper reaches of Minjiang River, Sichuan Province, southwestern China, plant community complexity and its relationship with environmental factors, community diversity, species evenness and richness were studied. Both total and structural complexities of the communities showed a “high- low-high” tendency with the increase in altitude of the area, which meant that the complexity of communities was the highest at the sites of low and high altitude, whereas it was the lowest at the sites of intermediate altitude. It was found that the total community complexity had significant quadratic correlations with soil organic matter (SOM) content, total nitrogen (N), hydrolyzable N, soil water content, and available potassium (K), whereas it had no significant correlations with soil total K, total phosphorus (P), available P, and pH value. The total community complexity positively correlated with community diversity, species evenness and species richness, whereas the structural complexity negatively correlated with the community evenness. Of the two components of the total community complexity, namely, the structural complexity and the structural diversity, the structural complexity was more sensitive than the structural diversity to the changes of species in the community, which was not only related to the community evenness but also to the community richness. The relative contribution of both the structural complexity and the structural diversity to the total complexity would be different for different study areas or ecosystems.  相似文献   

6.
Ecological restoration is increasingly applied in tropical forests to mitigate biodiversity loss and recover ecosystem functions. In restoration ecology, functional richness, rather than species richness, often determines community assembly, and measures of functional diversity provide a mechanistic link between diversity and ecological functioning of restored habitat. Vertebrate animals are important for ecosystem functioning. Here, we examine the functional diversity of small‐to‐medium sized mammals to evaluate the diversity and functional recovery of tropical rainforest. We assess how mammal species diversity and composition and functional diversity and composition, vary along a restoration chronosequence from degraded pasture to “old‐growth” tropical rainforest in the Wet Tropics of Australia. Species richness, diversity, evenness, and abundance did not vary, but total mammal biomass and mean species body mass increased with restoration age. Species composition in restoration forests converged on the composition of old‐growth rainforest and diverged from pasture with increasing restoration age. Functional metrics provided a clearer pattern of recovery than traditional species metrics, with most functional metrics significantly increasing with restoration age when taxonomic‐based metrics did not. Functional evenness and dispersion increased significantly with restoration age, suggesting that niche complementarity enhances species' abundances in restored sites. The change in community composition represented a functional shift from invasive, herbivorous, terrestrial habitat generalists and open environment specialists in pasture and young restoration sites, to predominantly endemic, folivorous, arboreal, and fossorial forest species in older restoration sites. This shift has positive implications for conservation and demonstrates the potential of tropical forest restoration to recover rainforest‐like, diverse faunal communities.  相似文献   

7.
广西马尾松林植物功能多样性与生产力的关系   总被引:1,自引:0,他引:1  
探索植物多样性与生产力的关系可为森林经营与管理提供科学基础。本研究以广西4个地区的马尾松(Pinus massoniana)人工林群落为研究对象, 通过计算物种多样性、功能多样性和功能优势值, 运用相关分析、自动线性建模和方差划分等方法, 分析了多样性与生产力的关系。研究发现, 生产力与物种丰富度、Shannon指数、功能丰富度、功能均匀度极显著正相关(P < 0.01), 与物种均匀度、功能多样性、功能离散度、功能团个数、坡向显著正相关(P < 0.05), 与林龄极显著负相关(P < 0.01), 4个功能多样性参数和4个物种多样性参数两两之间皆为显著正相关; 未发现初始生物量制约生产力的提高; 方差划分最优模型中, 功能多样性参数效应、功能优势值效应和林龄效应分别解释生产力方差的56%、43%和33%, 功能多样性参数效应和功能优势值效应重叠部分高达27%; 生态位互补效应主要由功能丰富度和功能均匀度产生, 选择效应主要由生长型优势值产生; 生长型优势值为灌木的样地生产力较高, 次优种或过渡种对生态系统功能也有重要作用。以生产力为响应变量的自动线性建模最佳子集包括重要性由大到小的5个因素: 林龄、生长型优势值、功能丰富度、功能均匀度、功能团个数。建议维护森林功能多样性, 加强林下叶层植物保护, 用好功能重要的物种, 通过林下叶层的补偿性光合作用和生长竞争, 有效地提高生产力和生物多样性。  相似文献   

8.
《Acta Oecologica》2002,23(6):361-374
Oribatid mite and Carabid beetle communities were investigated at five sites in the ‘Pietraporciana’ and ‘Lucciolabella’ Nature Reserves (central Italy). In this part of southern Tuscany many attempts have been made to encourage the regeneration of native habitats and to preserve existing ones. Human-induced changes in the original forest landscape have had a direct impact on mite and carabid populations. Significant differences in species diversity and abundance among different sites were revealed throughout the sampling period. Species richness, abundance and diversity of oribatid mites decrease from woodland sites to open habitats where evenness was high. There is an inverse trend between the number of species and richness of carabid beetles and those of oribatid mites. Canonical correspondence analysis (CCA) of oribatid and carabid beetle compositions discriminated the sites, demonstrating how even small areas with different vegetation, composition, structure, environment and microclimate were characterised by distinct edaphic populations.  相似文献   

9.
The proliferation of non-native species in North American freshwater ecosystems is considered a primary threat to the integrity of native community structure. However, a general understanding of consistent and predictable impacts of non-native species on native freshwater diversity is limited, in part, because of a lack of broad-scale studies including data from numerous localities across multiple drainages. This study uses data from 751 localities collected during the United States Geological Survey (USGS) National Water Quality Assessment (NAWQA) program to examine the influence of non-native fish species on native freshwater fish assemblages across the United States. In general, no significant differences in native fish richness and diversity measures were detected between sites with only native species and sites containing non-native species. However, at sites with non-native species, the number of non-native species present was negatively correlated with native species richness and Shannon diversity and positively correlated with native evenness. Non-native piscivores were negatively correlated with native species richness and Shannon diversity and positively correlated with native evenness. Native piscivores were positively correlated with native richness and diversity and negatively correlated with native evenness at sites with only native species. Our results suggest that from a superficial perspective, native species richness and diversity are not different among sites with and without non-native species. However, when patterns of native species richness and diversity are examined at sites containing non-native species, correlations between non-native and native species richness and diversity imply the expected negative effect of invasive taxa. Additionally, non-native piscivores appear to have a significant negative effect on native taxa and possibly represent a novel selective force on naive native prey.  相似文献   

10.
The relationship between grass species richness and ecosystem stability was investigated in the Kruger National Park. A total of 135 489 individual grasses were identified from 189 sites spread across 19 485 km2 of savanna biome, making this one of the largest studies of its kind. At each site, grass percentage abundance and standing crop were measured at one year intervals to provide an index of ecosystem function. A severe drought that affected the region between 1991 and 1993 provided a convenient perturbation. At the height of the drought, mean species richness declined by 12.7% while standing crop declined by 38.1%, from 3199 to 1979 kg ha?1. Percentage grass abundance declined to 87.5% of its pre‐drought value. After the drought had passed species richness, standing crop and percentage abundance recovered to 92.1%, 113.8% and 92.8% of their pre‐perturbation values, respectively. Statistical analysis of these responses revealed that grass assemblages of low species richness were more resistant to drought than assemblages of high species richness. Species‐poor sites also showed better recovery from perturbation after the drought had passed. These findings suggest that ecosystem stability may be negatively related to grass species richness in South African savanna grasslands.  相似文献   

11.
Mountainous areas of the Korean Peninsula are among the biodiversity hotspots of the world's temperate forests. Understanding patterns in spatial distribution of their species richness requires explicit consideration of different environmental drivers and their effects on functionally differing components. In this study, we assess the impact of both geographical and soil variables on the fine-scale (400 m2) pattern of plant diversity using field data from six national parks, spanning a 1300 m altitudinal gradient. Species richness and the slopes of species–area curves were calculated separately for the tree, shrub and herb layer and used as response variables in regression tree analyses. A cluster analysis distinguished three dominant forest communities with specific patterns in the diversity–environment relationship. The most widespread middle-altitude oak forests had the highest tree richness but the lowest richness of herbaceous plants due to a dense bamboo understory. Total richness was positively associated with soil reaction and negatively associated with soluble phosphorus and solar radiation (site dryness). Tree richness was associated mainly with soil factors, although trees are frequently assumed to be controlled mainly by factors with large-scale impact. A U-shaped relationship was found between herbaceous plant richness and altitude, caused by a distribution pattern of dwarf bamboo in understory. No correlation between the degree of canopy openness and herb layer richness was detected. Slopes of the species–area curves indicated the various origins of forest communities. Variable diversity–environment responses in different layers and communities reinforce the necessity of context-dependent differentiation for the assessment of impacts of climate and land-use changes in these diverse but intensively exploited regions.  相似文献   

12.
在青藏高原进行了大范围的群落调查 ,研究高原的两种主要草地群落类型———高寒草甸和高寒草原的植物物种丰富度及其变化。结果表明 :(1)在 5 0个样地 2 5 0个 1m× 1m的样方中 ,共出现 2 6 7种植物 ,其中高寒草甸179种 ,高寒草原 135种。在高寒草甸 ,1m2 样方内物种数最多为 32种 ,最少的仅为 3种 ;在高寒草原 ,物种数最多为 18种 /m2 ,最少的仅为 2种 /m2 。 (2 )物种丰富度随经度和纬度的增加呈增加趋势 ;随海拔的上升呈减少趋势。对物种丰富度与环境因子之间进行逐步回归 ,发现物种丰富度与生长季降水和温暖指数呈显著正相关。 (3)物种丰富度与地上生物量呈显著正相关。  相似文献   

13.
We investigated the relationship between diversity and ecosystem function, which is controversial and has rarely been examined for consumer assemblages, for the process of leaf breakdown by the shredder guild in a tropical stream. We manipulated species richness, evenness and identity of four macroinvertebrate shredder species (three caddisflies and one mayfly) in microcosms and tested their effect on leaf breakdown rates measured as leaf mass loss per capita and per milligram of animal. Species richness, evenness and species identity all affected leaf breakdown rates. Breakdown rates tended to increase with higher richness, but only for the three caddisflies, probably through a release of intraspecific interference, although other mechanisms such as niche complementarity or facilitation cannot be discarded. Leaf breakdown by the caddisflies was reduced in the presence of the mayfly, possibly because of its mode of movement by swimming instead of crawling and its similarity to some predators that are common in leaf litter. Species identity was more important than species richness in determining leaf breakdown rates, indicating that some species within the shredder guild are not redundant, and suggesting important consequences of particular species loss for the functioning of the ecosystem.  相似文献   

14.
Abstract. Effects of grazing and environment on vegetation structure have been widely acknowledged, but few studies have related both factors. We made 57 floristic samples in a highly variable landscape of mountain grasslands in central Argentina; 26 sample were in fence‐lines with contrasting vegetation. For each sample, we recorded topographic and edaphic parameters, as well as grazing intensity indicators. Floristic gradients were analysed with DCA and relations with abiotic and grazing‐related variables were detected with DCCA. Floristic axis 1 was explained by edaphic parameters associated to topography, ranging from communities in well drained soils on upper topographic positions to hydromorphic vegetation in poorly drained soils on lower topographic positions. Species richness decreased as soil moisture increased. Floristic axis 2 was associated with present and long‐term grazing indicators, and reflected shifts in vegetation physiognomy and species evenness. Tall tussock grasslands, with low species evenness and evidences of low or null grazing intensity were located at one extreme. Tussocks were gradually replaced by short graminoids and forbs towards the centre of the gradient, as grazing increased, and evenness reached a maximum. In degraded sites with heavy long‐term grazing intensities, short perennial species were replaced by an annual species, and evenness decreased. The magnitude of changes in floristic composition produced by grazing decreased with increasing soil moisture, and vegetation‐environment relationships were stronger in moderate to highly grazed situations than in lightly or non grazed situations.  相似文献   

15.
Evenness is an important property of communities. Species richness alone does not capture the fact that one or a few species may dominate total abundance and biomass of a community. This in turn has important consequences for ecosystem functioning and species interactions. Evenness has been observed to vary systematically along environmental and productivity gradients. However, a truly general theory about which factors control evenness in a community has yet to emerge. Prior research on evenness has suggested that high richness, biomass and abundance should lead to lower community evenness in our study system of bats in Panama. However, only few empirical studies examine the simultaneous effects of species richness, biomass or abundance on evenness. For the first time, we applied path analysis in the study of evenness to tease apart the relative importance and direction (positive or negative) of causality among these three factors. As predicted, we found that evenness decreases with increasing species richness, abundance and biomass. The negative effect of abundance was mediated by the positive joint effect of biomass and richness. The selected models varied in the strength of the correlation between the three variables with evenness but their direction was consistent. Overall, we argue that rarity, high mobility and differences in resource availability at sites with lower environmental stress can explain the negative effects of richness on evenness.  相似文献   

16.
2006年4月中旬至6月下旬, 采用典型取样法, 在三峡库区某磷化工厂周围污染源区与对照区设置样方, 进行常规群落学调查, 分析点源污染对陆生植物群落种类组成以及物种多样性的影响。结果表明: (1) 所有样方中共计出现284种植物, 其中乔木35种, 灌木139种, 草本110种。仅在污染区中出现的物种数量远低于仅在对照区中出现的物种数量; (2) 可分出4种基本的群落类型: 马尾松(Pinus massoniana)林、柏木(Cupressus funepris)林、栓皮栎(Quercus variabilis)林和马尾松+栓皮栎林, 各群落特定层次的物种丰富度指数以及Pielou均匀度指数在污染区与对照区之间存在显著差异; (3)污染胁迫下, 物种在群落中的生态优势度发生了变化, 反映了群落中不同物种相互替代的过程, 这种物种的替代可为今后受损生态系统人为恢复过程中物种的筛选提供一定的理论参考; (4)对群落中主要物种更新的调查发现: 栓皮栎林对污染不敏感; 柏木林污染区与对照区幼苗数量及分布格局均有明显差异, 污染条件下群落未来演替受到严重干扰。综上所述, 我们可以看出, 在点源污染影响下, 群落的组成和结构发生了显著变化, 但这种变化对群落的长期影响仍需要进一步的深入研究。  相似文献   

17.
Richness, structure and functioning in metazoan parasite communities   总被引:4,自引:0,他引:4  
Ecosystem functioning, characterized by components such as productivity and stability, has been extensively linked with diversity in recent years, mainly in plant ecology. The aim of our study was thus to quantify general relationships between diversity, community structure and ecosystem functions in metazoan parasite communities. We used data on parasite communities from 15 species of marine fish hosts from coastal Chile. The volumetric abundance (volume of all parasite species per individual host, in mm3) was used as a surrogate for productivity. Species diversity was measured using both species richness and evenness, while community structure was estimated using the co‐occurrence indices V‐ratio, C‐score and a new C‐scores index standardized for the number of host replicates. After correcting for fish size, 47% of host species show no relationship, 13% show a hump shaped curve and 40% show positive monotonic relationships between productivity and parasite richness across all host individuals in a sample. We obtained a logarithmically decreasing relationship between evenness and productivity for all fish species, and propose a ‘dominance‐resistance’ hypothesis based on immunity to explain this pattern. The stability of the parasite community, measured as the coefficient of variation in productivity among individual hosts, was strongly and positively related to mean species richness across the 15 host species. The C‐scores index, based on the number of checkerboard units in the host‐parasite presence/absence matrix, increases linearly with mean productivity across the 15 host species, suggesting that parasite communities tend to be more structured when they are more productive. This is the likely reason why linear relationships between richness and productivity were not observed consistently in all fish species. Parasite communities provide some clear patterns for the diversity–ecosystem functioning debate in ecology, although other factors, such as the history of community assembly, may also influence these patterns.  相似文献   

18.
生物多样性与生态系统生产力之间的关系是当前生态学领域的热点问题。短花针茅(Stipa breviflora)草原是内蒙古荒漠草原的主要类型, 生态系统脆弱, 气候波动剧烈, 研究内蒙古短花针茅草原生物多样性与生产力的关系具有十分重要的意义。该研究在内蒙古短花针茅草原区设置了202个样地进行群落调查, 在干旱区及半干旱区两种资源供给下, 分析了物种丰富度、功能群丰富度与生产力的关系, 旨在解决两个科学问题: 1)物种多样性和功能群多样性中, 哪一种与生产力关系更为密切?2)资源供给对多样性和生产力关系的影响。结果表明: 1)物种丰富度、群落生产力与年降水量呈正相关关系, 而功能群丰富度与年降水量之间不存在显著相关性; 2)群落生产力随物种丰富度的增加而增加, 且两者间呈正线性关系, 功能群丰富度与生产力之间不存在显著相关关系; 3)资源供给会影响多样性与生产力之间的关系, 资源供给低时, 多样性对生产力贡献较低, 资源供给高时, 多样性对生产力的贡献较高。该研究丰富了多样性与生产力关系的研究, 同时, 考虑到植物功能性状的研究在近几年受到生态学家的重视, 且多数研究集中于小尺度的人工控制实验, 因此, 在大尺度自然生态系统中开展功能性状多样性与生态系统功能关系的研究将十分必要。  相似文献   

19.
Aims Human impacts on natural ecosystems induce changes in their functioning through alterations in species richness, composition and evenness of plant communities. Most litter diversity–decomposition processes studies have only manipulated species richness, ignoring the role of evenness. Here, results from a field litterbag experiment are presented to test whether changes in evenness of species distribution in litter mixtures affected the strength of the litter-species richness–decomposition relationship.Methods Ten herbaceous species abundant in Mediterranean grassland communities and representative of different genera and functional groups were used. Species richness was directly manipulated to produce litter mixtures of three and six plant species, as well as litter of each individual species used. Each level of species richness was replicated several times such that each repeat had a different species composition. Three- and six-species litter mixtures were also treated to vary in evenness (three levels). Decomposition rate was assessed by percentage dry weight loss over the 90 days of the experiment.Important findings Decomposition rate was positively related to the linear increase in litter-species richness and was affected by the composition of the litter-species mixture. Decomposition rates differed significantly between evenness treatments and moreover, the strength of the positive relationship between litter-species richness and decomposition rate decreased notably in the low-evenness treatment. The effects of evenness on decomposition rate, at different richness levels, were partially explained by the differences in the initial litter mixture's carbon-to-nitrogen ratio within them. This study reveals that short-term decomposition rate is positively affected by both components of Mediterranean grassland litter-species diversity.  相似文献   

20.
The ecological role of historical land use has rarely been explored in the context of grassland restoration. We conducted a 4‐year field experiment in a steppe and an old field in Inner Mongolia in northern China to examine the influence of historical land use and water availability on ecosystem restoration. Species richness, evenness, and plant cover were higher in the steppe than in the old field. The steppe was more temporally stable compared with the old field in terms of species richness, evenness, plant density, and cover. Water addition increased peak aboveground biomass, belowground net primary productivity, species richness, plant density, and cover in both the steppe and the old field. Water addition also enhanced the stability of ecosystems and the restoration of grassland. Our findings suggested that historical land use determines community structure and influences the process of grassland restoration. Converting grasslands to farmland in semiarid areas can cause the long‐term loss of biodiversity and instability of ecosystem with consequent impacts on ecosystem services. The amendment of limited resources is an effective practice to increase the success of ecosystem restoration.  相似文献   

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