共查询到18条相似文献，搜索用时 46 毫秒
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Meta分析中几种常用效应值的介绍 总被引：3，自引：0，他引：3
效应值是定量Meta分析中的结合统计量,其计算方法主要依赖于对原文献数据的获取程度,介绍并比较适合3种原文献数据报道形式的几种效应值的计算方法。 相似文献
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Meta分析中几种常用效应值的介绍 总被引：1，自引：0，他引：1
效应值是定量Meta分析中的结合统计量,其计算方法主要依赖于对原文献数据的获取程度,介绍并比较适合3种原文献数据报道形式的几种效应值的计算方法。 相似文献
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效应值是定量Meta分析中的结合统计量,其计算方法主要依赖于对原文献数据的获取程度,介绍并比较适合3种原文献数据报道形式的几种效应值的计算方法。 相似文献
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生态学整合分析中两种常用效应值的实例应用比较 总被引：4，自引：0，他引：4
整合分析(meta-analysis)是对同一主题下多个独立实验结果进行综合的统计学方法,被认为是到目前为止最好的数量综合方法,其统计量为效应值,反应比(InR)和Hedges'd值是生态学应用中最常用的两个效应值。以综合植物生理生态学指标对大气CO2浓度倍增响应为实例,比较这两种效应值的不同之处。采用两种效应值指标会对同一个生理生态指标产生不同的总效应值大小,有时甚至会改变效应值的方向;InR相对Hedges'd更易产生正效应值;Hedges'd较InR可拉大不同生理生态指标之间总效应值的差异;Hedges'd具有正负效应对称性,而InR却具有正负效应的不对称性。 相似文献
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效应值是定量Meta分析中的结合统计量,其计算方法主要依赖于对原文献数据的获取程度,介绍并比较适合3种原文献数据报道形式的几种效应值的计算方法。 相似文献
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整合分析中两种假设模型的介绍及实例分析* 总被引：5，自引：1，他引：4
整合分析(meta-analysis)是对同一主题下多个独立实验结果进行综合的统计学方法,被认为是到目前为止最好的数量综合方法。在进行整合分析时,首选应提出统计假设,根据假设的不同可将整合分析分为固定效应模型(fixedeffect model)和随机效应模型(random effect model),前者假定有相似的多个研究在同一分组里有一个共同的真实效应值,由于取样误差,导致在实际效应值的测定中各研究间存在差别;在后者中,假定各研究间有随机变量,因此,不共享一个真实效应值。介绍了两种假设模型下整合分析的计算方法,并进行了实例分析。 相似文献
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铁效应元件结合蛋白２的特性李昕权,郑敏（华西医科大学附属二院血液研究室,成都６１００４１）关键词铁效应元件结合蛋白２铁效应元件结合蛋白（ｉｒｏｎｒｅｓｐｏｎｓｉｖｅｅｌｅｍｅｎｔｂｉｎｄｉｎｇｐｒｏｔｅｉｎ,ＩＲＥ－ＢＰ）在细胞内铁代谢平衡的转录后调... 相似文献
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土地覆盖及其变化研究一直是全球变化研究的焦点,而土地覆盖作为生态系统的重要组成成分,具有明显的空间尺度（包括空间粒度和幅度）属性,不仅如此,尺度问题还成为景观空间研究的关键环节之一.因此,研究了解土地覆盖的尺度效应具有重要的理论意义与实际意义.基于高分辨率SPOT遥感数据,对广州市土地覆盖的景观特征进行类型及景观水平的粒度效应研究.结果表明,粒度增加对优势的景观类型有加强作用;粒度效应在类型和景观水平上都存在“临界阈”现象,粒度10、32和128是“临界阈”粒度.不同土地覆盖类型、不同特征指数的粒度响应存在差异：绿地和水域是对粒度响应最敏感的两种土地覆盖类型,而园地的斑块密度和面积百分比对粒度变化不敏感.景观水平上,斑块密度和平均形状指数的粒度响应最强烈,多样性指数则最弱,反映不同粒度形成的景观的异质性不同. 相似文献
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Aims Soil heterogeneity is ubiquitous in many ecosystems. We hypothesized that plant communities with higher species richness might be better adapted to soil heterogeneity and produce more biomass than those with lower richness. This is because there is niche differentiation among species and different species can complement each other and occupy a broader range of niches when plant species richness is high. However, no study has tested how soil particle heterogeneity affects the yield of plant communities, and whether such effects depend on the spatial scale of the heterogeneity and the species richness within the communities.Methods In a greenhouse experiment, we sowed seeds of four-species or eight-species mixtures in three heterogeneous treatments consisting of 32, 8 or 2 patches of both small (1.5mm) and large quartz (3.0mm) particles arranged in a chessboard manner and one homogeneous treatment with an even mixture of small and large quartz particles.Important findings Biomass production was significantly greater in the communities with high species richness than those with low species richness. However, soil particle heterogeneity or its interactions with patch scale or species richness did not significantly affect biomass production of the experimental communities. This work indicates that plant species richness may have a bigger impact on plant productivity than soil particle heterogeneity. Further studies should consider multiple sets of plant species during longer time periods to unravel the potential mechanisms of soil heterogeneity and its interactions with the impacts of species richness on community yield and species coexistence. 相似文献
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Yongjie Liu Chunyan Ma Shiting Liu Mingrui Liu Hui Li Mingxia Wang Guoe Li Hans J. De Boeck Fujiang Hou Zhanhui Tang Zhenxin Li 《Journal of Plant Ecology》2024,17(4):0
中心植物在异质土壤中生长时会受到邻体植物的显著影响。先前关于禾本科植物的研究表明,土壤异质性和物种组成会影响植物生物量和地上-地下生物量的分配。本研究旨在探究在非禾本科草本植物中是否也有类似的结果。本研究将3种非禾本科草本植物(即大米草Spartina anglica、二色补血草Limonium bicolor和碱蓬Suaeda glauca)分别种植在3个水平的土壤异质性处理中。通过将资源丰富基质和资源贫瘠基质相间填充到小斑块、中斑块或大斑块中得到不同的土壤异质性处理;通过将上述3种目标植物单一栽培、两两混和栽培以及3种混合栽培种植得到不同的物种组成处理。研究结果表明,斑块大小和物种组成的交互作用显著影响植株生物量、根系生物量、总生物量,而且这种结果体现在不同的研究尺度上。具体而言,在花盆尺度上,植株生物量、根系生物量和总生物量随着斑块大小的增加而增加。在基质尺度上,无论是在资源丰富基质还是资源贫瘠基质中,大斑块中的植株生物量和总生物量都高于中等斑块。最后,在群落尺度上,单一栽培比两两混合栽培或3种混合栽培具有更高的植株生物量、根系生物量和总生物量。上述结果与先前关于禾本科植物的研究结果不同,即禾本科植物植株生物量和总生物量随着斑块大小的增加而减少,并且资源丰富基质的植株生物量和总生物总量高于资源贫瘠基质。为了进一步阐明土壤异质性对邻体植物间相互作用的影响,我们建议对包含多功能群植物在内的植物群落开展长期的实验研究。 相似文献
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Julia Bebout;Jeremy W. Fox; 《Oikos》2024,2024(6):e10722
Ecological meta-analyses usually exhibit high relative heterogeneity of effect size: most among-study variation in effect size represents true variation in mean effect size, rather than sampling error. This heterogeneity arises from both methodological and ecological sources. Methodological heterogeneity is a nuisance that complicates the interpretation of data syntheses. One way to reduce methodological heterogeneity is via coordinated distributed experiments, in which investigators conduct the same experiment at different sites, using the same methods. We tested whether coordinated distributed experiments in ecology exhibit 1) low heterogeneity in effect size, and 2) lower heterogeneity than meta-analyses, using data on 17 effects from eight coordinated distributed experiments, and 406 meta-analyses. Consistent with our expectations, among-site heterogeneity typically comprised <50% of the variance in effect size in distributed experiments. In contrast, heterogeneity within and among studies typically comprised >90% of the variance in effect size in meta-analyses. However, this difference largely reflected the small size of most coordinated distributed experiments, and was no longer significant after controlling for size (number of studies or sites). These results are consistent with the hypothesis that methodological heterogeneity rarely comprises a substantial fraction of variance in effect size in ecology. We also conducted pairwise comparisons of absolute heterogeneity between coordinated distributed experiments and meta-analyses on the same topics. Coordinated distributed experiments did not consistently exhibit lower absolute heterogeneity in effect size than meta-analyses on the same topics. Our findings suggest that coordinated distributed experiments rarely increase uniformity of results by reducing methodological heterogeneity. Our results help refine the numerous distinct reasons for conducting coordinated distributed experiments. 相似文献
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The degree to which plant communities are vulnerable to invasion by alien species has often been assessed using the relationship between native and alien plant species richness (NAR). Variation in the direction and strength of the NAR tends to be negative for small plot sizes and study extents, but positive for large plots and extents. This invasion paradox has been attributed to different processes driving species richness at different spatial scales. However, the focus on plot size has drawn attention away from other factors influencing the NAR, in part because the influence of other factors may be obscured by or interact with plot size. Here, we test whether variation in the NAR can be explained by covariates linked to community susceptibility to invasion and whether these interact with plot size using a quantitative meta‐analysis drawn from 87 field studies that examined 161 NARs. While plot size explained most variation, the NAR was less positive in grassland habitats and in the Australasian region. Other covariates did not show strong relationships with the NAR even after accounting for interactions with plot size. Instead, much of the unexplained variation is associated with article or author specific differences, suggesting the NAR depends strongly on how different authors choose their study system or study design. 相似文献
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Mapping and assessment of ecosystem services in agricultural landscapes as required by the EU biodiversity policy need a better characterization of the given landscape typology according to its ecological and cultural values. Such need should be accommodated by a better discrimination of the landscape characteristics linked to the capacity of providing ecosystem services and socio-cultural benefits. Often, these key variables depend on the degree of farmland heterogeneity and landscape patterns. We employed segmentation and landscape metrics (edge density and image texture respectively), derived from a pan-European multi-temporal and multi-spectral remote sensing dataset, to generate a consistent European indicator of farmland heterogeneity, the Farmland Heterogeneity Indicator (FHI). We mapped five degrees of FHI on a wall-to-wall basis (250 m spatial resolution) over European agricultural landscapes including natural grasslands. Image texture led to a clear improvement of the indicator compared to the pure application of Edge Density, in particular to a better detection of small patches. In addition to deriving a qualitative indicator we attributed an approximate patch size to each class, allowing an indicative assessment of European field sizes. Based on CORINE land cover, we identified pastures and heterogeneous land cover classes as classes with the highest degree of FHI, while agroforestry and olive groves appeared less heterogeneous on average. We performed a verification based on a continental and regional scale, which resulted in general good agreement with independently derived data. 相似文献
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A meta-analysis was conducted on 136 data sets of denitrification rates (DR) recorded both during the period of highest water temperature and monthly in five types of aquatic ecosystems: oceans, coastal environments, estuaries, lakes and rivers. There was a gradual increase of DR from the ocean to rivers and lakes at both scales, with the rivers showing the highest DR variability. Denitrification peaked during summertime and showed highest seasonal variability in lakes and rivers. High concentrations of nitrate and interstitially-dissolved organic carbon as well as low oxygen concentration in the overlying water enhanced DR both during summer and at a seasonal scale whereas total phosphorus did at the seasonal scale only. There was a positive linear relationship between overlying nitrate and DR over the range of 1–970 μmol NO3 (r 2 = 0.86, P = 0.001). DR in lakes and rivers might reach values doubling those in the more denitrifying terrestrial ecosystems (e.g. agrosystems). Discrepancies in DR and its controlling factors between site-specific studies and this meta-analysis may arise from environmental variability at two, often confounded, scales of observation: the habitat and the ecosystem level. Future studies on denitrification in aquatic environments should address the topic of spatial heterogeneity more thoroughly. 相似文献