基于GWR模型的伊河流域土壤有机碳空间分布特征及影响因素分析

土壤有机碳作为陆地碳库主体,其分布特征及与驱动因素的空间关系对土壤碳周转过程有重大影响。通过野外调查、采样和室内分析,基于地理加权回归（GWR）模型结合9个环境和土壤变量,建模分析伊河流域土壤有机碳空间分布状况,以及影响其分布的主要因素。研究发现,流域表层土壤有机碳在3.37-38.34 g/kg之间,上、中、下游有机碳分布存在空间差异,其中上游差异最大,下游差异最小。相关分析表明,有机碳与土壤理化性质相关性显著,与年平均气温以外的环境因子相关性不显著。GWR模型较好地预测了伊河流域土壤有机碳空间分布,局部决定系数在0.49-0.64之间,自下游到上游,决定系数逐步升高,对上游的预测精度最高。分析发现,在海拔较高的中上游区域,土壤有机碳含量主要受立地环境、成土母质和地表覆盖的影响;在中上游低山丘陵区,人类活动和环境因素共同影响了土壤有机碳含量;在中下游平原区农业活动和化肥投入是造成土壤有机碳含量较高的主要因素。研究揭示了各因素对有机碳影响的空间分异特征,可为伊河流域土壤生态系统的合理发展和管理提供依据。     

A quantile‐slicing approach for sufficient dimension reduction with censored responses

Sufficient dimension reduction (SDR) that effectively reduces the predictor dimension in regression has been popular in high‐dimensional data analysis. Under the presence of censoring, however, most existing SDR methods suffer. In this article, we propose a new algorithm to perform SDR with censored responses based on the quantile‐slicing scheme recently proposed by Kim et al. First, we estimate the conditional quantile function of the true survival time via the censored kernel quantile regression (Shin et al.) and then slice the data based on the estimated censored regression quantiles instead of the responses. Both simulated and real data analysis demonstrate promising performance of the proposed method.     

基于多元回归树的公益林群落结构解析

为揭示不同生境类型下公益林群落物种多样性及优势种种间关系特征, 以临安市公益林125个固定监测样地为研究对象, 利用多元回归树(MRT)进行群落分类, 以物种多样性指数和种间联结系数为指标, 对不同群落类型的结构特征进行探索。结果表明: 临安市公益林125个典型样地可划分为5个类型; 类型I、II、III与类型V的多样性指数之间均无显著差异, 但类型III的多样性指数均最高, 类型IV的物种多样性指数均显著低于其它类型, 海拔是影响群落多样性水平的主要因子。种间联结初步分析显示, 研究区群落中稳定性最高的层片是乔木层, 且毛竹入侵极可能是影响5个类型植物群落稳定性的关键因素。研究结果可为临安市公益林分类经营管理提供理论依据, 同时为区域公益林群落数量结构研究奠定基础。     

北京城市公园湿地休憩功能的利用及其社会人口学因素

城市公园湿地是城市重要的生态基础设施,是城市居民休闲游憩的重要场所,具有重要的生态、社会文化服务功能。以北京地区20个典型的公园湿地为研究对象,采用问卷调查方法,将定性指标和定量指标相结合,用统计学方法分析了休憩者对公园湿地的使用情况,并采用Logistic回归方法揭示了影响城市公园湿地利用的社会人口学因素。结果表明:(1)休憩者到访公园湿地的距离与使用频率密切相关,43.4%的休憩者到达公园湿地的行程时间<1 h,这其中34.1%的休憩者使用公园湿地的频率每年在12次以上;仅有17.4%的休憩者每年使用各公园湿地频率为12次以上,这其中85%到达各公园湿地的行程时间<1h;(2)影响休憩者对公园湿地使用频率为每年12次以上的因素依次为行程时间、个人月收入、有无私家车、文化程度、职业、年龄。另外,性别与年龄的交互作用也有一定的影响;(3)愉悦身心是休憩者使用各公园湿地的最主要原因。研究旨在为城市公园湿地的合理优化与配置、城市绿地系统规划及城市的可持续发展提供科学依据。     

Structural features that predict real-value fluctuations of globular proteins

It is crucial to consider dynamics for understanding the biological function of proteins. We used a large number of molecular dynamics (MD) trajectories of nonhomologous proteins as references and examined static structural features of proteins that are most relevant to fluctuations. We examined correlation of individual structural features with fluctuations and further investigated effective combinations of features for predicting the real value of residue fluctuations using the support vector regression (SVR). It was found that some structural features have higher correlation than crystallographic B‐factors with fluctuations observed in MD trajectories. Moreover, SVR that uses combinations of static structural features showed accurate prediction of fluctuations with an average Pearson's correlation coefficient of 0.669 and a root mean square error of 1.04 Å. This correlation coefficient is higher than the one observed in predictions by the Gaussian network model (GNM). An advantage of the developed method over the GNMs is that the former predicts the real value of fluctuation. The results help improve our understanding of relationships between protein structure and fluctuation. Furthermore, the developed method provides a convienient practial way to predict fluctuations of proteins using easily computed static structural features of proteins. Proteins 2012; © 2012 Wiley Periodicals, Inc.     

我国林火发生预测模型研究进展

通过文献回顾,总结了国内林火发生预测模型的研究现状,并从林火发生驱动因子、林火发生概率预测模型、林火发生频次预测模型和模型检验方法等方面进行归纳分析。得出以下结论: 1)气象、地形、植被、可燃物、人类活动等因素是影响林火发生及模型预测精度的主要驱动因子;2)林火发生概率模型中,地理加权逻辑斯蒂回归模型考虑了变量之间的空间相关性,Gompit回归模型适宜非对称结构的林火数据,随机森林模型不需要多重共线性检验,在避免过度拟合的同时提高了预测精度,是林火发生概率预测模型的优选方法之一;3)林火发生频次模型中,负二项回归模型更适合对过度离散数据进行模拟,零膨胀模型和栅栏模型可以处理林火数据中包含大量零值的问题;4)ROC检验、AIC检验、似然比检验和Wald检验方法是林火概率和频次模型的常用检验方法。林火发生预测模型研究仍是我国当前林火管理工作的重点,预测模型的选择需要依据不同地区林火数据特点。此外,构建林火预测模型时需要考虑更多的影响因素,以提高模型预测精度;未来,需要进一步探索其他数学模型在林火发生预测中的应用,不断提高林火发生预测模型的准确度。     

Application of frequency ratio and logistic regression models for assessing physical wetland vulnerability in Punarbhaba river basin of Indo-Bangladesh

Growingly scarce ecologically viable flood plain wetland of the Punarbhaba river basin is further endangered due to flow modification through Komardanga dam. This work intends to discover physical vulnerability of the wetlands in Punarbhaba river basin of Indo-Bangladesh considering seven conditioning parameters, e.g., water presence frequency (WPF) map, flood inundation map, frequency of pixel being non-permanent, agriculture presence frequency (APF) map, fragmentation of wetland, normalized differentiation built up index (NDBI), and wetland changes (WC). Frequency Ratio and Logistic Regression models have been used for deriving the vulnerability of wetland for both pre (1988–1992) and post dam (1993–2016) periods. From computed FR models it is exhibited that out of the total wetland area (194.81 km²), 5.88% and 2.92% area are high and very highly vulnerable in pre-dam period but such vulnerable area is increased to 33.45% and 23.10% in post-dam state (total wetland: 126.11 km²). LR models also state that in pre-dam period, high and very high vulnerable wetland area were 5.02% and 3.82% (total wetland: 194.79 km²) and it is enhanced to 28.94% and 24.49% in post-dam state (total wetland: 126.11 km²). Extensions of agricultural land, squeezing of active flood plain, lowering flood frequency are dominant determinants for growing wetland vulnerability.     

胚乳性状数量基因的定位方法

将三倍体胚乳性状的数量遗传模型和二倍体性状数量基因（QTL）图构建方法相结合,导出双侧标记基因型下有关胚乳性状QTL的遗传组成、平均数和遗传方差分量,据之提出以某一区间双侧标记基因型胚乳性状的平均值为依变数,以该区间内任一点假定存在的QTL的加性效应d、显性效应h1和／或h2的系数为自变数,进行有重复观察值的多元线性回归分析,根据多元线性回归的显著性测验该点是否存在QTL,并估计出QTL的遗传效应。给定区间内任一点,皆可以此进行分析,从而可在整条染色体上作图,并以之确定QTL的数目和最可能位置,同时,在检测某一区间时,利用多元线性回归方法将该区间外可能存在的QTL的干扰进行统计控制,以提高QTL检测的精度。此外,还讨论了如何将之推广应用于其他类型的DNA不对应资料以及具复杂遗传模型的胚乳性状资料。     

Predicting patch occupancy in fragmented landscapes at the rangewide scale for an endangered species: an example of an American warbler

AIM: Our objective was to identify the distribution of the endangered golden-cheeked warbler (Setophaga chrysoparia) in fragmented oak-juniper woodlands by applying a geoadditive semiparametric occupancy model to better assist decision-makers in identifying suitable habitat across the species breeding range on which conservation or mitigation activities can be focused and thus prioritize management and conservation planning. LOCATION: Texas, USA. METHODS: We used repeated double-observer detection/non-detection surveys of randomly selected (n = 287) patches of potential habitat to evaluate warbler patch-scale presence across the species breeding range. We used a geoadditive semiparametric occupancy model with remotely sensed habitat metrics (patch size and landscape composition) to predict patch-scale occupancy of golden-cheeked warblers in the fragmented oak-juniper woodlands of central Texas, USA. RESULTS: Our spatially explicit model indicated that golden-cheeked warbler patch occupancy declined from south to north within the breeding range concomitant with reductions in the availability of large habitat patches. We found that 59% of woodland patches, primarily in the northern and central portions of the warbler's range, were predicted to have occupancy probabilities ≤0.10 with only 3% of patches predicted to have occupancy probabilities >0.90. Our model exhibited high prediction accuracy (area under curve = 0.91) when validated using independently collected warbler occurrence data. MAIN CONCLUSIONS: We have identified a distinct spatial occurrence gradient for golden-cheeked warblers as well as a relationship between two measurable landscape characteristics. Because habitat-occupancy relationships were key drivers of our model, our results can be used to identify potential areas where conservation actions supporting habitat mitigation can occur and identify areas where conservation of future potential habitat is possible. Additionally, our results can be used to focus resources on maintenance and creation of patches that are more likely to harbour viable local warbler populations.