森林种群径阶转移模型中转移概率的估算方法

基于统计分析理论和微分方程理论,给出了森林种群径阶转移模型中估算转移概率的方法：第一种是在有两次样地观测数据,不考虑林分环境因子等因素的条件下估算转移概率;第二种是在已知林分环境因子条件下,不需要对样地有两次观测数据来估算转移概率.实例验证结果表明,两种估算转移概率的方法具有计算简单和实用性强的特点,对森林经营与管理有一定的理论指导和实际应用价值.     

森林生态价值估算方法研究进展

森林生态效益的重要性日益显现,科学家和各国政府都在关注森林生态价值估算,促进了森林生态价值估算方法的日渐成熟。本文总结了近年来国内外森林生态价值的估算方法,将目前常用的估算方法分为市场类估算法、能值估算法、软件模型法3大类,同时分析了前2种常用方法中存在的替代法的合理性有待验证、忽略多重标准的森林管理策略、欠缺考虑周围影响因素、多种生态价值重复计算以及估算中欠缺考虑稀缺性的局限;其次,重点介绍了能较好解决以上问题的GUMBO、CITYgreen和Invest等软件的特点和优势;最后,在总结当前估算方法研究的基础上,提出中国森林生态估算工作未来的研究方向是深化对森林生态结构和功能关系的认识,提高国外估算方法的适用性,加强生态补偿工作对估算方法的反馈。     

黄土高原北部典型灌丛枝条生物量估算模型

于2015年8月末在陕西神木县六道沟小流域采集200个柠条和210个沙柳枝条,测定枝条的基径(D)、长度(H)、含水量(W₀)、鲜质量(W_F)和干质量(W),选用指数函数和异速生长方程建立了4种由枝条形态指标估算枝条生物量的简易模型,并对模型的拟合效果进行验证. 结果表明: 对于柠条和沙柳灌丛,基于D、H二者组合变量(D²H)的异速生长方程是估算枝条生物量的最优模型,该模型经线性转化后可以消除生物量数据的异方差性,且拟合效果最优,决定系数(R²)最大,平均误差(ME)、平均绝对误差(MAE)、总相对误差(TRE)、平均系统误差(MSE)和平均绝对百分误差(MPSE)整体上最小,基本满足生态学研究的精度要求.     

双列杂交分析估算遗传参数两种方法的比较

本文就遗传参数的估算,对双列杂交分析中应用最广的Griffing法和Hayman法作了比较。结果表明,Hayman法估算非加性方差的结果比Griffing法小(p-1)/P~2_5~2, 而估算加性方差和遗传方差的结果则分别比Griffing法大2(p-1)/P~2_s~2和(p-1)/P~2_s~2。另外,本文还就造成两种方法分析结果不同的原因作了讨论。     

大仓鼠种群繁殖参数的估算

西文根据大仓鼠自然种群雌体怀胎率,各种类型子宫斑率和幼鼠比率的季节变动规律,估算了1986年河北饶阳县大仓鼠种群的繁殖参数,其研究结果如下：在当年的繁殖季节,大仓鼠越冬雌鼠繁殖3胎次;4、5月份的幼鼠繁殖2胎次;6、7月份的幼鼠繁殖1胎次;9月份左右的幼鼠不参加繁殖。越冬雌鼠春季怀胎和产仔近似正态分布,分布标准差约为13天,平均值为4月20日。幼鼠成熟历期（幼雌体自产出至其产仔）为62天。生殖时滞（雌体两次繁殖间隔）为59天。平均胎仔数为9.1260±2.5971。雌雄性比为1∶1.4926。幼鼠上铗历期为24天。繁殖终止平均日期为9月20日。     

生物量精确估算模型与参数辨识方法及应用

从生物量模型的构建与参数辨识方法的改进对生物量进行精确估算。用Chebyshev多项式系的组合构建了p维连续函数空间的一组乘积型基,进而建立了生物量估算统一模型,它具有如下特点:(1)可以克服常用生物量估算模型的经验性、不稳定性、不通用性及对生物量影响因素适应性差的特点,(2)它适合于影响生物量的任何因素,故适应范围非常广且很稳定,(3)可根据实际需要及估算精度确定影响生物量的因素及其阶数大小,(4)模型对生物量的估算相当于在区间[-1,1]上进行的数值插值,变量阶数越高,所插入的点就越多,估算结果越符合实际,整个估算的插值过程与树木的树干解析与树木生长原理是相一致的。对所建模型的参数辨识方法做了探讨,经典最小二乘算法是生物量估算的最常用参数辨识方法,由于它本身固有的一些缺陷使常用最小二乘的估算精度与使用范围受到很大的限制,现代多元统计分析的偏最小二乘算法可以克服常用最小二乘的缺陷,但在提取成分时仍具有不足,针对偏最小二乘的缺陷本文对它做了改进,改进算法即能克服偏最小二乘的不足还能使估算精度大大提高。用2个案例对3种生物量估算方法做了对比分析,结果表明生物量估算统一模型与偏最小二乘改进算法精度最高,其生物量估计误差在零附近排成一条直线。     

滴灌条件下温室番茄需水量估算模型

基于修正后的Pnman-Monteith方程,通过分析作物系数与积温的关系,构建了基于常规气象资料的滴灌条件下温室番茄需水量估算模型,并分别采用2009年5月2-13日(开花坐果期)和6月9-20日(成熟采摘期)2个时段内的实测蒸腾量和实测棵间土壤蒸发量对模型模拟结果进行验证.结果表明:修正后的Penman-Monteith方程适用于温室参考作物需水量(ET0)的计算;温室番茄作物系数与积温呈抛物线关系;所建需水量模型模拟值的平均相对误差小于10%,可用于估算滴灌条件下温室番茄需水量.     

毛竹林地上部分生物量遥感估算模型的可移植性

选择浙江省内临安、安吉、龙泉3个毛竹产区为研究区域,基于野外调查数据和Landsat 5 TM影像,分别建立3个区域的毛竹林生物量遥感估算模型,包括一元线性模型、一元非线性模型、逐步回归模型、多元线性模型和Erf-BP神经网络模型,并对3个区域的模型进行评价;最后,选择精度较好的模型进行移植并对其可移植性进行分析.结果表明:在3个区域,Eff-BP神经网络模型精度均最高,逐步回归模型和一元非线性模型次之.Erf-BP神经网络模型的可移植性最佳.模型类型和模型自变量对统计模型的可移植性有较大影响.     

桉树叶片光合色素含量高光谱估算模型

色素在植物的生理生态过程中非常重要,利用高光谱数据,揭示光谱反射率上特征波段与光合色素含量间的关系将有助于理解光合色素光谱反射特征的规律,同时为利用高光谱遥感技术快速无损监测植物叶片光合色素提供了技术支持.利用野外采集的桉树叶片样本,在实验室内测定了叶片的高光谱反射率及对应的叶绿素、类胡萝卜素含量.利用光谱分析技术和统计学方法对光谱数据进行处理分析,提取了光谱特征参量,并建立叶绿素、类胡萝卜素含量与光谱特征参量间的估算模型.通过精度检验,研究结果表明以(SDr-SDb)/(SDr+SDb)为变量建立的指数模型估算效果最佳.     

北半球中高纬度的森林碳库可能远小于目前的估算

森林植被是陆地生物圈的主体,约有８５％的陆地生物量集中在森林植被（ Ｃａｏ＆ Ｗｏｏｄｗａｒｄ,１９９８）。由于他的巨大碳库作用,森林在全球碳循环中起着举足轻重的作用。准确地推算森林生物量和他的分布是解释全球碳收支计算仍存在不平衡问题的一个关键因素（Ｓｃｈｉｍｅｌ ｅｔ ａｌ, １９９５）,也是满足京都协定制定的ＣＯ２排放目标的急迫需要（Ｂｒｏｗｎ＆Ｓｃｈｒｏｅｄｅｒ,１９９９）。然而,有理由相信,全球森林生物量的推算仍存在很大的不准确性,这种不确定性的减少在很大程度上依赖于估测方法的改进和使用数据…     

Relation of transition probabilities in the Leslie model to those from experimental cumulative distributions

We explore the relationship between transition probabilities in the Leslie model and those derived from experimental cumulative distributions. The nature of the two kinds of probabilities are discussed, and a formula derived for converting from one to the other. A numerical example is given to illustrate the differences.     

Temperature response of the cell cycle of Haplopappus gracilis in suspension culture and its significance to the G1 transition probability model

The effects of temperature on the cell cycle of Haplopappus gracilis suspension cultures were analysed by the fraction of labelled mitoses method. Sphase in these cultures shows a different temperature optimum as compared to optima derived for G₂ and mitosis. G₁ phase has a much lower Q₁₀ than the other cell cycle phases and shows no temperature optimum between 22 and 34° C. These results are discussed in relation to a transition probability model of the cell cycle proposed by Smith and Martin (Proc. Natl. Acad. Sci. USA 70, 1263–1267, 1973), in which each cell has a time independent probability of initiating the transition into another round of DNA replication and division. The implications of such a model for cell cycle analysis are discussed and a tentative model for a probabilistic transition trigger is advanced.Abbreviations FLM Fraction of labelled mitoses - T_B Total B-phase     

Intramolecular alpha-helix-beta-structure-random coil transition in polypeptides. II. Dynamic case

The conformational changes of polypeptides which are capable of forming the alpha-helix. beta-structure and random coil (or the unordered) conformations are discussed. The kinetics of this system are studied as the time evolution of the probabilities describing the conformational states of the system. The time behavior of the average numbers of the alpha-helix and the beta-structure reveals the existence of intermediate states which are not found and not stable at equilibrium. These intermediates make the kinetics of this system more complex. Such situations can occur in protein folding and unfolding processes in such a way that a conformation absent in the tertiary structure appears in the intermediate stages and disappears finally, and the time course of the reaction is described by the sum of two or more exponential terms, in other words, the protein folding and unfolding processes display multiphasic kinetics. These intermediates, which are formed by short-range interactions, may usually be destroyed but sometimes can be stabilized by medium- and long-range interactions and remain stable for a fairly long time in the process of renaturation in real proteins.     

The relationship between the transition matrix model and the diffusion model

The diffusion equation model and the Lefkovitch matrix model have been employed independently in plant population ecology in order to analyze the dynamics of growth and size structure. The two models describe the dynamics of size structure in biological populations, and thus there must be some relationship between them. In the present paper, we examine the theoretical relationship between these two models. We demonstrate, on a certain assumption, that the one-step Lefkovitch matrix model corresponds to a difference equation of the diffusion equation and that the two- and three-step Lefkovitch matrix model correspond to difference equations of the 4th- and 6th-order Kramers-Moyal expansions, respectively. It is also shown that 2n moments (the first to the 2n-th moments) of growth rate are necessary and sufficient to rewrite uniquely the n-step Lefkovitch matrix model in terms of the linear combination of the moments. We finally discuss the relationship between the species characteristics of census data and the appropriate types of the Lefkovitch matrix.     

非线性状态方程模拟异龄林径阶动态--以长白山阔叶红松林为例

以矩阵模型为基础,利用林分直径生长、进界生长和枯损的资料。用非线性动态模型模拟长白山阔叶红松林动态生长,并预测短期内在不同的采伐强度下林分的径阶变化,分析不同采伐强度对年生长量、年收获量和恢复年数的影响。结果表明,非线性动态模型在模拟林分生长上具有结构严谨和精度高的优点。将模型推广到采伐林分中,为科学地经营阔叶红松林,制定合理的采伐方案提供科学依据。     

The probability of fixation of a single mutant in an exchangeable selection model

The Cannings exchangeable model for a finite population in discrete time is extended to incorporate selection. The probability of fixation of a mutant type is studied under the assumption of weak selection. An exact formula for the derivative of this probability with respect to the intensity of selection is deduced, and developed in the case of a single mutant. This formula is expressed in terms of mean coalescence times under neutrality assuming that the coefficient of selection for the mutant type has a derivative with respect to the intensity of selection that takes a polynomial form with respect to the frequency of the mutant type. An approximation is obtained in the case where this derivative is a continuous function of the mutant frequency and the population size is large. This approximation is consistent with a diffusion approximation under moment conditions on the number of descendants of a single individual in one time step. Applications to evolutionary game theory in finite populations are presented.      

The survival probability of a mutant in a multidimensional population

We prove a general result about the asymptotic behaviour of the survival probability of a slightly supercritical multitype Bienaymé-Galton-Watson branching process. This is the complete analogue of a result which Ewens (1968) obtained for a Poisson branching process.Research supported by NSERC     

A phase transition for a random cluster model on phylogenetic trees

We investigate a simple model that generates random partitions of the leaf set of a tree. Of particular interest is the reconstruction question: what number k of independent samples (partitions) are required to correctly reconstruct the underlying tree (with high probability)? We demonstrate a phase transition for k as a function of the mutation rate, from logarithmic to polynomial dependence on the size of the tree. We also describe a simple polynomial-time tree reconstruction algorithm that applies in the logarithmic region. This model and the associated reconstruction questions are motivated by a Markov model for genomic evolution in molecular biology.