斑苦竹无性系种群克隆繁殖的动态与调节研究

本文依据了ＪＬＨａｒｐｅｒ（１９７７）的构件生物（ｍａｄｕｌａｒｏｒｇａｎｉｓｍ）种群理论,将某一特定生境内的斑苦竹竹子的集合作为一个无性系种群,研究了它的克隆繁殖构件的数量动态,以及克隆繁殖与无性系基株年龄和分株密度的关系。结果表明：斑苦竹以Ⅲ龄级基株形成的克隆繁殖构件（笋芽）数量最多,以后,随龄级的增大而逐渐减少。发笋数、退笋数和成竹数均与无性系分株密度相关,它们的最适密度都为２５×１０４株／ｈａ。退笋率和成竹率与繁殖构件的出土时间呈直线相关关系。退笋率模型：Ｄ＝２７．２５３＋０．７０２ｔ（Ｒ２＝０．６３６）成竹率模型：Ｍ＝７２．６６２－０．７０１ｔ（Ｒ２＝０．６３４）     

斑苦竹(Pleioblastus maculata)无性系种群的数量和年龄结构动态

依据Ｈａｒｐｅｒ（１９７７）提出的构件生物种群理论,将源于同一地下根茎的每一竹子个构件。把斑苦竹竹子构件无性系种各的生活史小循环划分为８个阶段,用Ｌｅｓｌｉｅ矩阵表 预测了四川晋云山该种群的数量和年龄结构变化趋势。结果表明,用Ｌｅｓｌｉｅ矩阵来预测靠无性繁殖来扩大种群数量的竹类植物的年龄结构和数量动态,具有较高的可靠性。     

斑苦竹无性系生长与水分供应及其适应对策的研究

 根据对混生型斑苦竹(Pleioblastus maculata)移栽于不同土壤水分含量的微生境中的野外实验,分析了斑苦竹的无性系生长对水分资源供应的形态可塑性反应和能量投资对策。研究结果表明,水分资源供应水平越高,斑苦竹无性系的总生物量越大,同时,无性系分株的数目越少,而个体增大。在不同水分供应条件下,无性系的隔离者(地下根茎)长度和分株大小都具有显著的差异,而隔离者的节间长度则无明显差别。在低水分资源的生境中,斑苦竹无性系具有投资更多的能量于地下部分,尤其是根茎节间,从而伸长根茎,以获取资源的觅养生长对策;在高水分资源的生境中,其无性系的能量则主要投资于分株的生长。     

永瓣藤的地理分布及其种群空间格局

应用Ｇｒｅｉｇ－Ｓｍｉｔｈ邻接格子取样法,研究了我国珍稀植物永瓣藤（ＭｏｎｉｍｏｐｅｔａｌｕｎｃｈｉｎｅｎｓｅＲｅｈｄ）,的地理分布和种群空间格局及其形成机制,分析了其克隆生长格局和生态适应对策,研究结果表明,永瓣藤的分布区域狭窄,其种群空间格局为集群型,克隆生长格避为游击式稀疏形式样式,这与其生物学特性和种群生态适应的对策密切相关。     

敦煌阳关盐沼湿地芦苇种群小尺度空间分布格局

植物种群的空间分布格局是研究连接植物与外界环境关系的重要桥梁,是植物种群稳定性和生活史策略的表现形式。本研究以敦煌阳关盐沼湿地克隆植物芦苇(Phragmites australis)为对象,设置湿生区、轻度盐化区、重度盐化区和荒漠区采样梯度,应用Ripley K(d)函数分析法研究了芦苇种群的小尺度空间分布格局特征及生态适应对策。结果表明:(1)随着从湿生到荒漠区环境梯度的变化,芦苇种群的盖度、密度、高度、地上生物量及种群领地面积都呈现出显著下降的趋势,空斑面积呈现出显著增加的趋势,而种群领地密度则呈现出先增加后下降的趋势;(2)从湿生到荒漠生境,芦苇种群的小尺度空间拓展策略主要表现为由聚集分布为主、非聚集分布(随机分布或均匀分布)为辅,转变为随机分布为主、非随机分布(聚集分布或均匀分布)为辅的特征。研究结果明晰了干旱区内陆河湿地中芦苇种群的空间分布格局特点及其影响因素,为进一步理解克隆植物的生态适应机制提供了案例研究,为科学保护和管理干旱区内陆河湿地生态系统提供了理论依据。     

竹类植物种群生态学研究进展与展望

综述了竹类种群生理生态学、种群动态、繁殖特性、无性系种群特征等几个方面的研究进展,概括了群落水平上竹类种群对森林更新的影响。并从竹类种群克隆多样性与微进化、生长适应机理、开花机制,以及竹类种群与林窗更新等四个方面展望未来竹类种群生态学研究的重点和主要趋势。     

羊草无性系植物种群觅养生长格局与资源分配的研究

 本文按照理论种群生态学的研究方法,从生长参数的形态功能变化和发育参数的时间变化入手,系统地研究了羊草无性系植物种群觅养生长格局与资源分配的基本规律。研究结果表明,羊草无性系种群适合于用ψ＝0.5、μ=1.0、Tr=7和Ts＝2的分配函数模型描述其觅养生长格局与资源分配。文中建立了大小—制约分配模型,并用此模型预测了与觅养生长格局有关的资源分配。这一研究深刻地揭示了较为动物种群搜索途径复杂得多的无性系植物种群的觅养行为。     

羊草种群无性系生长格局的研究

 本文根据野外实测数据和采用数学分析方法,在研究羊草种群无性系营养扩散和生长过程的基础上,建立了符合描述羊草种群无性系生长格局的相关随机走动模型和简单扩散模型。对模型进行检验,结果表明,所建模型可以定量地描述羊草种群无性系的生长格局。     

外部干扰对根茎型克隆植物甘草自然种群植株生长及主要药用成分含量的影响

克隆植物, 特别是游击型克隆植物, 其分株在一定时间段往往通过连接结构(即间隔子)连接在一起形成克隆网络, 基于克隆网络的克隆植物特性显著提高了克隆植物应对外部干扰的能力。长期封育禁牧使得甘草(Glycyrrhiza uralensis)自然种群免受外部干扰, 却并没有促使受破坏的甘草自然种群快速恢复。因为克隆整合、克隆储存及克隆分株的选择性放置等克隆植物特性的存在, 适度的外部干扰有利于根茎型克隆植物甘草的生长与繁衍。但外部干扰与克隆植物特性在甘草种群恢复中的作用及其机理目前并不清楚。该研究以甘草自然种群为研究对象, 通过野外控制实验进行模拟动物采食和人工采挖干扰, 探讨不同程度干扰对甘草自然种群生长和主要药用成分含量的影响。结果表明在中度放牧采食干扰或者人工采挖干扰下, 甘草自然种群的分株密度、高度和地上生物量与对照相比均没有显著差异, 甘草表现出等补偿生长; 而在不同类型的重度干扰下, 甘草产生的响应不一致。重度放牧采食干扰下甘草表现出欠补偿生长, 而重度人工采挖干扰下甘草表现出超补偿生长。克隆植物特性在甘草应对外部干扰过程中发挥着重要作用。外部干扰一定程度上提高了甘草中甘草苷和甘草酸的含量, 从而提升了药材的品质。进一步的研究应该关注于甘草自然种群与环境因子之间的关系, 解析甘草自然种群退化的原因, 提出相应的复壮技术, 探讨可持续利用的管理模式。     

广东鹅凰嶂自然保护区杜鹃红山茶种群结构与空间分布格局

研究了广东鹅凰嶂省级自然保护区杜鹃红山茶天然种群的基径、高度和冠幅结构,应用扩散系数、负二次指数、Cassie指数、丛生指数、平均拥挤度、聚块性指数和格林指数等聚集度指标测定了种群空间分布格局及其动态.结果表明:在天然分布区内,杜鹃红山茶种群以成年树为主体,幼苗严重缺乏,表现为衰退趋势,但不同地段中种群的径级、高度和冠幅结构不完全相同.不同地段中杜鹃红山茶种群空间分布格局表现为聚集分布或随机分布;在种群生长过程中,分布格局从聚集型向随机型转变.     

Growth and competition in clonal plants-persistence of shoot populations and species diversity

This paper reviews studies on growth and size-structure dynamics of shoots and clones in clonal plants in comparison with those in non-clonal plants, and discusses the characteristics of clonal plants. The mode of competition between individuals (symmetric versus asymmetric, degree of competitive asymmetry), growth dynamics of individuals, allocation pattern between organs and spatial pattern of individuals are closely correlated with each other in non-clonal plant populations. Theoretical and field studies based on the diffusion model revealed that plants of “height-growth” type (mostly early-successional tree species) and plants of “diameter-growth” type (mostly late-successional tree species) tend to exhibit asymmetric competition and symmetric competition respectively. Moreover, asymmetrically competing plants show smaller effects of variation in individual growth rate and spatial pattern on the size-structure dynamics of the population than symmetrically competing plants. Thefefore, the spatial pattern of inviduals should be considered especially for plants undergoing symmetric competition. These results for non-clonal plants should have a significant implication also for the growth dynamics and competition in clonal plants. The mean growth rate of shoots [G(t,x) function] and hence the mode of competition between shoots differs among clonal plant species as in non-clonal plants. However, a large magnitude and size-independence (or slightly negative size-dependence) of the variation in growth rate of shoots [D(t,x) function], especially at the early stage in a growing season is a common characteristic of many clonal plant species, in contrast to the positively size-dependent variation in individual growth rate in non-clonal plants. This type of variation in shoot growth rate leads to the persistence of stable shoot populations even when the mean growth rate function is changed, and also in cases where the shoot population structure would be unstable in the absence of variation in growth rate. It is suggested that competition between clones is symmetric in most clonal plant species, which brings about small-scale spatio-temporal changes in species abundance and hence species diversity.     

Demography and modelling of clonal fragments in the pseudoannual plant shape Trientalis europaea L.

The clonal growth pattern and demography of clonal fragments (aggregation of ramets derived from a common parent ramet) in the pseudoannual plant Trientalis europaea were studied in field conditions from 1991 to 1993. During this period the population of clonal fragments declined, with a half-life of 7.4 years. Number and size of the clonal progeny and stolon length were positively related to the size of the mother ramet. Survival rates of ramets and tubers increased with size. The rate of clonal growth was low: after three years, about 70% of the clonal fragments had only one ramet. This suggests that the pseudoannual growth habit in T. europaea is more important as mechanism of perennation than of ramet multiplication.Field data were used in a simulation model of architecture and population dynamics of clonal fragments. About 10% of the clonal fragments survived to the end of the simulation (15 years) and the mean survival was 4.7 years. The model predicted a positive correlation between persistence of the clonal fragment and number of ramets produced. Sensitivity analysis showed that the production of a daughter ramet of at least the same size as the parent ramet was the most important pathway for the survival and the number of ramets of the clonal fragment, whereas the production of secondary ramets had a very small effect. This confirms the interpretation of the pseudoannual life-cycle as a mechanism of ramet replacement in this species. Sensitivity analysis also revealed that changes in survival probabilities of the smallest ramets had the largest impact on clonal fragment dynamics. This reflects the important role of the smallest size class of ramets as a source of new vegetative propagules, maintaining a hierarchy in the size structure of the population.     

The relative importance of sexual and clonal reproduction for population growth in the perennial herb Fragaria vesca

The relative importance of sexual and clonal reproduction for population growth in clonal plants is highly variable. Clonal reproduction is often more important than sexual reproduction but there is considerable interspecific variation and the importance of the two reproductive modes can change with environmental conditions. We carried out a demographic study on the woodland strawberry (Fragaria vesca), a widespread clonal herb, at 12 sites in Switzerland during 2 years. Study sites were selected in two different habitats, i.e., forest and forest edge. We used periodic matrix models to estimate annual population growth rates and carried out prospective analyses to identify life cycle components that influence population growth rates most. Retrospective analyses were applied to study how the two different habitats affected population dynamics. Furthermore, we tested whether trade-offs between sexual and clonal reproduction occurred. There were large differences in annual population growth rates between sites and large within-site differences between years. Results of the prospective analyses clearly indicate that clonal reproduction is the dominant reproductive pathway whereas sexual reproduction is rather insignificant for population growth. Compared to forest habitats, forest edge habitats had higher population growth rates in the first year but smaller growth rates in the second year. We attribute these differing habitat effects to different water availabilities during consecutive years. No trade-offs between sexual and clonal reproduction were found. In conclusion, population growth of F. vesca relies heavily on clonal reproduction. Furthermore, reproduction and survival rates of F. vesca depend highly on spatio-temporal variation of environmental conditions.     

Longevity of clonal plants: why it matters and how to measure it

Background

Species'' life-history and population dynamics are strongly shaped by the longevity of individuals, but life span is one of the least accessible demographic traits, particularly in clonal plants. Continuous vegetative reproduction of genets enables persistence despite low or no sexual reproduction, affecting genet turnover rates and population stability. Therefore, the longevity of clonal plants is of considerable biological interest, but remains relatively poorly known.

Scope

Here, we critically review the present knowledge on the longevity of clonal plants and discuss its importance for population persistence. Direct life-span measurements such as growth-ring analysis in woody plants are relatively easy to take, although, for many clonal plants, these methods are not adequate due to the variable growth pattern of ramets and difficult genet identification. Recently, indirect methods have been introduced in which genet size and annual shoot increments are used to estimate genet age. These methods, often based on molecular techniques, allow the investigation of genet size and age structure of whole populations, a crucial issue for understanding their viability and persistence. However, indirect estimates of clonal longevity are impeded because the process of ageing in clonal plants is still poorly understood and because their size and age are not always well correlated. Alternative estimators for genet life span such as somatic mutations have recently been suggested.

Conclusions

Empirical knowledge on the longevity of clonal species has increased considerably in the last few years. Maximum age estimates are an indicator of population persistence, but are not sufficient to evaluate turnover rates and the ability of long-lived clonal plants to enhance community stability and ecosystem resilience. In order to understand the dynamics of populations it will be necessary to measure genet size and age structure, not only life spans of single individuals, and to use such data for modelling of genet dynamics.     

慈竹克隆种群能量动态研究

本文引用Ｈａｒｐｅｒ的构件结构理论,从克隆构件,克隆分株和克隆种群３个层次,系统探索我国特有种慈竹克隆种群能量动态,研究结果表明：慈竹克隆种群单位量能值变化随其生长季节,生长发育阶段和年龄不同而异,冬季单位能值升高,换叶期单位能值聚然下降;生殖阶段单位能值降低,但龄级间差异较大,慈竹克隆种群具整合作用。影响慈竹克隆种群能量变动的因素主要是大气温度,湿度和种群生殖与换叶等。     

The influence of host dynamics on the clonal composition of Escherichia coli populations

Species, be they plant or animal, vary in their capacity for population growth or decline. Populations of the same species may also differ in their capacity for population change. A series of mathematical models were developed with the aim of determining if host population dynamics could influence the clonal composition of the Escherichia coli community in that host population. The biological assumptions underlying the models are described in some detail. Analytical and numerical approaches were used to investigate the behaviour of these models. The results demonstrate that host dynamics can have a profound influence on the E. coli clonal composition of the host population. This outcome is largely independent of the nature of the assumptions underlying the models. The ways in which the predictions of these models may be tested empirically are discussed, as are the implications of these models for understanding the nature of host-bacterial pathogen dynamics.     

THE DEVELOPMENT OF SPATIAL PATTERN IN CLONES OF AN AQUATIC PLANT,EICHHORNIA CRASSIPES SOLMS

The spatial geometry of clonal growth of Eichhornia crassipes, a plant which increases in number by the vegetative production of stolon offshoots (or ramets), was assessed by the use of a vector analysis. Growth of water hyacinth clones was found to be asymmetric, asymmetry increasing with time. The direction of asymmetry was independent of either population density or the position of nearest neighbors. The analysis revealed the importance of geometric relationships within the parental growth axis for determining patterns of clonal spread. Meristem growth and differentiation appear to be controlled so as to maximize clonal growth rate. This contrasts with the patterns observed in rhizomatous terrestrial species in which the control of meristem growth and differentiation appears to result in efficient use of space at the expense of greater increase in clonal size.     

Population structure and dynamics of the clonal dwarf-shrub Linnaea borealis

Abstract. The demography of the long-lived clonal dwarf-shrub Linnaea borealis was studied during four years in a coniferous forest in central Sweden. The main object was to infer patterns of temporal variation in population dynamics of this species. The shoot population is organized in fragments, i.e. physically connected systems of shoots partly covered by the moss carpet. The age and size structure of the fragment population is described, but shoots are more convenient units for a study of population dynamics. A stochastic model of shoot population dynamics was constructed, and simulations indicated a considerable temporal variation in population size and flowering. Hence, variability as such is an essential aspect of the dynamics of established populations of Linnaea. Simulations of extinction risks revealed that small-sized shoot populations (ca. 250 shoots) are likely to be long-lived when experiencing environmentally induced demographic variation of the range observed. Mortality agents for established genets, such as large-scale disturbances, were not incorporated in the models. Some implications of variable population growth rates in clonal plants in woodlands are discussed.     

Demographic vulnerability of the clonal and endangered meadow thistle

For effective management of endangered species it is pivotal to understand why a species is endangered and which key life cycle components are involved in its response to environmental changes. Our objective was to investigate the response of rosettes of the redlisted clonal herb Cirsium dissectum to anthropogenic nutrient enrichment, which threatens its populations, and the consequences of these responses for its population dynamics. We constructed matrix population models with demographic data from three populations and four annual transitions and we decomposed the spatiotemporal variation in projected population growth rates into contributions from life cycle components. These patterns were compared with below-ground rosette dynamics in different fields, and with the below- and above-ground rosette dynamics in a garden experiment with nutrient enrichment and competing grasses. The decomposition analysis revealed that increased clonal rosette formation and decreased rosette survival were driving the spatial variation in the population growth rate. Excavating the below-ground rhizome network revealed a higher rosette turn-over in experimentally fertilized garden plots, which not only resulted in increased plot-level extinction, but also in increased spread of the clonal offspring. This supported the observed trend among field populations: rosette formation trades off with rosette survival. Surviving seedlings were only found in areas where the topsoil had been removed. The endangered C. dissectum is vulnerable when its habitat becomes more productive, because this species does not have the necessary capability to build up biomass. Small-scale disturbances such as created by sod-cutting or trampling cattle are essential for seedling establishment and necessary to render the explorative strategy of rhizomatous clonal spread successful.