柳杉—杉木混交林种间竞争的研究

以混交树种在正常林分中的蓄积量为其环境容纳量,采用蓄积量百分数求混交林种间竞争系数,用Lotka-Volterra竞争方程探讨柳杉－杉木混交林种间竞争关系。结果表明,平衡时,柳杉、杉木相对蓄积量分别为76．21％和32．79％, 说明两树种能协调生长。     

沙地云杉种内、种间竞争的研究

根据调查资料,采用Ｈｅｇｙｉ提出的单木竞争指数模型ＣＩ＝∑Ｎｊ＝１（Ｄｊ／Ｄｉ）１Ｌｉｊ对内蒙古白音敖包自然保护区的沙地云杉种内、种间的竞争强度进行定量分析。结果表明：沙地云杉种内竞争强度随着林木径级的增大而逐渐减小;种内竞争和种间竞争的强度顺序为：山杨＞沙地云杉种内＞白桦＞家榆。竞争强度与对象木的胸高直径服从幂函数关系ＣＩ＝ＡＤ－Ｂ,当沙地云杉胸高直径达到４０ｃｍ以上时,竞争强度变化很小。利用模型预测了沙地云杉种内、种间的竞争强度。说明Ｈｅｇｙｉ的单木竞争模型可为种内、种间竞争指数的研究提供可适用的数量指标。     

水曲柳落叶松人工混交林中树木个体生长的竞争效应模型

本研究从水曲柳落叶松混交林中树木的种内种间竞争机制出发,对与距离有关的竞争模型和邻体干扰模型进行了改进,提出了以竞争指数分量和竞争效应系数来量化树木间的空间竞争。根据野外的实测数据,以年材积生长量为因变量各竞争指数分量为自变量,通过多元回归分析建立了树木个体生长的竞争效应模型,回归结果有很好的拟合优度。本研究为空间竞争模型的进一步改进和生态学研究植物竞争生长关系提供了新的思路。     

阔叶红松林树种间竞争关系及其营林意义

竞争是森林生态系统中的普遍现象 ,其结果是一个有机体阻碍另一个有机体的正常生长和发育[9] 。在生态学上 ,多年来对树种间竞争的研究一直局限于实验的方法 ,而在竞争强度上缺乏数量指标[2 ] 。 2 0世纪 60年代以来 ,很多学者为了更准确地预测林木生长 ,相继提出了许多描述林木间竞争强度的数量指标 ,即竞争指数系统 ,从而形成了用单木生长模型来预测林木生长的方法[2 ,3 ] 。特别是Ｈｅｇｙｉ提出的竞争指数模型对于定量描述树种间的竞争强度有着十分重要的意义。在长白山地区 ,从海拔 5 0 0～ 110 0ｍ分布有温带地区的地带性顶极植被阔叶…     

元宝山冷杉群落种内与种间竞争的数量关系

元宝山冷杉 (AbiesyuanbaoshanensisY .J .LuetL .K .Fu)特产广西 ,是种群数量极少的濒危物种。根据调查资料 ,采用Hegyi提出的单木竞争指数模型CI=∑Nj=1 (Dj/Di)·1Lij对元宝山冷杉群落的种间、种内竞争强度进行定量分析。结果表明 :元宝山冷杉种内竞争较之与其伴生树种间的竞争剧烈 ;竞争木对对象木的竞争强度与对象木的胸高直径服从幂函数关系CI=ADB,竞争强度随对象木个体的增大而减小。当元宝山冷杉胸高直径达到 35～ 40cm后 ,竞争强度变化不明显。利用模型预测了元宝山冷杉种内和种间的竞争强度     

子午岭天然油松林乔木层种内与种间竞争关系研究

采用改进的竞争指数模型研究了甘肃省子午岭天然油松林乔木层种内和种间竞争强度。结果发现:(1)随对象木胸径的增大,油松种群因自疏作用使植株距离增加,种内竞争强度降低。(2)油松群落内其它物种虽较多,但个体普遍较小,种间竞争相对较弱,种内与种间竞争关系顺序为:油松种内>辽东栎>漆树>春榆。(3)竞争强度与对象木胸径的关系服从幂函数关系,当油松胸径达25cm以上时,竞争强度变化不大,所得的预测模型能很好地预测油松种内和种间的竞争强度。(4)改进的竞争指数模型能很好地度量油松的种内和种间竞争强度。     

资源竞争理论及其研究进展

介绍了国外近20年来发展起来的一种新的竞争理论——资源竞争理论。该理论包含两个主要假说,即R^*-法则和资源比假说。资源竞争理论已在微生物、微藻、高等植物及浮游动物中得到广泛的实验验证。阐述了资源竞争理论形成的基础——Monod竞争模型和Droop竞争模型。对两种模型在稳态及非稳态条件下的预测性能作了比较：对于稳态下的竞争,两种模型皆能做出较好的预测,但使用Monod模型更为简便;对于非稳态下的竞争,使用Droop模型更为合理。对资源竞争理论的发展趋势作了展望。     

植物地上竞争与地下竞争研究进展

植物地上光竞争和地下水分与营养的竞争过程十分复杂,并且与竞争机制密切相关。从地上和地下竞争理论、两种竞争过程的相互作用机制以及分离地上和地下竞争的研究方法和表达指标等几个方面综述和分析目前的研究状况,以期为国内研究者在本领域进一步展开实验提供理论依据和实验设计参考。总结了与地上、地下相对竞争强度有关的优化分配理论,地上、地下竞争随生产力梯度的变化,资源异质性对地上、地下竞争机制的影响。介绍了地上竞争和地下竞争相互作用类型以及目前提出的两种作用机制。对常用的3种分离地上、地下竞争的方法:盆分隔、间植分隔和目标植分隔法以及表达竞争强度和竞争重要性的指标和公式进行了归纳。提出未来的研究内容,认为在开展此类研究时,应考虑到实验植物的生理学特性、发育状况、立地生产力跨度范围以及竞争持续时间等方面因素,并认为发展地下竞争研究、深入探讨根系间相互作用的影响因子和过程是当前的研究热点。     

天柱山黄山松种内与种间竞争的研究

采用改进的竞争指数模型研究安徽天柱山黄山松的种内和种间竞争强度。结果发现:(1)随对象木胸径的增大,黄山松种群因自然稀疏过程中密度调节作用,植株距离增加,种内竞争强度降低;(2)黄山松群落内其它物种虽然较多,但个体普遍较小,结果种间竞争相对较弱,种内与种间竞争关系顺序为:黄山松—黄山松>杉木—黄山松>枹栎—黄山松>其它树种—黄山松;(3)竞争强度和对象木胸径的关系服从幂函数关系(CI=AD-B),当黄山松胸径达到20cm以上时,竞争强度变化不大,所得的预测模型能很好地预测黄山松种内和种间的竞争强度;(4)改进的竞争指数模型能很好地度量黄山松的种内和种间竞争强度,改进的确定邻体范围的方法能有效地确定黄山松的竞争范围。     

基于引力模型的林木竞争分析

引力模型是否可以应用于森林群落林木竞争关系分析是值得研究的问题。基于引力模型建立林木相对活力圈能反映竞争木活力大小,基于竞争木的相对活力圈建立引力竞争指数能准确反映林木生长与林木竞争的关系。以浙江省天目山国家级自然保护区针阔混交林为研究对象,将V_Hegyi竞争指数、引力竞争指数分别与胸径进行相关分析,胸高断面积生长量分别与2种竞争指数进行相关分析,胸径生长率与2期引力竞争指数的比值(2021年与2006年的引力竞争指数之比)进行相关分析,此外,对相对活力圈直径与胸径进行相关分析,并比较分析了活立木与枯死木的竞争指数大小。结果表明: 2种竞争指数与胸径均呈显著负相关,且均服从幂函数关系。林木胸高断面积生长量与2种竞争指数均呈显著负相关,但引力竞争指数比V_Hegyi竞争指数更能反映林木生长与林木竞争的关系。相对于V_Hegyi竞争指数的比值,2期引力竞争指数的比值更能说明林木生长与林木竞争的关系。在针阔混交林中,阔叶树种的生长与竞争的相关性>针叶树种生长与竞争的相关性。林木枯损受竞争的显著影响。林木相对活力圈大小与林木胸径大小呈显著负相关。引力模型是反映空间相互作用的重要模型之一,可以应用于林木竞争关系的研究,且基于引力模型建立的引力竞争指数可以作为评价林木竞争和林木活力的一个空间结构指标,比V_Hegyi竞争指数更能反映林木生长与林木竞争的关系。     

Community diversity and total abundance: Quantitative predictions from competition niche theory

Lotka–Volterra niche competition theory (LVNCT) is based on Lotka–Volterra competition equations with competition coefficients between pairs of species determined by the intensity of their niche overlap though the MacArthur–Levins niche overlap formula. Here I study analytically and numerically the predictions of LVNCT concerning total abundance and biodiversity, measured by the Shannon equitability index. Firstly, a set of simplifying assumptions that render the LVNCT amenable of analytical treatment are considered. In particular I derive an approximated formula for the total abundance, as the inverse of the mean value of the interspecific competition coefficients, which works pretty well both for the transient and steady regime and for a wide range of the typical niche width σ. Secondly, I analyze, by means of simulations, the effect of relaxing the above simplifying assumptions when considering more realistic conditions. It turns out that the approximated formula for the total abundance is quite robust and its potential implications for management are discussed. I also analyze the predicted relationship between community productivity and diversity.     

Evolutionary disarmament in interspecific competition.

Competitive asymmetry, which is the advantage of having a larger body or stronger weaponry than a contestant, drives spectacular evolutionary arms races in intraspecific competition. Similar asymmetries are well documented in interspecific competition, yet they seldom lead to exaggerated traits. Here we demonstrate that two species with substantially different size may undergo parallel coevolution towards a smaller size under the same ecological conditions where a single species would exhibit an evolutionary arms race. We show that disarmament occurs for a wide range of parameters in an ecologically explicit model of competition for a single shared resource; disarmament also occurs in a simple Lotka-Volterra competition model. A key property of both models is the interplay between evolutionary dynamics and population density. The mechanism does not rely on very specific features of the model. Thus, evolutionary disarmament may be widespread and may help to explain the lack of interspecific arms races.     

An alternative to Lotka-Volterra competition in coarse-grained environments

Competition in a coarse-grained heterogeneous environment is considered. It is assumed that each individual adjust has position within the macrohabitat so as to try to maximize a utility whose value is a function of position within the habitat and of the population density at that position. Robust qualitative conclusions concerning the resulting population behavior relate niche breadth, niche shift, and resource partitioning to changes in population numbers. In particular populations avoid competition by reducing coarse-grained niche overlap so that overlap is a measure not of the degree of competition but of its absence. Specific models of exploitation or interference competition give specific quantitative results which are summarized. Competition equations are derived from underlying models which imply Lotka-Volterra equations in a fine-grained environment (MacArthur, R., and Levins, R. 1967. Amer. Natur.101, 377–385) but which are nonlinear in per capita growth in a coarse-grained one. The findings are relevant to theoretical studies of competition, limiting similarity, species packing, and the evolution of niche position as well as to practical problems of data analysis and resource management. The extension to predator-prey interactions is outlined.     

一类具分段常数变量的捕食-食饵系统的Neimark-Sacker分支

讨论了具时滞与分段常数变量的捕食-食饵生态模型的稳定性及Neimark-Sacker分支;通过计算得到连续模型对应的差分模型,基于特征值理论和Schur-Cohn判据得到正平衡态局部渐进稳定的充分条件;以食饵的内禀增长率为分支参数,运用分支理论和中心流形定理分析了Neimark-Sacker分支的存在性与稳定性条件;通过举例和数值模拟验证了理论的正确性。     

Competition among the pioneers in a seasonal soft-bottom benthic succession: field experiments and analysis of the Gilpin-Ayala competition model

Summary Controlled experiments, designed to assess the effects of pioneers on succession on an intertidal sandflat, provided evidence for interspecific competition between juvenile Hobsonia florida (Polychaeta, Ampharetidae) and oligochaetes. The field data were fitted to both the linear Volterra and non-linear Gilpin-Ayala competition equations. With its greater number of parameters, the Gilpin-Ayala model must provide a better fit to observed population abundances. The Gilpin-Ayala model is flawed as an explanation of the population trajectories of the H. florida and oligochaetes, because its non-linearity parameter affects only intraspecific competion. With either model our field data demonstrate a solution to Hutchinson's paradox. With competition coefficients near unity and similar carrying capacities, the predicted population trajectories are heavily dependent on initial conditions. The predicted times to competitive exclusion are long and can easily exceed the typical period of environmental constancy. Our study offers evidence for Neill's competitive bottleneck: competition acts primarily on the developmental stages of one of a pair of competing species. The permanent meiofauna may act as a competitive bottleneck for the population growth of benthic macrofauna. The mechanism of this competitive interaction probably involves exploitative interspecific competition for benthic diatoms.     

A competition model for a seasonally fluctuating nutrient

A model of two species consuming a single, limited, periodically added resource is discussed. The model is based on chemostat-type equations, which differ from the classical models of Lotka and Volterra. The model incorporates nonlinear functional response curves of the Holling or Michaelis-Menten type to describe the dependence of the resource-exploitation rate on the amount of resource. Coexistence of two species due to seasonal variation is indicated by numerical studies.     

Biodiversity,habitat area,resource growth rate and interference competition

For the majority of species, per capita growth rate correlates negatively with population density. Although the popular logistic equation for the growth of a single species incorporates this intraspecific competition, multi-trophic models often ignore self-limitation of the consumers. Instead, these models often assume that the predator-prey interactions are purely exploitative, employing simple Lotka-Volterra forms in which consumer species lack intraspecific competition terms. Here we show that intraspecific interference competition can account for the stable coexistence of many consumer species on a single resource in a homogeneous environment. In addition, our work suggests a potential mechanism for field observations demonstrating that habitat area and resource productivity strongly positively correlate to biodiversity. In the special case of a modified Lotka-Volterra model describing multiple predators competing for a single resource, we present an ordering procedure that determines the deterministic fate of each specific consumer. Moreover, we find that the growth rate of a resource species is proportional to the maximum number of consumer species that resource can support. In the limiting case, when the resource growth rate is infinite, a model with intraspecific interference reduces to the conventional Lotka-Volterra competition model where there can be an unlimited number of coexisting consumers. This highlights the crucial role that resource growth rates may play in promoting coexistence of consumer species.     

Multiple infection dynamics has pronounced effects on the fitness of RNA viruses

Several factors play a role during the replication and transmission of RNA viruses. First, as a consequence of their enormous mutation rate, complex mixtures of genomes are generated immediately after infection of a new host. Secondly, differences in growth and competition rates drive the selection of certain genetic variants within an infected host. Thirdly, but not less important, a random sampling occurs at the moment of viral infectious passage from an infected to a healthy host. In addition, the availability of hosts also influences the fate of a given viral genotype. When new hosts are scarce, different viral genotypes might infect the same host, adding an extra complexity to the competition among genetic variants. We have employed a two‐fold approach to analyse the role played by each of these factors in the evolution of RNA viruses. First, we have derived a model that takes into account all the preceding factors. This model employs the classic Lotka‐Volterra competition equations but it also incorporates the effect of mutation during RNA replication, the effect of the stochastic sampling at the moment of infectious passage among hosts and, the effect of the type of infection (single, coinfection or superinfection). Secondly, the predictions of the model have been tested in an in vitro evolution experiment. Both theoretical and experimental results show that in infection passages with coinfection viral fitness increased more than in single infections. In contrast, infection passages with superinfection did not differ from the single infection. The coinfection frequency also affected the outcome: the larger the proportion of viruses coinfecting a host, the larger increase in fitness observed.     

Does population ecology have general laws?

There is a widespread opinion among ecologists that ecology lacks general laws. In this paper I argue that this opinion is mistaken. Taking the case of population dynamics, I point out that there are several very general law-like propositions that provide the theoretical basis for most population dynamics models that were developed to address specific issues. Some of these foundational principles, like the law of exponential growth, are logically very similar to certain laws of physics (Newton's law of inertia, for example, is almost a direct analogue of exponential growth). I discuss two other principles (population self-limitation and resource-consumer oscillations), as well as the more elementary postulates that underlie them. None of the "laws" that I propose for population ecology are new. Collectively ecologists have been using these general principles in guiding development of their models and experiments since the days of Lotka, Volterra, and Gause.