基于增强型BN的CTCS-1级ATP可靠性研究

结合CTCS-2级与CTCS-3级列控系统设计和运用经验,铁路总公司提出了CTCS-1级列控系统的研制需求,该系统车载ATP设备将取代LKJ与机车信号对既有线列车的控制.本文以CTCS-1级ATP为主要研究对象,对比分析模块级冗余与系统级冗余方案下CTCS-1级ATP系统可靠性.根据CTCS-1级列控系统总体技术方案,构建模块级冗余与系统级冗余ATP可靠性框图,建立对应增强型贝叶斯网络(BN)模型.借助增强型BN正向推理,求解两种设计方案下ATP可靠性定量指标,评估两种设计方案的优劣.利用增强型BN模型逆向推理,求解列车超速防护(ATP)设备故障下基本单元条件失效概率,查找两种冗余设计方案的潜在薄弱环节.评估结果表明:两种方案下CTCS-1级ATP RAM指标均满足需求规范要求,但采用模块级冗余设计的CTCS-1级ATP RAM指标更优;外围冷备模块条件失效率明显高于其他模块,为CTCS-1级ATP的薄弱环节.     

亚高寒草甸实验群落物种丰富度与生物量稳定性关系研究

为揭示植物群落中物种丰富度与生物量稳定性之间的关系及机制,采用盆栽方法探究了物种丰富度、物种组成及施肥对群落生物量稳定性的效应.结果表明:施肥对群落生物量稳定性有显著影响,而物种丰富度、物种组成仅在施肥情况下对群落生物量稳定性有显著影响.群落生物量稳定性主要由物种的异步性决定.施肥通过提高特定物种组成群落中物种的异步性影响了物种组成对群落生物量稳定性的效应.物种组成部分嵌套于物种丰富度中,物种组成对群落生物量稳定性的作用高于物种丰富度.推测物种丰富度对群落生物量稳定性的效应由施肥影响特定物种组成群落中的物种异步性决定.     

食物网与物种多样性和系统稳定性研究

围绕生物多样性主要问题--物种多样性和系统稳定性之间的关系从食物网的角度究,(1)生物多样性与系统稳定性之间的关系本世纪70年代以前,生态学家普遍认为,生态系统的稳定性随生物多样性的增加而提高;自70年代后期一些理论学家普遍向这一看法提出挑战以来,在这一问题上出现了两大阵营;(2)生物多样性--稳定性和食物网的关系从食物网的角度综述了近半个世纪来生物多样性对系统稳定性的影响的研究结果,随着两大阵营的出现,食物网理论也从当初的营养级越多系统越稳定的观点转变为食物网随着食物链复杂性的增加而降低,但仍有许多科学家坚持以往的观点;(3)生物多样性--稳定性关系和物种作用强度的关系把食物网量化后提出了物种间的相互作用强度的概念,研究发现一个生态系统是由这些强相互作用决定的,而大部分的弱相互作用对一个生态系统的稳定起影响作用;弱相互作用对系统的影响程度具有时空特异性.     

冗余理论及其在生态学上的应用

文章简要叙述了冗余理论的来源和基本内容,冗余产生的条件和相对性,冗余在生态系统不同层次上的表现形式,冗余理论在生态学上的应用,指出冗余理论与多样性理论相比能更好地解释生态系统的稳定性问题.     

破碎化生境对食物网中疾病传播动态的影响

生境破碎化已被证实是影响种群动态和食物网中物种共存的重要因素之一,同时疾病的传播对于种群动态的调节也具有非常重要的作用。文章基于集合种群模型,针对3种不同的资源-宿主/食饵-寄生-捕食者食物网结构,探讨了破碎化生境下物种共存模式与种群动态。模拟结果显示,不同营养级物种对生境破坏有不同程度的响应,营养级越高的物种对生境破碎化越敏感。此外,物种的扩散范围以及捕食者种群对食饵的偏好都会影响物种的续存。该结果在一定程度上丰富了宿主-寄生理论,对疾病的控制和物种保护提供了生态学理论依据。     

对生态系统及生物多样性等理论问题的探讨

在简述生态系统基本特征的基础上，对生态系统是非平衡系统，是典型的耗散自组织系统进行论述；并对系统有序、无序、混沌状态的概念和相关关系及渐变、突变、分岔的区别作解释。阐述生命自组织的基本特性及新种的形成过程，同时用熵值作为生物多样性评价指标，证明了一个系统的熵值增加，物种多样性就丰富，熵值减少，物种多样性就较差。笔还就生物多样性与生态系统的稳定性问题进行了讨论，认为生物多样性与生态系统的稳定性没有必然的联系。     

食物网与物种多样性和系统稳定性研究

围绕生物多样性主要问题——物种多样性和系统稳定性之间的关系从食物网的角度究,(1)生物多样性与系统稳定性之间的关系:本世纪70年代以前,生态学家普遍认为,生态系统的稳定性随生物多样性的增加而提高;自70年代后期一些理论学家普遍向这一看法提出挑战以来,在这一问题上出现了两大阵营;(2)生物多样性——稳定性和食物网的关系:从食物网的角度综述了近半个世纪来生物多样性对系统稳定性的影响的研究结果,随着两大阵营的出现,食物网理论也从当初的营养级越多系统越稳定的观点转变为食物网随着食物链复杂性的增加而降低,但仍有许多科学家坚持以往的观点;(3)生物多样性——稳定性关系和物种作用强度的关系:把食物网量化后提出了物种间的相互作用强度的概念,研究发现一个生态系统是由这些强相互作用决定的,而大部分的弱相互作用对一个生态系统的稳定起影响作用;弱相互作用对系统的影响程度具有时空特异性。     

面向用户的Web服务可靠性计算模型

基于SOA,从用户的角度分析并计算Web服务及其应用的可靠性.首先采用一种扩展的UDDI模型收集可靠性相关数据,计算基本服务的可靠性、转移失效率和转移概率.然后基于BPEL文档构造组合服务的结构图,定义其结构属性,将转移失效率作为基本服务可靠性的加权系数,给出各种结构的组合服务的可靠性计算公式.最后在此基础上设计可靠性预测的递归算法用于计算Web应用的可靠性.实验结果表明:基于结构图的方法具有简便性和易处理性.     

食物网与物种多样性和系统稳定性研究

围绕生物多样性主要问题——物种多样性和系统稳定性之间的关系从食物网的角度究，（1）生物多样性与系统稳定性之间的关系：本世纪70年代以前，生态学家普遍认为，生态系统的稳定性随生物多样性的增加而提高；自70年代后期一些理论学家普遍向这一看法提出挑战以来，在这一问题上出现了两大阵营；（2）生物多样性——稳定性和食物网的关系：从食物网的角度综述了近半个世纪来生物多样性对系统稳定性的影响的研究结果，随着两大阵营的出现，食物网理论也从当初的营养级越多系统越稳定的观点转变为食物网随着食物链复杂性的增加而降低，但仍有许多科学家坚持以往的观点；（3）生物多样性——稳定性关系和物种作用强度的关系：把食物网量化后提出了物种阃的相互作用强度的概念，研究发现一个生态系统是由这些强相互作用决定的，而大部分的弱相互作用对一个生态系统的稳定起影响作用；弱相互作用对系统的影响程度具有时空特异性。     

黄河三角洲植物多样性与生态系统多功能性间的关系

以生境多变的黄河三角洲自然保护区为研究地,对黄河三角洲植物群落进行野外调查,探究自然生态系统中植物多样性与生态系统多功能性之间的关系。研究发现,植物物种丰富度、植物多样性Shannon指数和Simpson指数都与生态系统多功能性呈显著的正相关关系,而植物物种丰富度对生态系统多功能性变化的解释量最大,表明生态系统同时维持和提供多种服务功能需要更多的植物物种数量来支撑。土壤盐分是影响黄河三角洲植物多样性和生态系统多功能性的主要环境因素,土壤盐分的升高直接引起植物多样性的降低,从而间接导致生态系统多功能性下降。     

Functional diversity governs ecosystem response to nutrient enrichment

The relationship between species diversity and ecosystem functioning is a central topic in ecology today. Classical approaches to studying ecosystem responses to nutrient enrichment have considered linear food chains. To what extent ecosystem structure, that is, the network of species interactions, affects such responses is currently unknown. This severely limits our ability to predict which species or functional groups will benefit or suffer from nutrient enrichment and to understand the underlying mechanisms. Here our approach takes ecosystem complexity into account by considering functional diversity at each trophic level. We conducted a mesocosm experiment to test the effects of nutrient enrichment in a lake ecosystem. We developed a model of intermediate complexity, which separates trophic levels into functional groups according to size and diet. This model successfully predicted the experimental results, whereas linear food-chain models did not. Our model shows the importance of functional diversity and indirect interactions in the response of ecosystems to perturbations, and indicates that new approaches are needed for the management of freshwater ecosystems subject to eutrophication.     

Ecosystem consequences of species richness and composition in pond food webs

Resolving current concerns about the role of biodiversity on ecosystems calls for understanding the separate roles of changes in species numbers and of composition. Recent work shows that primary productivity often, but not always, saturates with species richness within single trophic levels. However, any interpretation of such patterns must consider that variation in biodiversity is necessarily associated with changes in species composition (identity), and that changes in biodiversity often occur across multiple trophic levels. Here we present results from a mesocosm experiment in which we independently manipulated species richness and species composition across multiple trophic levels in pond food webs. In contrast to previous studies that focused on single trophic levels, we found that productivity is either idiosyncratic or increases with respect to species richness, and that richness influences trophic structure. However, the composition of species within richness levels can have equally or more marked effects on ecosystems than average effects of richness per se. Indirect evidence suggests that richness and associated changes in species composition affect ecosystem attributes through indirect effects and trophic interactions among species, features that are highly characteristic of natural, complex ecosystems.     

Bottom-up effects of plant diversity on multitrophic interactions in a biodiversity experiment

Biodiversity is rapidly declining, and this may negatively affect ecosystem processes, including economically important ecosystem services. Previous studies have shown that biodiversity has positive effects on organisms and processes across trophic levels. However, only a few studies have so far incorporated an explicit food-web perspective. In an eight-year biodiversity experiment, we studied an unprecedented range of above- and below-ground organisms and multitrophic interactions. A multitrophic data set originating from a single long-term experiment allows mechanistic insights that would not be gained from meta-analysis of different experiments. Here we show that plant diversity effects dampen with increasing trophic level and degree of omnivory. This was true both for abundance and species richness of organisms. Furthermore, we present comprehensive above-ground/below-ground biodiversity food webs. Both above ground and below ground, herbivores responded more strongly to changes in plant diversity than did carnivores or omnivores. Density and richness of carnivorous taxa was independent of vegetation structure. Below-ground responses to plant diversity were consistently weaker than above-ground responses. Responses to increasing plant diversity were generally positive, but were negative for biological invasion, pathogen infestation and hyperparasitism. Our results suggest that plant diversity has strong bottom-up effects on multitrophic interaction networks, with particularly strong effects on lower trophic levels. Effects on higher trophic levels are indirectly mediated through bottom-up trophic cascades.     

南海北部大陆架海洋生态系统Ecopath模型的应用与分析

过度捕捞和环境恶化导致渔业资源和海洋生态系统逆向发展。采用EwE5.1软件,对南海北部大陆架建立Ecopath(生态通道模型)模型。通过各级流量、生物量、生产量、捕捞量、系统总流量以及生态位和混和营养效应等方面的分析,得出营养流通主要有2种途径,肉食鱼类间饵料竞争非常激烈,低值鱼类间具相似的捕食压力,顶级捕食者对大部分鱼类负效应不明显。系统受过度捕捞渔业影响很大,并存在营养级I利用效率低和渔业资源小型化、低值化等不稳定的幼态特征。     

Biodiversity and ecosystem multifunctionality

Biodiversity loss can affect ecosystem functions and services. Individual ecosystem functions generally show a positive asymptotic relationship with increasing biodiversity, suggesting that some species are redundant. However, ecosystems are managed and conserved for multiple functions, which may require greater biodiversity. Here we present an analysis of published data from grassland biodiversity experiments, and show that ecosystem multifunctionality does require greater numbers of species. We analysed each ecosystem function alone to identify species with desirable effects. We then calculated the number of species with positive effects for all possible combinations of functions. Our results show appreciable differences in the sets of species influencing different ecosystem functions, with average proportional overlap of about 0.2 to 0.5. Consequently, as more ecosystem processes were included in our analysis, more species were found to affect overall functioning. Specifically, for all of the analysed experiments, there was a positive saturating relationship between the number of ecosystem processes considered and the number of species influencing overall functioning. We conclude that because different species often influence different functions, studies focusing on individual processes in isolation will underestimate levels of biodiversity required to maintain multifunctional ecosystems.     

Diversity-dependent production can decrease the stability of ecosystem functioning

There is concern that species loss may adversely affect ecosystem functioning and stability. But although there is evidence that biodiversity loss can lead to reductions in biomass production, there is no direct evidence that biodiversity loss affects ecosystem resistance (ability to withstand perturbation) or resilience (recovery from perturbation). Yet theory, laboratory experiments and indirect experimental evidence strongly suggest that diversity and stability are related. Here we report results from a field experiment with factorially crossed perturbation and diversity manipulations. We simulated drought perturbation on constructed grassland ecosystems containing 1, 2, 4, 8 or 32 plant species. Under unperturbed conditions, the species-poor systems achieved lower biomass production than the species-rich systems. However, the species-poor systems were more resistant to perturbation than the species-rich systems. The species-poor systems also showed a larger initial resilience following perturbation, although the original relationship between diversity and productivity was fully restored after 1year. Our results confirm that biodiversity increases biomass production, but they also point to the fact that such diversity--production associations may lead to an inverse relationship between biodiversity and the stability of ecosystem functioning.     

Ecosystem stability and compensatory effects in the Inner Mongolia grassland

Numerous studies have suggested that biodiversity reduces variability in ecosystem productivity through compensatory effects; that is, a species increases in its abundance in response to the reduction of another in a fluctuating environment. But this view has been challenged on several grounds. Because most studies have been based on artificially constructed grasslands with short duration, long-term studies of natural ecosystems are needed. On the basis of a 24-year study of the Inner Mongolia grassland, here we present three key findings. First, that January-July precipitation is the primary climatic factor causing fluctuations in community biomass production; second, that ecosystem stability (conversely related to variability in community biomass production) increases progressively along the hierarchy of organizational levels (that is, from species to functional group to whole community); and finally, that the community-level stability seems to arise from compensatory interactions among major components at both species and functional group levels. From a hierarchical perspective, our results corroborate some previous findings of compensatory effects. Undisturbed mature steppe ecosystems seem to culminate with high biodiversity, productivity and ecosystem stability concurrently. Because these relationships are correlational, further studies are necessary to verify the causation among these factors. Our study provides new insights for better management and restoration of the rapidly degrading Inner Mongolia grassland.     

Transient dynamics of an altered large marine ecosystem

Overfishing of large-bodied benthic fishes and their subsequent population collapses on the Scotian Shelf of Canada's east coast and elsewhere resulted in restructuring of entire food webs now dominated by planktivorous, forage fish species and macroinvertebrates. Despite the imposition of strict management measures in force since the early 1990s, the Scotian Shelf ecosystem has not reverted back to its former structure. Here we provide evidence of the transient nature of this ecosystem and its current return path towards benthic fish species domination. The prolonged duration of the altered food web, and its current recovery, was and is being governed by the oscillatory, runaway consumption dynamics of the forage fish complex. These erupting forage species, which reached biomass levels 900% greater than those prevalent during the pre-collapse years of large benthic predators, are now in decline, having outstripped their zooplankton food supply. This dampening, and the associated reduction in the intensity of predation, was accompanied by lagged increases in species abundances at both lower and higher trophic levels, first witnessed in zooplankton and then in large-bodied predators, all consistent with a return towards the earlier ecosystem structure. We conclude that the reversibility of perturbed ecosystems can occur and that this bodes well for other collapsed fisheries.     

Trophic cascades across ecosystems

Predation can be intense, creating strong direct and indirect effects throughout food webs. In addition, ecologists increasingly recognize that fluxes of organisms across ecosystem boundaries can have major consequences for community dynamics. Species with complex life histories often shift habitats during their life cycles and provide potent conduits coupling ecosystems. Thus, local interactions that affect predator abundance in one ecosystem (for example a larval habitat) may have reverberating effects in another (for example an adult habitat). Here we show that fish indirectly facilitate terrestrial plant reproduction through cascading trophic interactions across ecosystem boundaries. Fish reduce larval dragonfly abundances in ponds, leading to fewer adult dragonflies nearby. Adult dragonflies consume insect pollinators and alter their foraging behaviour. As a result, plants near ponds with fish receive more pollinator visits and are less pollen limited than plants near fish-free ponds. Our results confirm that strong species interactions can reverberate across ecosystems, and emphasize the importance of landscape-level processes in driving local species interactions.     

Effects of biodiversity on the functioning of trophic groups and ecosystems

Over the past decade, accelerating rates of species extinction have prompted an increasing number of studies to reduce species diversity experimentally and examine how this alters the efficiency by which communities capture resources and convert those into biomass. So far, the generality of patterns and processes observed in individual studies have been the subjects of considerable debate. Here we present a formal meta-analysis of studies that have experimentally manipulated species diversity to examine how it affects the functioning of numerous trophic groups in multiple types of ecosystem. We show that the average effect of decreasing species richness is to decrease the abundance or biomass of the focal trophic group, leading to less complete depletion of resources used by that group. At the same time, analyses reveal that the standing stock of, and resource depletion by, the most species-rich polyculture tends to be no different from that of the single most productive species used in an experiment. Of the known mechanisms that might explain these trends, results are most consistent with what is called the 'sampling effect', which occurs when diverse communities are more likely to contain and become dominated by the most productive species. Whether this mechanism is widespread in natural communities is currently controversial. Patterns we report are remarkably consistent for four different trophic groups (producers, herbivores, detritivores and predators) and two major ecosystem types (aquatic and terrestrial). Collectively, our analyses suggest that the average species loss does indeed affect the functioning of a wide variety of organisms and ecosystems, but the magnitude of these effects is ultimately determined by the identity of species that are going extinct.