Evolutionary basis and ecological role of toxic microbial secondary metabolites

This presentation develops a theory of the evolutionary origin and ecological implications of toxic microbial secondary metabolites. The theory is based on a model system that outlines cause—effect associations between pertinent biotypes in the aflatoxin contamination of developing maize kernels. The model suggests that the aflatoxin-producing fungi are natural digestive tract inhabitants of a number of insect species that feed on developing kernels. During feeding, the insect larvae introduce fungal propagules and provide infection sites on damaged kernels. The fungal association with insects exhibits extraordinary variability, ranging from symbiotic to pathogenic. Elaboration of aflatoxin by the fungus facilitates the pathogenic process in host insects. The theory contends that genetic information for secondary microbial metabolites evolved during ecosystem disequilibria. During periods of ecological stability, mechanisms evolved for repression of toxic secondary metabolite biosynthesis. The theory broadly suggests that contemporary agricultural activities presents the requisite milieu for production or toxic microbial secondary metabolites.     

Ecological Thresholds: The Key to Successful Environmental Management or an Important Concept with No Practical Application?

An ecological threshold is the point at which there is an abrupt change in an ecosystem quality, property or phenomenon, or where small changes in an environmental driver produce large responses in the ecosystem. Analysis of thresholds is complicated by nonlinear dynamics and by multiple factor controls that operate at diverse spatial and temporal scales. These complexities have challenged the use and utility of threshold concepts in environmental management despite great concern about preventing dramatic state changes in valued ecosystems, the need for determining critical pollutant loads and the ubiquity of other threshold-based environmental problems. In this paper we define the scope of the thresholds concept in ecological science and discuss methods for identifying and investigating thresholds using a variety of examples from terrestrial and aquatic environments, at ecosystem, landscape and regional scales. We end with a discussion of key research needs in this area.     

Motivation and Benefits of Complex Systems Approaches in Ecology

Studies of complex systems in other disciplines provide models and analytical strategies for understanding ecosystems and landscapes. The emphasis is on invariant properties, particularly processes that create scaling relations over wide ranges of scale, both in time and space. Translations between levels of ecological organization may be accomplished by succinct characterizations of processes that operate at fine scales, followed by renormalization group analysis to reveal patterns at broad scales. The self-organized patterns found in simple ecosystem, landscape, and forest-fire models may be explained as feedback between the system state and control parameters. Critical phenomena and phase transitions are expected in open, dissipative systems where long-range correlations defy predictions based on average population densities, a concept that becomes irrelevant as nonstationary conditions prevail. Thus, complexity theory for open systems relates to the ecology of self-entailing ecosystems that function as their own environments and thereby create constraints through emergence. Received: 14 April 1998; accepted 26 May 1998     

西双版纳地区不同胶农(林)复合系统的植物水分利用效率比较

当前,西双版纳地区大面积橡胶单一种植林已引发了诸多的生态环境问题,为解决这些问题同时协调当地的经济发展,农林复合系统被生态学者们认为是最好的解决办法。然而目前关于不同间作模式下橡胶树水分利用效率研究还很少。因此,于2013－2014年的雨季中期(8月)和末期(11月)、雾凉季(1月)、干热季(3月),分别测定了中国科学院西双版纳热带植物园内四种不同胶农(林)复合系统(橡胶—叶茶、橡胶—咖啡、橡胶—大叶千斤拔、橡胶—可可复合系统)及单层橡胶林的土壤含水量、橡胶树及其林下间作植物的枝条凌晨水势和正午水势,以及它们植物叶片的δ13 C值,分析了各胶农(林)复合系统内橡胶树的水分利用效率,以期遴选出水分关系配置合理的复合橡胶林栽培模式,为环境友好型橡胶种植林的建设和推广提供相关的参考依据和理论支持。结果表明：除橡胶—可可复合系统以外,其余胶农(林)复合系统内的橡胶树水分利用效率值均高于单层橡胶林;橡胶—大叶千斤拔复合系统的土壤含水量显著高于其它复合系统;橡胶—叶茶复合系统的土壤含水量虽然低于橡胶—大叶千斤拔复合系统,但其最为稳定、季节变化小;橡胶—咖啡复合系统的水分利用效率最高最稳定,即使受到寒害也没有引起明显变化;而橡胶—可可复合系统的作用不明显,所有特征都与单层橡胶林相似。这表明除了橡胶—可可复合系统外,其他3种胶农(林)复合系统都显著地缓解了橡胶树在旱季所遭受的水分胁迫,同时也能有效地抵御突发性天气灾害。     

Sustainable ecosystem management using optimal control theory: part 1 (deterministic systems)

The concept of sustainability, an abstract one by its nature, has been given a mathematical representation through the use of Fisher information as a measure. It is used to propose the sustainability hypotheses for dynamical systems, which has paved the way to achieve sustainable development through externally enforced control schemes. For natural systems, this refers to the task of ecosystem management, which is complicated due the lack of clear objectives. This work attempts to incorporate the idea of sustainability in ecosystem management. The natural regulation of ecosystems suggests two possible control options, top-down control and bottom-up control. A comparison of these two control philosophies is made on generic food chain models using the objectives derived from the sustainability hypotheses. Optimal control theory is used to derive the control profiles to handle the complex nature of the models and the objectives. The results indicate a strong relationship between the hypotheses and the dynamic behavior of the models, supporting the use of Fisher information as a measure. As regards to ecosystem management, it has been observed that top-down control is more aggressive but can result in instability, while bottom-up control is guaranteed to give a stable and improved dynamic response. The results also indicate that bottom-up control is a better option to affect shifts in the dynamic regimes of a system, which may be required to recover the system from a natural disaster like the hurricane Katrina.     

耗散结构理论与农田杂草系统控制策略初探

一、农田杂草系统控制与耗散结构理论耗散结构理论阐明了一个开放系统由混沌无序向有序态进化的过程和规律。生态系统属耗散结构已得到论证。作为农田生态系统,在开放性、非平衡性、相干性和随机涨落机制四方面,与自然生态系统相似,均满足耗散结构的构成条件,因此,农田生态系统也属耗散结构。农田杂草防除实质上是农田生态系统的调     

生态系统多稳态研究进展

在多稳态的生态系统中,外力可能导致生态系统状态突然之间发生不可逆转的转变,从而达到一个新的平衡状态。但目前对多稳态理论的系统研究很少,如何使用预警信号来预测生态系统的状态转变依旧是个难题。通过多稳态理论的梳理提出了一个更加综合的多稳态定义,并以放牧模型为例,系统总结了多稳态理论的相关概念,将多稳态理论应用在生态系统演替和扰沌理论的解释中;通过对生态系统稳态转换预警信号的原理、优缺点和应用条件的分析,对不同尺度下多稳态的研究方法进行了归纳;最后提出了目前多稳态领域的研究问题和未来的研究重点。结果表明:(1)将时间和空间预警信号结合在一起,并量化正确预警信号的概率,对错误预警信号的比例进行加权,可能会提供更准确的稳态转换的预报。(2)定量观测试验适用于小尺度的研究,而较大尺度的研究则采用简化的模型来模拟研究,选择正确的尺度极有可能改变预警信号的可靠性。(3)结合多稳态理论研究生态系统临界转换和反馈控制机制,并将基于性状的特征指标和进化动力学纳入其中,是生态系统修复实践的重要研究方向。(4)将多稳态相关理论和生态保护管理政策的实践相结合,是多稳态理论未来应用的前景。本研究为多稳态理论和实践的...     

Closed-loop learning control of bio-networks.

A general goal of systems biology is to acquire a detailed quantitative understanding of the life-sustaining interactions between genes and proteins. There arises an interesting question of whether these network dynamics can be controlled externally. In the open-loop approach to experimental biology, a control design would be chosen based on a desired target response and modeling with all the available knowledge about the system. If the system is not completely understood or disturbances occur, then unexpected deviations from the desired response can arise. A means to circumvent this difficulty is to optimize the controls in a closed-loop operation by modifying successive input controls based on the performance of previous controls. This paper presents a simulation of closed-loop learning control applied to biological systems in order to generate a desired response. The most powerful advantage of this technique is that the controls are deduced based on experimental results and the process can operate without a model for the underlying biochemical network. This feature eliminates the problem of faulty predictions as well as the need for a detailed understanding of the underlying molecular pathways, suggesting that biological systems can be controlled even before the post-systems biology era.     

How Regime Shifts in Connected Aquatic Ecosystems Are Affected by the Typical Downstream Increase of Water Flow

All over the world freshwater ecosystems like ponds, ditches and lakes suffer from nutrient-driven regime shifts from submerged plants to dominance by algae or free-floating plants. Although freshwaters are often connected and part of a network, most of our current knowledge on regime shifts comes from studies of isolated ecosystems. The few studies that have assessed the spatial manifestation of regime shifts overlooked the hydrological fact that the water flow through connected waters typically increases in the downstream direction. Here, we use a complex ecosystem model to show that this increase in flow does not lead to spatial differences in ecosystem state. We support these findings with a simple, analytically tractable, nutrient retention model on connected waterbodies. The model shows that all bodies have the same nutrient concentration despite spatial gradients in the flow of water as well as nutrients carried by the water. As a consequence, each connected waterbody is equally vulnerable to a regime shift, implying a regime shift to be system-wide. Furthermore, it appeared that each connected waterbody behaves the same as an isolated waterbody, implying that the vast body of theory on isolated systems, like alternative stable states theory, can still be useful for connected systems. Although these findings are violated when there is heterogeneity in lateral runoff or waterbody characteristics—leading to spatial differences in ecosystem state and therefore to differences in the vulnerability to a regime shift—they show that the typical downstream build-up of water flow does not necessarily lead to differences in ecological state, and thereby provide a basic concept to better understand the ecology of connected freshwaters.     

Advancing Ecosystem Science by Promoting Greater Use of Theory and Multiple Research Approaches in Graduate Education

Since the inaugural edition of Ecosystems was published in 1998, ecosystem science has undergone substantial changes including the development of new research methods and an increasing emphasis on collaborations across traditional academic boundaries. In response to this transformation, we reflect on the current state of theory in ecosystem science, and make recommendations for training the next generation of Ph.D.-level ecosystem scientists. Specifically, we call for increased integration of theory into ecosystem science and outline the utility of iterating between theory and data generated by observations, experiments, and quantitative models. We recommend exposing graduate students to these three major approaches for generating data and propose strategies that students, advisors, and departments can employ to ensure this exposure. Ultimately, a successful training program will provide students with an understanding of key theories related to ecosystem science and how they interact with data, an appreciation for the interconnectedness of approaches to scientific inference, and a well-developed skill set in at least one approach—thereby empowering them to confidently tackle our pressing environmental problems. Although this is a daunting list of goals, continuing to advance our understanding of how ecosystems function necessitates a rigorous and well-developed training program.     

食物链长度理论研究进展

食物链长度（Food chain length,FCL）是生态系统中最重要的特点之一,它通过改变生物间的营养关系,影响着生物多样性,群落的结构以及稳定性;它是反映食物网物质转换与能量传递的综合指数,食物链及其动态特征是生态学许多重要理论的基础,食物链长度理论的研究进展,推动了人们对水域生态系统中生物和非生物相互作用的理解。回顾了食物链长度的3种度量方法及其详细的计算方法,在此基础上简述了各方法的特点。综述了食物链长度的决定因素的4种假说（资源可利用性假说、生产力空间假说、生态系统大小假说、动态稳定性假说）及其交互作用,重点总结了湖泊食物链长度的空间格局与决定因素的研究进展。最后,食物链长度研究展望,包括食物链长度决定因子研究存在的问题及发展方向的总结,以及在在水域生态学中的应用的研究进展,例如食物链长度在指示污染物的生物富集中的研究进展、食物链食物链长度在指导生物操作、以及在食物链长度在对气候变化响应方面的研究进展等等。     

一类生态系统的脉冲控制

利用脉冲系统的线性近似判定的方法对一个具有脉冲控制的生物模型进行研究,得到了使其渐近稳定到原先不稳定的平衡点的充要条件并给出了生态解释。     

基于“生态系统服务网”理论的国土空间规划研究

生态环境恶化使国土空间的管理从重视开发到重视保护转变,相应的思想体系、理论体系与管理机制需要打破旧的路径依赖,建立新的国土空间规划体系。生态系统服务网理论将生态系统服务供给与需求融合到一起,推动生态系统服务"一张网"与国土空间规划"一张图"的衔接。（1）生态系统服务网的网络属性诠释了山水林田湖草-人生命共同体思想体系;（2）生态系统服务网理论强调供给与需求的有效匹配与融合,是国土空间规划的重要依据;（3）生态系统服务网的尺度特征与国土空间规划层级体系存在对应关系,有助于规划的传导与实施;（4）生态系统服务网中供给能力和空间需求匹配的评价是"双评价"的主要内容,为"三区三线"的划定与落地提供了依据;（5）生态系统服务网的价值评估、空间制图与优化,为确定国土空间开发边界与规模奠定了基础,为两山转化路径提供思路和依据,可有效促进国土空间的高质量开发利用。     

粤港澳大湾区水生态修复及展望

水是生态系统物质循环和能量流动的重要纽带,水生态系统修复在区域生态系统修复中起到关键作用。粤港澳大湾区剧烈人类活动对江河湖库生态系统造成破坏和干扰,江河湖库污染严重,水生物减少,导致流域水生态服务功能退化甚至丧失;从生态修复科学内涵出发,判断湾区水生态系统健康状况已处于非生物控制跃迁阈值之下;针对该形势,从工程建设、水环境治理、空间规划和管理机制四个方面,梳理湾区近期开展的与水生态修复相关的水生态文明建设、水污染防治行动计划、水生态空间划定和推进河长制等工作,并对其中用到的技术、指标和制度进行条理;然后以茅洲河流域综合治理和广东万里碧道作为水生态修复的点、面代表,从水生态修复的整体目标、采用的技术措施、效果评价的指标体系和管理制度方法等方面分析当前的工作现状;总结湾区现状水生态修复工作,认为湾区水生态系统的非生物修复阶段基本结束;基于生态系统修复理论结合湾区江河湖库生态系统特点,提出适合湾区的水生态修复框架,讨论水生态系统修复面临的问题和未来工作的展望,为大湾区水生态修复提供直接依据。     

基于能值理论的循环复合农业生态系统发展评价——以福建省福清星源循环农业产业示范基地为例

循环农业是当前农业可持续发展理念的具体运作模式。对能值分析方法优化,使其更适合循环复合生态系统的应用上进行优化,并以福建省福清星源循环农业产业示范基地为例验证,评价复合生态系统的可持续发展程度和经济效益。结果表明改进的能值分析方法对循环复合农业生态系统的可持续发展评价更科学,复合系统的可持续发展指数比单纯的生猪养殖提高23.44%—33.86%,在4种组合的循环模式中以"生猪养殖-沼气工程-有机肥生产-种植业"循环复合生态系统整体效益最佳,其可持续发展指数最高,环境负载率最低,净能值产出率仅略低于"生猪养殖-沼气工程-种植业"复合系统。     

The Semiglades: The Collision of Restoration,Social Values,and the Ecosystem Concept

Defining success targets in restoration and how social values affect them are two commonly discussed issues in restoration today. We believe that how success is commonly defined—with vague terms such as “healthy ecosystem” or cited as a return to a previous, historic state—needs to be reevaluated. With the increasing number of novel ecosystems, there is an increasing conflict between the ecosystem concept, social values, and restoration. This arises from the fact that ecosystems are defined by the values of the scientists describing them, necessarily constraining the ecosystem to a generally static concept. It is not directly the concept, but how it is perceived through our filter of social values that represses the creativity and innovation needed in restoration today. Within restoration, we feel that the ecosystem concept does a disservice by ignoring the increasing number of novel systems, and that hinders real progress in a time when hesitation can be costly. To best illustrate this, we offer the example of restoration of the Florida Everglades and how it has become a novel system in pattern and process. We suggest renaming the Everglades “The Semiglades” in hopes of opening a dialog to expose social/ecosystem biases and include novel landscapes in management and planning.     

The FliK protein and flagellar hook-length control

The bacterial flagellum is a highly complex prokaryotic organelle. It is the motor that drives bacterial motility, and despite the large amount of energy required to make and operate flagella, motile organisms have a strong adaptive advantage. Flagellar biogenesis is both complex and highly coordinated and it typically involves at least three two-component systems. Part of the flagellum is a type III secretion system, and it is via this structure that flagellar components are exported. The assembly of a flagellum occurs in a number of stages, and the "checkpoint control" protein FliK functions in this process by detecting when the flagellar hook substructure has reached its optimal length. FliK then terminates hook export and assembly and transmits a signal to begin filament export, the final stage in flagellar biosynthesis. As yet the exact mechanism of how FliK achieves this is not known. Here we review what is known of the FliK protein and discuss the evidence for and against the various hypotheses that have been proposed in recent years to explain how FliK controls hook length, FliK as a molecular ruler, the measuring cup theory, the role of the FliK N terminus, the infrequent molecular ruler theory, and the molecular clock theory.     

Would Industrial Ecology Exist without Sustainability in the Background?

Industrial ecology rests historically—even in a short lifetime of 15 years or so—on the metaphorical power of natural ecosystems. Its evolution parallels the rise of concerns over unsustainability, that is, the threats to our world's ability to support human life the emergence of sustainability as a normative goal on a global scale. This article examines the relationships between industrial ecology and sustainability and argues that, in its historical relationship to classical ecology models, the field lacks power to address the full range of goals of sustainability, however defined. The classical ecosystem analogy omits aspects of human social and cultural life central to sustainability. But by moving beyond this model to more recent ecosystem models based on complexity theory, the field can expand its purview to address sustainability more broadly and powerfully. Complexity models of living systems can also ground alternative normative models for sustainability as an emergent property rather than the output of a mechanistic economic model for society's workings.     

生态系统状态跃变的早期预警信号及检测

生态系统在气候变化和土地利用及人类活动等的影响下其状态会由某一稳态转变到另一稳态。由于环境压力的复杂性、非线性、随机性等特征，往往导致状态转变表现为非线性、突变、跃变等特点。准确界定系统状态跃变的拐点或阈值点存在很大的挑战，而捕捉接近临界拐点前的生态系统结构和属性上的变化特征作为早期预警信号是切实可行的。早期预警信号理论经历理论框架构建、方法确立、机理认知等近半个多世纪的探索，已经由最初的通过仅依赖检测临界点恢复力的速率减慢、方差增加、系统自相关增强等统计学信号过度到更加多样化的检测方法，如检测系统组分属性的变化特征，诊断系统组分各属性之间的关系变化，系统组分的性状变化、系统组分网络结构变化等等，并且试图整合多信号提高预警的精确性。利用来自自然生态系统的长时间高密度数据集和空间代替时间的数据集，基于多度及性状信号的早期预警，结合稳定性、临界恢复力的减速、以及统计参数的指示作用对系统跃变进行早期诊断和预警是预测生态学的主旨。早期预警信号的深入研究不仅能够完善已有理论的不足，同时还能够为生态系统的保护和管理提供切实有效的理论指导。     

鸭儿湖污染治理研究

鸭儿湖污染是通过氧化塘系统控制的。氧化塘系统,由四个串联氧化塘组成,总面积为2800亩,塘深3米,当废水量为7万吨/天时停留时间为80天。并利用净化后的废水培育鱼种(鱼种塘),通过菌—藻—浮游动物—鱼的相互作用,以鱼种形式回收部分营养元素。以解决在氧化塘沿岸的东西排灌渠12.8公里两岸人民的灌溉水和饮用水的污染问题。从1976年底氧化塘初步建成,四年运转结果表明:COD、有机磷、对硝基酚、对硫磷、马拉硫磷、乐果和六六六处理效果分别为77.3、82.5、99.3、98.7、98.4、92.9和86.2%。每天实际废水负荷为8万吨。1977年以来水生态系逐渐得到恢复,至1979年鱼的畸型率下降到0.1%。鱼体内(背肌)六六六残留从15—30毫克/公斤下降到0.155毫克/公斤,农作物中六六六的残留1979年比氧化塘建立之前降低了2.7—9.4倍。