生态阈值:概念、方法与研究展望

生态阈值概念是20世纪70年代提出的,主要指生态系统的几个稳态之间突然改变的点或区域。在阐明生态系统结构与功能的关系、构建区域可持续发展范式以及服务于生态系统管理和生态红线的划定中,生态阈值的检测和量化有着重要的理论和实践意义。该文首先梳理了前人关于生态阈值的概念、类型的一些提法,从预警研究角度提出可以从两个层次理解生态阈值概念:生态阈值点是系统从量变到质变的转折点,类似于红色界限;而生态阈值带可以理解为量变过程中不同稳态之间的转换区域,类似于黄色与橙色预警边界带。黄色生态阈值表示生态系统可通过自身的调节能力重新达到稳定状态;橙色生态阈值表示需要排除干扰因子使得生态系统重新达到平衡;而红色生态阈值为关键阈值点,超过此阈值,生态系统将发生不可逆的退化甚至崩溃。该文还总结了目前确定生态阈值的主要方法,主要是基于野外观测数据的统计分析与模型模拟方法。最后,基于生态系统服务、生物多样性保护与生态系统管理等几个当今生态学热点研究领域,简单总结归纳了生态阈值的研究现状,并提出生态阈值未来的3个研究难点和方向:1)开展针对生态阈值检测和量化的研究;2)关注生态阈值的尺度效应并加强野外观测;3)发挥生态阈值的预警作用,指导"生态红线"的划定和生态系统管理。     

生态系统稳定性定义剖析

生态系统稳定性是理论生态学的焦点问题之一 ,综述和剖析生态系统稳定性的定义 ,对已有的定义进行了改进。生态系统稳定性是不超过生态阈值的生态系统的敏感性和恢复力。在这个概念中涉及到 3个概念 :生态阈值、敏感性和恢复力 ,阈值是生态系统在改变为另一个退化 (或进化 )系统前所能承受的干扰限度 ;敏感性是生态系统受到干扰后变化的大小和与其维持原有状态的时间 ;退化生态系统的恢复力就是消除干扰后生态系统能回到原有状态的能力 ,包括恢复速度和与原有状态的相似程度。在保护生态学中 ,阈值与恢复力的定义具有广泛的应用 ,特别是生态系统受到负面的干扰后而退化 ,退化的生态系统逐步恢复的过程可以利用恢复力来测定 ;而保护的成果就是力图避免干扰超过系统的阈值而达到一个实际的演替     

生态阈值确定方法综述

生态系统在环境条件变化时表现出的剧变或阈值现象是当前生态学研究的热点,但是生态阈值定量检测的困难阻碍了这一主题的研究与应用。本文从典型案例入手,通过分析潜在生态阈值的S型曲线式、补给-压力式和跃迁式驱动-响应机理,归纳了局部加权回归散点平滑法、分段回归、高斯模型、拐点分析软件、稳态转换检测软件、指示种阈值分析和系统动力学仿真模型7种生态阈值确定方法,并评述了其优缺点和适用性,以期为生态阈值的定量分析研究提供方法借鉴。     

基于无人机影像的阿拉善东南部荒漠灌丛植被空间格局研究

干旱区灌丛植被空间格局受多种物理和生态过程影响，能够指示生态系统的状态。研究通过量化灌丛斑块大小的空间分布来评估阿拉善高原东南部覆沙荒漠植被生态系统的状态，采用点格局分析法分析灌木种群的相互关系，以阐明不同灌木种在斑块格局形成中的作用，并结合土壤条件及下垫面粗糙度等指标验证评估的准确性，探讨灌丛空间格局差异的内在机理。结果表明，研究区样方2灌丛斑块大小符合截尾幂律分布，其他样方符合对数正态分布，前者的空间结构及生境条件均优于后者，说明植被空间格局可以准确表征生态系统状态。在局地尺度上灌木种内和种间呈现不同的相互关系，以竞争关系为主导是导致斑块破碎化的主要驱动机制。小灌木（如猫头刺）的种内互利关系有利于促进多样化斑块形态的形成，而大灌木（如沙冬青和蒙古扁桃）种间的互利作用则有利于形成异质性更强的复杂空间格局。基于灌丛斑块的空间格局评估生态系统状态，可为保护和恢复生态脆弱区受损植被提供重要的借鉴。     

大堤型湖滨带生态系统健康状态驱动因子——以太湖为例

湖滨带是湖泊生态系统的重要组成部分,对维持湖泊生态系统健康和改善水环境功能具有积极作用。由于防洪需要,我国许多湖泊在湖滨带中修建了防洪大堤,防洪大堤对湖滨带生态系统的影响还缺乏研究,识别引起大堤型湖滨带生态健康退化的驱动因子是开展湖滨带生态修复的必要前提。针对太湖湖滨带的特点,在定性筛选了太湖主体营养状态、入湖河流污染负荷通量、岸带类型、风浪强度4个主要影响因子的基础上,分别采用"多元线性逐步回归法"和"偏相关系数法"进行驱动因子识别,2种方法确定的驱动因子个数均为3个,且3者的驱动力大小排序也相同,即太湖主体营养状态>岸带类型>入湖河流污染负荷通量。3个驱动因子对太湖湖滨带生态系统健康的影响均为负效应,也即太湖主体的营养状态综合指数越高、入湖河流污染负荷通量越重、岸带状况越差,湖滨带生态系统也就越不健康。另外,从统计方法的角度解释了"风浪强度"没有入选为驱动因子的原因;澄清了现阶段环境学、生态学领域对"驱动因子"识别方法的误解及不足之处。研究结果为大堤型湖滨带的生态修复方案提供了理论支持。     

消落带生态系统氮素截留转化的主要机制及影响因素

消落带是陆地与水体(河流、湖泊、水库、湿地以及其他特殊水体)之间的生态过渡带,具有独特的生态水文学和生物地球化学过程,是截留和转化NH₄⁺、NO₃^-等非点源氮素进入水体的最后一道生态屏障.整合已有相关研究成果发现: 1)植物固持作用改变氮素在土壤-植被-土壤-大气中相对存在位置;2)微生物反硝化作用将氮素从系统内永久性地去除,是消落带生态系统氮素截留转化的主要机制,但其相对贡献率仍有很大的不确定性.在不同流域背景条件下,影响消落带生态系统氮素生物地球化学循环的主要生态因子变化较大,很难确定地下水位高低、植被状况、微生物属性和土壤基质等哪一个生态因子是驱动消落带生态系统氮素循环的关键因子.研究方法的局限性、大的时空尺度数据的缺乏及对植被宽度认识的模糊性,是导致消落带生态系统氮素截留转化结果变异性大的主要原因.因此,应在消落带生态系统具体研究区位环境因子基础上,利用数学模型、GIS、RS等分析方法及同位素示踪和气体联用测定等定量分析技术,从不同时空尺度研究消落带生态系统氮素的循环与转化规律,以实现消落带生态系统氮素截留转化最优化,为消落带生态系统的科学管理提供理论基础.     

我国生态系统生态阈值研究基础

生态系统中广泛存在非线性变化,表现为系统状态随着压力的逐渐增加而发生骤然转变。为解释这种变化,国外生态学家提出了生态阈值和稳态转换的概念,不断完善理论和方法体系,开展机理和案例研究,深化对复杂系统演化机制的理解,并开始应用于环境管理。在我国,近几十年来在各类生态系统中开展了大量关于压力-响应的定量化研究,取得了丰富成果。这些研究在本质上与生态阈值和稳态转换理论范式紧密关联。本文以“中国生态阈值和稳态转换案例数据库”为基础,按照河流、湖泊、湿地、森林、草地、河口与海洋、农田、荒漠、城市、冻原10种生态系统类型,筛选归纳了相关生态阈值,并阐释了稳态转换机理。将研究案例与生态阈值、稳态转换理论范式进行衔接,目的是整合多领域研究成果,作为生态系统复杂性研究的基础,推动其在生态环境监测、生态安全预警以及生态标准创新发展领域中的应用。     

东北粮食主产区农业生态系统健康格局与因子诊断——以吉林省为例

运用生态系统健康的理论与方法研究粮食主产区农业生态系统健康问题具有重要的意义,以东北粮食主产区的典型区域吉林省为研究对象,基于构建的胁迫-状态-免疫(S-S-I)与活力-结构组织-恢复力(V-O-R)农业生态系统健康评价指标体系,运用最优组合赋权法、综合评价模型、GIS空间分析技术和灰色斜率相似关联度诊断模型对2000—2011年吉林省农业生态系统健康的时空格局以及影响因子进行分析.结果表明: 时间特征上,2000—2011年吉林省农业生态健康等级从“不健康级”状态向“较健康级”状态转变,农业生态系统健康水平正逐步提高.空间特征上,2000—2011年吉林省农业生态系统健康状况空间差异日益显著,中部地区的农业生态健康水平保持不变,东南部与西部正逐渐提高.吉林省农业生态系统健康水平提高的主要贡献因子是经济驱动、环境治理与社会发展,主要障碍因子是生态压力、组织结构与投入能力等.最后,提出相关措施进一步改善区域农业生态系统健康状况.     

国土生态空间中现存建设用地与耕地退出的生态系统服务响应——以昆山市为例

如何管控包括生态保护红线等国土重要生态空间中的存量建设用地和耕地，是目前业界争论的焦点问题，而是否该退出、怎么退出、有何影响，则是值得学界重点探讨的科学问题。以昆山市为例，基于"生态系统服务重要性-生态敏感性-景观连通性"框架识别其国土重要生态空间，在分析重要生态空间与其现存建设用地、耕地的冲突特征及影响因素基础上，多情景模拟并评估重要生态空间中耕地和建设用地不同退出方式下的区域生态系统服务响应特征。研究表明：（1）占全域不足1/4的重要生态空间中，现存耕地和建设用地主要分布在水域周边，且以耕地占用冲突为主。（2）重要生态空间中耕地和建设用地退出方式不同会导致不同的生态系统服务响应特征，整体上生态保护情景能够有效地缓解服务间的权衡关系，但过度生态保护并不是最合适的；需权衡好不同国家既有政策之间关系，在保护中要避免"一刀切"问题。此外，研究尝试探讨了重要生态空间中现存用地斑块退出的生态系统服务响应研究的方法和思路，未来还可就围绕退出斑块的面积阈值、空间配置特征及其生态系统服务响应规律展开深化研究。     

生态脆弱区生态系统状态演变分析的若干数学方法

生态脆弱区往往存在多个生态系统(草原、荒漠和灌木等)共存的现象.由于外部环境和人类活动等因素的影响,生态脆弱区会发生从一种生态系统转变为另一种生态系统的现象,即突变现象.分析生态脆弱区多生态系统共存情况下生态系统的稳定性对了解生态脆弱区生态系统的变化具有重要意义.本文回顾了目前能够描述生态脆弱区多生态系统的动力系统及其...     

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.     

Ecological thresholds: Concept,Methods and research outlooks

The concept of ecological thresholds was raised in the 1970s. However, it was subsequently given different definitions and interpretations depending on research fields or disciplines. For most scientists, ecological thresholds refer to the points or zones that link abrupt changes between alternative stable states of an ecosystem. The measurement and quantification of ecological thresholds have great theoretical and practical significance in ecological research for clarifying the structure and function of ecosystems, for planning sustainable development modes, and for delimiting ecological red lines in managing the ecosystems of a region. By reviewing the existing concepts and classifications of ecological thresholds, we propose a new concept and definition at two different levels: the ecological threshold points, i.e. the turning points of quantitative changes to qualitative changes, which can be considered as ecological red lines; the ecological threshold zones, i.e. the regime shifts of the quantitative changes among different stable states, which can be considered as the yellow and/or orange warning boundaries of the gradual ecological changes. The yellow thresholds mean that an ecosystem can return to a stable state by its self-adjustment, the orange thresholds indicate that the ecosystem will stay in the equilibrium state after interference factors being removed, whereas the red thresholds, as the critical threshold points, indicate that the ecosystem will undergo irreversible degradation or even collapse beyond those points. We also summarizes two types of popular Methods in determining ecological thresholds: statistical analysis and modeling based on data of field observations. The applications of ecological thresholds in ecosystem service, biodiversity conservation and ecosystem management research are also reviewed. Future research on ecological thresholds should focus on the following aspects: (1) methodological development for measurement and quantification of ecological thresholds; (2) emphasizing the scaling effect of ecological thresholds and establishment of national-scale observation system and network; and (3) implementation of ecological thresholds as early warning tools in ecosystem management and delimiting ecological red lines.     

典型红壤区自然生态修复的适用性

自然修复主要通过封山育林、禁止农作、禁牧禁伐措施,减少人类对环境的扰动,利用自然生态环境的自我演替能力,恢复生态环境,实现生态平衡。自然修复作为一种成本低、无污染的生态修复手段很早就受到人们重视,但关于自然修复适用范围的研究较少。为了正确认识自然修复的适用性,选择了我国南方红壤地区长期遭受严重土壤侵蚀危害的福建省长汀县为研究对象,通过对长期自然修复样地的监测资料分析,发现在坡度条件为20%—30%下,当植被覆盖度低于20%的退化阈值时,严重的土壤侵蚀引发的土壤肥力损失将导致生态系统自我退化,自然修复不仅无法改善当地的生态系统,反而会引起生态系统的进一步恶化。由此可见,自然修复并不适合所有的生态系统,当生态系统退化到一定程度时,退化生态系统必须通过人工干预来修复。因此,必须探索适合当地的生态修复模式,在生态系统退化突破阈值时,红壤丘陵区应通过恢复土壤肥力、促进自然植被覆盖度增加、综合提高生态系统健康水平。     

Modelling climate‐change‐induced nonlinear thresholds in cephalopod population dynamics

A significant global challenge lies in our current inability to anticipate, and therefore prepare for, critical ecological thresholds (i.e. tipping points in ecosystems). This deficit stems largely from an inadequate understanding of the many complex interactions between species and the environment at the ecosystem level, and the paucity of mechanistic models relating environment to population dynamics at the species level. In marine ecosystems, abundant, short‐lived and fast‐growing species such as anchovies or squids, consistently function as ‘keystone’ groups whose population dynamics affect entire ecosystems. Increasing exploitation coupled with climate change impacts has the potential to affect these ecological groups and consequently, the entire marine ecosystem. There are currently very few models that predict the impact of climate change on these keystone groups. Here we use a combination of individual‐based bioenergetics and stage‐structured population models to characterize the fundamental capacity of cephalopods to respond to climate change. We demonstrate the potential for, and mechanisms behind, two unfavourable climate‐change‐induced thresholds in future population dynamics. Although one threshold was the direct consequence of a decrease in incubation time caused by ocean warming, the other threshold was linked to survivorship, implying the possibility of management through a modification of fishing mortality. Additional substantive changes in phenology were also predicted, with a possible loss in population resilience. Our results demonstrate the feasibility of predicting complex nonlinear dynamics with a reasonably simplistic mechanistic model, and highlight the necessity of developing such approaches for other species if attempts to moderate the impact of climate change on natural resources are to be effective.     

Embracing thresholds for better environmental management

Three decades of study have revealed dozens of examples in which natural systems have crossed biophysical thresholds (‘tipping points’)—nonlinear changes in ecosystem structure and function—as a result of human-induced stressors, dramatically altering ecosystem function and services. Environmental management that avoids such thresholds could prevent severe social, economic and environmental impacts. Here, we review management measures implemented in ecological systems that have thresholds. Using Ostrom''s social–ecological systems framework, we analysed key biophysical and institutional factors associated with 51 social–ecological systems and associated management regimes, and related these to management success defined by ecological outcomes. We categorized cases as instances of prospective or retrospective management, based upon whether management aimed to avoid a threshold or to restore systems that have crossed a threshold. We find that smaller systems are more amenable to threshold-based management, that routine monitoring is associated with successful avoidance of thresholds and recovery after thresholds have been crossed, and that success is associated with the explicit threshold-based management. These findings are powerful evidence for the policy relevance of information on ecological thresholds across a wide range of ecosystems.     

The concept of threshold and its potential application to landscape planning

The concept of threshold can potentially be applied to conservation planning of species, habitats, and ecosystems. It also has significance in managing social–ecological systems for resilience. However, our understanding and use of threshold has been scattered among various disciplines, and the link to conservation planning and social–ecological system management has not been strongly established. The review of the use of threshold in various disciplines reveals that the term is used in a similar manner in both natural and social sciences: a threshold is a point or a zone on an independent variable, and if it is crossed, a sudden, large change in the state of a dependent variable occurs. Even a small change in the independent variable brings this drastic change; nonlinear relationship characterizes the threshold response. Thresholds also separate alternative regimes in a social–ecological system. The discussion of the application of threshold concept to watershed planning concludes that although using one threshold value of impervious surfaces in a watershed to regulate new developments and retrofit old ones is a cost-effective method, a more integrated approach is needed. The use of habitat amount threshold to conserve species promotes proactive planning that would prioritize areas for protection before the threshold is reached and would restore habitat based on the threshold target. However, species-specific data to decide on the threshold is often lacking, and the identification of thresholds is not straightforward. Nonetheless, the concept of threshold is appealing for proactive planning and significant in managing social–ecological systems for resilience.     

Perspectives for ecosystem management based on ecosystem resilience and ecological thresholds against multiple and stochastic disturbances

Ecosystem resilience is the inherent ability to absorb various disturbances and reorganize while undergoing state changes to maintain critical functions. When ecosystem resilience is sufficiently degraded by disturbances, ecosystem is exposed at high risk of shifting from a desirable state to an undesirable state. Ecological thresholds represent the points where even small changes in environmental conditions associated with disturbances lead to switch between ecosystem states. There is a growing body of empirical evidence for such state transitions caused by anthropogenic disturbances in a variety of ecosystems. However, fewer studies addressed the interaction of anthropogenic and natural disturbances that often force an ecosystem to cross a threshold which an anthropogenic disturbance or a natural disturbance alone would not have achieved. This fact highlights how little is known about ecosystem dynamics under uncertainties around multiple and stochastic disturbances. Here, we present two perspectives for providing a predictive scientific basis to the management and conservation of ecosystems against multiple and stochastic disturbances. The first is management of predictable anthropogenic disturbances to maintain a sufficient level of biodiversity for ensuring ecosystem resilience (i.e., resilience-based management). Several biological diversity elements appear to confer ecosystem resilience, such as functional redundancy, response diversity, a dominant species, a foundation species, or a keystone species. The greatest research challenge is to identify key elements of biodiversity conferring ecosystem resilience for each context and to examine how we can manage and conserve them. The second is the identification of ecological thresholds along existing or experimental disturbance gradients. This will facilitate the development of indicators of proximity to thresholds as well as the understanding of threshold mechanisms. The implementation of forewarning indicators will be critical particularly when resilience-based management fails. The ability to detect an ecological threshold along disturbance gradients should therefore be essential to establish a backstop for preventing the threshold from being crossed. These perspectives can take us beyond simply invoking the precautionary principle of conserving biodiversity to a predictive science that informs practical solutions to cope with uncertainties and ecological surprises in a changing world.     

Two models of evolution in Ganarian lizards based on the use of spatial resources

The morphological and genetic differences between populations of Canarian lizards on four islands were analysed in relation to two ecological systems: the laurisilva forest and the young volcanic ecosystems or 'malpaises'. The two ecosystems induce two different evolutionary responses by lizard populations; morphological and genetic modifications are intense in the case of a very old ecosystem like laurisilva whereas in the young volcanic ecosystems, morphological modifications are much more pronounced although the temporary nature of the ecosystem is limiting from point of view of speciation.     

Light‐driven tipping points in polar ecosystems

Some ecosystems can undergo abrupt transformation in response to relatively small environmental change. Identifying imminent ‘tipping points’ is crucial for biodiversity conservation, particularly in the face of climate change. Here, we describe a tipping point mechanism likely to induce widespread regime shifts in polar ecosystems. Seasonal snow and ice‐cover periodically block sunlight reaching polar ecosystems, but the effect of this on annual light depends critically on the timing of cover within the annual solar cycle. At high latitudes, sunlight is strongly seasonal, and ice‐free days around the summer solstice receive orders of magnitude more light than those in winter. Early melt that brings the date of ice‐loss closer to midsummer will cause an exponential increase in the amount of sunlight reaching some ecosystems per year. This is likely to drive ecological tipping points in which primary producers (plants and algae) flourish and out‐compete dark‐adapted communities. We demonstrate this principle on Antarctic shallow seabed ecosystems, which our data suggest are sensitive to small changes in the timing of sea‐ice loss. Algae respond to light thresholds that are easily exceeded by a slight reduction in sea‐ice duration. Earlier sea‐ice loss is likely to cause extensive regime shifts in which endemic shallow‐water invertebrate communities are replaced by algae, reducing coastal biodiversity and fundamentally changing ecosystem functioning. Modeling shows that recent changes in ice and snow cover have already transformed annual light budgets in large areas of the Arctic and Antarctic, and both aquatic and terrestrial ecosystems are likely to experience further significant change in light. The interaction between ice‐loss and solar irradiance renders polar ecosystems acutely vulnerable to abrupt ecosystem change, as light‐driven tipping points are readily breached by relatively slight shifts in the timing of snow and ice‐loss.     

Multiple stressors,nonlinear effects and the implications of climate change impacts on marine coastal ecosystems

Global climate change will undoubtedly be a pressure on coastal marine ecosystems, affecting not only species distributions and physiology but also ecosystem functioning. In the coastal zone, the environmental variables that may drive ecological responses to climate change include temperature, wave energy, upwelling events and freshwater inputs, and all act and interact at a variety of spatial and temporal scales. To date, we have a poor understanding of how climate‐related environmental changes may affect coastal marine ecosystems or which environmental variables are likely to produce priority effects. Here we use time series data (17 years) of coastal benthic macrofauna to investigate responses to a range of climate‐influenced variables including sea‐surface temperature, southern oscillation indices (SOI, Z4), wind‐wave exposure, freshwater inputs and rainfall. We investigate responses from the abundances of individual species to abundances of functional traits and test whether species that are near the edge of their tolerance to another stressor (in this case sedimentation) may exhibit stronger responses. The responses we observed were all nonlinear and some exhibited thresholds. While temperature was most frequently an important predictor, wave exposure and ENSO‐related variables were also frequently important and most ecological variables responded to interactions between environmental variables. There were also indications that species sensitive to another stressor responded more strongly to weaker climate‐related environmental change at the stressed site than the unstressed site. The observed interactions between climate variables, effects on key species or functional traits, and synergistic effects of additional anthropogenic stressors have important implications for understanding and predicting the ecological consequences of climate change to coastal ecosystems.