Source-sink landscape theory and its ecological significance

Exploring the relatiouships between landscape pattern and ecological processes is the key topic of landscape ecology,for which,a large number of indices as well as landscape pattern analysis model were developed.However,one problem faced by landscape ecologists is that it is hard to link the landscape indices with a specific ecological process.Linking landscape pattern and ecological processes has become a challenge for landscape ecologists."Source" and "sink" are common concepts used in air pollution research,by which the movement direction and pattern of different pollutants in air can be clearly identified.In fact,for any ecological process,the research can be considered as a balance between the source and the sink in space.Thus,the concepts of "source" and "sink" could be implemented to the research of landscape pattern and ecological processes.In this paper,a theory of sourcesink landscape was proposed,which include:(1) In the research of landscape pattern and ecological process,all landscape types can be divided into two groups,"source"landscape and "sink" landscape."Source" landscape contributes positively to the ecological process,while "sink" landscape is unhelpful to the ecological process.(2) Both landscapes are recognized with regard to the specific ecological process."Source" landscape in a target ecological process may change into a "sink"landscape as in another ecological process.Therefore,the ecological process should be determined before "source"or "sink" landscape were defined.(3) The key point to distinguish "source" landscape from "sink" landscape is to quantify the effect of landscape on ecological process.The positive effect is made by "source" landscape,and the negative effect by "sink" landscape.(4) For the same ecological process,the contribution of "source" landscapes may vary,and it is the same to the "sink"landscapes.It is required to determine the weight of each landscape type on ecological processes.(5) The sourcesink principle can be applied to non-point source pollution control,biologic diversity protection,urban heat island effect mitigation,etc.However,the landscape evaluation models need to be calibrated respectively,because different ecological processes correspond with different source-sink landscapes and evaluation models for the different study areas.This theory is helpful to further study landscape pattern and ecological process,and offers a basis for new landscape index design.     

景观生态学的学科前沿与发展战略

根据美国景观生态学2001年年会关于景观生态学的关键议题和研究领域特别专题的讨论,综合16位国际知名专家所发表的关于深化理论、整合协调和方法改进等方面的意见,深入论述了景观生态学的6项关键议题和10个优先研究领域。包括通过景观镶嵌体的生态流,土地利用和土地覆被变化的过程、机制,非线性动态和景观复杂性,尺度转换方法论的发展,景观指标与生态过程,人类活动与景观生态,景观格局的优化,景观保育与可持续性,资料获取与准确性评价。并对构建中国景观生态学的理论框架提出了初步的想法,即发展以格局——过程关系为中心的生态空间理论,以人类活动有序化为中心的景观生态建设理论,以发挥景观多重价值为中心的景观规划理论。     

Haplotype Diversity in “Source-Sink” Dynamics of <Emphasis Type="Italic">Escherichia coli</Emphasis> Urovirulence

FimH, the mannose-specific, type 1 fimbrial adhesin of Escherichia coli, acquires amino acid replacements adaptive in extraintestinal niches (the genitourinary tract) but detrimental in the main habitat (the large intestine). This microevolutionary dynamics is reminiscent of an ecological “source-sink” model of continuous species spread from a stable primary habitat (source) into transient secondary niches (sink), with eventual extinction of the sink-evolved populations. Here, we have adapted two ecological analytical tools—diversity indexes D _S and α—to compare size and frequency distributions of fimH haplotypes between evolutionarily conserved FimH variants (“source” haplotypes) and FimH variants with adaptive mutations (putative “sink” haplotypes). Both indexes show two- to threefold increased diversity of the sink fimH haplotypes relative to the source haplotypes, a pattern that ran opposite to those seen with nonstructural fimbrial genes (fimC and fimI) and housekeeping loci (adk and fumC) but similar to that seen with another fimbrial adhesin of E. coli, papG-II, also implicated in extraintestinal infections. The increased diversity of the sink pool of adhesin genes is due to the increased richness of the haplotypes (the number of unique haplotypes), rather than their evenness (the extent of similarity in relative abundances). Taken together, this pattern supports a continuous emergence and extinction of the gene alleles adaptive to virulence sink habitats of E. coli, rather than a one-time change in the habitat conditions. Thus, ecological methods of species diversity analysis can be successfully adapted to characterize the emergence of microbial virulence in bacterial pathogens subject to source-sink dynamics. [Reviewing Editor: Dr. Margaret Riley]     

Eco-hydrological effects of landscape pattern change

Scientists and environmental managers alike are increasingly concerned about landscape pattern change and its effect on hydrological and ecological processes. In this paper, research progress is reviewed and key issues of eco-hydrological effects of landscape pattern change are discussed. There are different eco-hydrological effects with landscape pattern change, and most attention is paid to runoff, water quality, and soil loss. Landscape shape and spatial distribution can change precipitation-runoff processes and lead to the change in runoff yield. Water quality is closely connected with the composition and spatial pattern of source and sink landscapes. Soil erosion systems are usually modified by land use structure and landscape pattern, and soil loss will be either reduced or increased with land use change. In addition, the change of landscape pattern also has potential impacts on climate and soil quality. In future studies, more attention should be paid to comprehensive multi-scale and integrated research of landscape pattern and eco-hydrological processes.     

An improved neutral landscape model for recreating real landscapes and generating landscape series for spatial ecological simulations

Many studies have assessed the effect of landscape patterns on spatial ecological processes by simulating these processes in computer‐generated landscapes with varying composition and configuration. To generate such landscapes, various neutral landscape models have been developed. However, the limited set of landscape‐level pattern variables included in these models is often inadequate to generate landscapes that reflect real landscapes. In order to achieve more flexibility and variability in the generated landscapes patterns, a more complete set of class‐ and patch‐level pattern variables should be implemented in these models. These enhancements have been implemented in Landscape Generator (LG), which is a software that uses optimization algorithms to generate landscapes that match user‐defined target values. Developed for participatory spatial planning at small scale, we enhanced the usability of LG and demonstrated how it can be used for larger scale ecological studies. First, we used LG to recreate landscape patterns from a real landscape (i.e., a mountainous region in Switzerland). Second, we generated landscape series with incrementally changing pattern variables, which could be used in ecological simulation studies. We found that LG was able to recreate landscape patterns that approximate those of real landscapes. Furthermore, we successfully generated landscape series that would not have been possible with traditional neutral landscape models. LG is a promising novel approach for generating neutral landscapes and enables testing of new hypotheses regarding the influence of landscape patterns on ecological processes. LG is freely available online.     

Choosing appropriate temporal and spatial scales for ecological restoration

Classic ecological restoration seems tacitly to have taken the Clementsian “balance of nature” paradigm for granted: plant succession terminates in a climax community which remains at equilibrium until exogenously disturbed after which the process of succession is restarted until the climax is reached. Human disturbance is regarded as unnatural and to have commenced in the Western Hemisphere at the time of European incursion. Classic ecological restoration thus has a clear and unambiguous target and may be conceived as aiming to foreshorten the natural processes that would eventually lead to the climax of a given site, which may be determined by its state at “settlement”. According to the new “flux of nature” paradigm in ecology a given site has notelos and is constantly changing. Human disturbance is ubiquitous and long-standing, and at certain spatial and temporal scales is “incorporated”. Any moment in the past 10,000 years that may be selected as a benchmark for restoration efforts thus appears to be arbitrary. Two prominent conservationists have therefore suggested that the ecological conditions in North America at the Pleistocene—Holocene boundary, prior to the anthropogenic extinction of the Pleistocene megafauna, be the target for ecological restoration. That suggestion explicitly assumes evolutionary temporal scales and continental spatial scales as the appropriate frame of reference for ecological restoration. However, ecological restoration should be framed in ecological spatio-temporal scales, which may be defined temporally in reference to ecological processes such as disturbance regimes and spatially in reference to ecological units such as landscapes, ecosystems, and biological provinces. Ecological spatio-temporal scales are also useful in achieving a scientifically defensible distinction between native and exotic species, which plays so central a role in the practice of ecological restoration and the conservation of biodiversity. Because post-settlement human disturbances have exceeded the limits of such scales, settlement conditions can be justified scientifically as appropriate targets of restoration efforts without recourse to obsolete teleological concepts of equilibria and without ignoring the presence and ecological influence of indigenous peoples.     

景观格局-土壤侵蚀研究中景观指数的意义解释及局限性

景观格局分析是景观生态学研究的重要组成部分。景观指数是景观格局分析的有力工具。近年来,景观格局与土壤侵蚀关系的相关研究增多,常规景观格局指数得到应用。但针对土壤侵蚀过程的景观指数意义解释不足,景观指数在刻画景观格局-土壤侵蚀过程关系存在局限。选择了连接性、多样性、边界/斑块密度、形状4个方面的12个常用景观指数,对这些指数在景观格局-土壤侵蚀过程关系研究中的意义进行阐述,对指数应用的局限性及其原因进行了分析。景观数据属性、景观指数本身性质和土壤侵蚀过程的复杂性使得常规景观格局指数在景观格局-土壤侵蚀关系研究中存在不足。这3方面的影响使得常规景观格局指数与土壤侵蚀表征变量之间不存在确定的关系,从而难以通过景观指数来表征景观土壤侵蚀特征。缺乏土壤侵蚀过程基础是常规景观指数在土壤侵蚀研究应用中存在局限的主要原因。因此,构建基于土壤侵蚀过程的景观指数是景观格局-土壤侵蚀关系研究的需要和新的发展方向。     

中国景观生态学发展历程与未来研究重点

景观生态学从其诞生到现在,已经历了70余年。中国景观生态学的发展从其引入,到发展、壮大、逐渐成熟,也经历了30余年。在这个发展过程中,中国景观生态学在跟踪国际前沿研究基础上,结合中国实际情况开展了大量研究,在许多研究领域取得了重要进展。简述了国际景观生态学会成立与发展过程,通过系统综述中国景观生态学文献,重点分析了中国景观生态学的发展历程;根据中国景观生态学研究特点,将中国景观生态学发展划分为五个阶段:摸索与酝酿阶段(20世纪80年代以前)、吸收与消化阶段(1980—1988年)、实践与迅速发展阶段(1989—2000)、发展与思索阶段(2001—2010)、思考与创新阶段(2011—?)。在此基础上,重点从土地利用格局与生态过程及尺度效应、城市生态用地与景观安全格局构建、景观生态规划与自然保护区网络优化、森林景观动态模拟与生态系统管理、绿洲景观演变与生态水文过程、景观破碎化与遗传多样性保护、多水塘系统与湿地景观格局设计、稻-鸭/鱼农田景观与生态系统健康、梯田文化景观与多功能维持、源汇景观格局分析与水土流失危险评价等方面系统分析了中国景观生态学研究的特点。最后从学科发展与理论研究、重点研究地区和应用实践三个方面分析了中国景观生态学未来发展的重点方向。     

城市生态景观研究的基础理论框架与技术构架

构建人与自然和谐的生态景观是当今城市发展的重要目标之一,统一的内涵和完善的指标体系是城市生态景观规划和设计的迫切需求。通过概括城市生态景观的基本内涵和主要特征,认为其核心价值包括可持续性、生态经济效益及和谐性。据此,提出了8条指导原则,包括景观自然度、物种安全性和多样性、雨水利用效率、污染物排放和处理、绿色能源和材料利用、局地小气候调节、景观视觉享受以及精神内涵和文化品位,并根据文献资料和行业导则,整理并归纳了有关的定量评价指标和适用范围。最后总结了城市生态景观的技术构架,以及在资源保护和节约、功能与形式的有机结合、系统生态价值最大化等方面亟待解决的关键技术。为城市生态景观研究提供基础理论框架,也可以为城市生态景观的具体实践提供参考。     

An artificial neural network model of the landscape pattern in Shanghai metropolitan region, China

To characterize the urbanization pattern quantitatively, a study on the mechanisms of the landscape pattern formation could facilitate the understanding on urban landscape patterns and processes, the ecological and socioeconomic consequences of urbanization, as well as the establishment of more effective strategies for landscape management. In this study, we integrated a Geographic Information System (GIS)-based analysis on landscape pattern with an artificial neural network (ANN) to quantitatively characterize the urbanization pattern of the metropolitan area of Shanghai, China, and to establish an ANN model that could preferably simulate the responses of urban landscape pattern to the natural and socioeconomic factors such as residence area, road density, population density, urban development history and the Huangpu River as an element of economic change. Our results showed that the ANN model seems appropriate for studying the nonlinear relationship among the forcing factors of urbanization and the urban landscape patterns, which provided an effective and practical approach for further understanding the mechanisms of the landscape formation pattern and the reciprocal relationship between landscape spatial pattern and ecological process. __________ Translated from Acta Ecologica Sinica, 2005, 25(5): 958–964 [译自: 生态学报, 2005, 25(5): 958–964]