nity can also be viewed from the broader perspective<br /> Racerbaner n Free tsearchr Racerbaner s Racerbaner o Free  <embed src=""/>p Kategori c Free e  Racerbaner isearchesearchs Racerbaner t Trimmingsexystrippedmomanddaughter ,odsearchw Trimmingsexystrippedmomanddaughter b Racerbaner ,searchn Trimmingsexystrippedmomanddaughter rg Trimmingsexystrippedmomanddaughter   Trimmingsexystrippedmomanddaughter l Racerbaner wsearchasearchd<img src="http://img.alibaba.com/img/buyoffer/103622701/REFURBISHED_ANCHOR_HANDLING_VESSELS.jpg"/>tsearche<br />interactions among guilds of species.<br />Key Notes<br />The community<br />Q1 THE CPMMUNITY,STRUCTURE<br />AND STABILITY<br />群落结构<br />一个群落的物种多样性取决于群落含有的不同种的数<br />量即种丰富度（ the species richness）和种多度的均匀<br />性（ the evenness of species abundance）。多样性指数<br />（ diversity indices）可以通过这两个因子计算出来。表<br />达种丰富和种均匀度综合的另一种方式是通过种的相<br />对多度对种的顺序作图。多样性能够在局域群落<br />（ local community）、地区（ region）和最广阔的地理<br />尺度（ geographic scale）（如大陆）三个不同的空间尺<br />度上测算它。这样就产生了 a,β和 Υ多样性。<br />The species diversity of a community depends on the number<br />of different species it contains (the species richness) and the<br />evenness of species abundance across species,Diversity<br />indices can be calculated to take into account both of these<br />factors,Another way of representing species richness and<br />evenness together is to plot the relative abundance of species<br />against rank order of species abundance,Diversity can be<br />measured over the three different spatial scales of the local<br />community,the region and the broadest geographic scale (e.g,<br />the continent),This yields alpha (α)-,beta (β)-and gamma<br />(γ)-diversity,<br />Community<br />structure<br />群落边界 群落不会突然中断，而是逐渐的过渡到其他群落，因<br />为各个物种是逐渐受到它们的环境耐受力限制的。这<br />一点可以通过梯度分析来得到证明，梯率分析重点在<br />于物种分布重叠区域。分类和排序的统计方法允许群<br />落的边界在这个连续体上重叠。分类技术分出了生态<br />学上不同的物种或地段，获得了客观等级。排序并不<br />是企图勾画出边界，而是根据它们在分布上的相似性<br />而勾画出物种集团或地段。<br />Communities do not end abruptly but grade into one<br />another as individual species encounter the limits of their<br />environmental tolerance,This can be demonstrated<br />through gradient analysis,which focuses on the<br />overlapping distributions of individual species,The<br />statistical methods of classification and ordination allow<br />community boundaries to be superimposed on this<br />continuum,Classification techniques separate<br />ecologically different species or sites yielding objective<br />classes,Ordination does not attempt to draw boundaries<br />but groups species or sites according to how similar they<br />are in their distributions,<br />Community<br />boundaries<br />同资源种团 同资源种团是许多占据相似生态位的物种组合的集团；<br />如以阔叶树为食物的许多昆虫就形成一个同资源种团。<br />一些研究已经表明，在一个群落内的某些同资源种团<br />中的总物种的比例是不变的。这就表明也许有某一共<br />同的“规则”在统治着群落结构。<br />Guilds are groups of species that occupy similar niches;<br />for example,insects feeding on broad-leaved trees form<br />one guild,Some studies have found constancy in the<br />proportion of total species in certain guilds within a<br />community,This indicates that there may be certain<br />common ?rules‘ governing community structure.<br />Guilds<br />群落的复杂性、<br />多样性和<br />稳定性<br />稳定性有两个组成成分 ——恢复力（ resilience）和抵抗<br />力（ resistance）。这两个指标描述了群落在受到干扰<br />后的恢复能力和抵御变化的能力。复杂性被认为是决<br />定群落恢复力和抵抗力的重要因素。然而群落越复杂<br />并不意味着群落越稳定。复杂性增加已经显示会导致<br />不稳定。此外，群落的不同组分（如种丰富度和生物<br />量）也许对干扰有不同反应。具有较低生产力的群落<br />（如冻原）其恢复力是最低的。相反，较弱的竞争可<br />以使许多的物种共存，从而减少群落的不稳定性。<br />There are tow components to stability – resilience and<br />resistance,which describe the community‘s ability to<br />recover from disturbance and to resist change,Complexity<br />is thought to be important in determining resilience and<br />resistance,However,more complex communities are not<br />necessarily the most stable; increased complexity has been<br />shown to lead to instability,In addition,different<br />components of the communities (e.g,species richness and<br />biomass) may respond differently to disturbance,<br />Communities with a low productivity (e.g,tundra) to be<br />the least resilient,In contrast,weak competition permits<br />coexistence among species and reduces community<br />instability.<br />Community<br />complexity,diversity<br />and stability<br />相关主题 资源分配（见 I3） 食物链（见 P3）<br />营养复杂性与<br />稳定性<br />食物链的长度也许能够影响群落的恢复力。具有不同<br />营养连接水平的许多群落模型，显示复杂性导致恢复<br />力和稳定性下降。然而，这样的研究应该被谨慎地解<br />释，因为真正的群落所具有的特性在零群落模型中并<br />没有被发现。稳定性也依赖于环境状况 ——一个脆弱<br />的（复杂的或多样的）群落也许能够在一个稳定和可<br />预知的环境中持续下去，而在一个多变的和不可预知<br />的环境中，仅仅简单的和生长旺盛的群落才能够生存<br />下去。<br />Related topics Resource partitioning (I3) Food chains (P3)<br />Trophic complexity<br />and stability<br />Food chain length may influence the resilience of the<br />community,Models of communities with different levels<br />of trophic connectance show that complexity reduces<br />resilience and stability,However,such studies should be<br />interpreted with caution,as real communities msy possess<br />important attributes mot found in the communities of null<br />models,Stability also depends on environmental<br />conditions – a fragile (complex or diverse) community<br />may persist in a stable and predictable environment,while<br />in a variable and unpredictable environment only simple<br />and robust communities will survive.<br />Q2 岛屿群落与移殖<br />要 点<br />物种 -面积关系 岛屿上（或一个地区中）物种数目会随着岛屿面积的<br />增加而增加，最初增加十分迅速，当物种接近该生境<br />所能承受的最大数量时，增加将逐渐停止。物种数目<br />的对数与面积对数的坐标图显示的是一个线性关系。<br />对于海洋岛屿和生境岛屿来说，这些双对数坐标图直<br />线的斜率，大多在 0.24~0.34之间。对于连续生境内的<br />亚区域，斜率接近 0.1。随着面积增加，物种多样性增<br />加的效果在岛屿上要比连续生境内明显。<br />The number of species on an island (or in any area) will<br />increase with the size of the island,The increase is initially<br />rapid,tailing off at the maximum number of species for a given<br />habitat,A plot of log species number against log area gives a<br />linear relationship,For oceanic islands or islands of habitat,the<br />slopes of these log-log plots mostly fall within the range 0.24-<br />0.34,For subareas within continuous habitat,the slope is<br />around 0.1,The effect of increasing species diversity with<br />increasing area is more pronounced on islands than within<br />continuous habitat.<br />Key Notes<br />The species-area<br />relationship<br />Q2 ISLAND COMMUNITIES<br />AND COLOMOZATION<br />岛屿生物<br />地理学<br />麦克阿瑟和威尔逊的岛屿生物地理学理论指出，岛屿<br />上物种的数目是由新移殖来的物种和以前存在物种的<br />灭绝之间的动态平衡决定的。当移殖种的数目增加时，<br />到达岛屿的移殖来的物种的数目会随着时间的推移而<br />减少。相反，当物种之间的竞争变得强烈时，灭绝的<br />速率就会增加。当灭绝和移殖的速率达到相等时，物<br />种的数目就处于平衡稳定状态。模型研究也证明了物<br />种的数目会随着岛屿面积的增加而增加，和随着距移<br />殖者源距离的缩短而增加。对模型研究有利的证据，<br />是由对除去动物的岛屿上物种的再移殖的观察，和对<br />最近隔离的岛屿物种的丧失结果所提供的。当与邻近<br />大陆对照的时候，灭绝和移殖过程说明了岛屿植物区<br />系和动物区系的衰亡。<br />MacArthur and Wilson‘s theory of island biogeography states<br />that the number of species found on an island is determined<br />by a dynamic equilibrium between the immigration of new<br />colonizing species and the extinction of previously established<br />ones,As the number of colonizing species increases,the<br />number of immigrants arriving on the island decreases over<br />time,In contrast,as competition among species becomes more<br />intense,the extinction rate increases,The point at which<br />extinction and colonization rates are equal gives the number<br />of species at equilibrium,the model also accounts for the<br />increase in species number with increasing island size and<br />decreasing distance from a source of colonists,Extinction and<br />colonization account for the depauperate flora and fauna of<br />islands when compared to the adjacent mainland.<br />Island<br />biogeography<br />岛屿和异质<br />种群<br />异质种群理论已经替代了岛屿生物地理学来解释片断<br />化生境的“岛屿”种群行为。异质种群含有许多种群，<br />这些种群之间通过迁入和迁出而交换个体。与岛屿不<br />同，生境斑块（ patch）是在景观镶嵌板块（ landscape<br />mosaic）之中的，景观板块能够影响斑块的性质和它所<br />含的物种种类。<br />相关主题 种内竞争（见 I2） 保育对策（见 V2）<br />稀有物种、生境损失和灭绝（见 V1）<br />Related topics Intraspecific competition (I2) Conservation strategies (V2)<br />Rare species,habitat loss and<br />extinction (V1)<br />Islands and<br />metapopulations<br />Metapopulation theory has superseded island<br />biogeography in explaining the behavior of populations in<br />?islands‘ of fragmented habitat,A metapopulation consists<br />of a number of populations that exchange individuals<br />through immigration and emigration,Unlike islands,<br />habitat patches are embedded in a landscape mosaic that<br />can influence the quality of the patch and the species it<br />will contain.<br />Q3 群落格局、竞争和捕食<br />要 点<br />群落集合 集合规则（ assembly rule）的概念企图解释自然群落<br />是如何不同于来自物种库中的物种而随机装配出来的<br />群落。群落集合也许能被生境类型、物种移殖和定居，<br />或者种内的相互关系，像捕食、寄生和竞争所影响。<br />集合规则研究群落组成中的格局，将那些由“零<br />(null)‖群落模型所产生的格局与真实的群落格局相比<br />较。<br />The concept of assembly rules attempts to explain how<br />natural communities vary from random assemblages derived<br />from the range of available species (the species pool),<br />Community assembly may be influenced by habitat type,<br />species colonization and establishment,and /or by<br />interspecific relationships such as predation,parasitism and<br />competition,Assembly rule studies investigate patterns in<br />community make- up,comparing real community patterns<br />with those generated by ?null‘ community models.<br />Key Notes<br />Community<br />assembly<br />Q3 COMMUNITY PATTERNS,<br />COMPETITION AND PREDATION<br />竞 争 竞争可能是形成群落结构的一个重要力量，但是在调<br />查的时候，它又不一定是重要的。过去竞争的痕迹在<br />群落中可以留下很深的烙印（像生态位的分化）。竞<br />争的一些研究已经表明，生态学上相似物种组成的同<br />资源种团当中，仅仅只有一个成员在群落中能够生存，<br />这就意味着其他相似物种被竞争排斥了。岛屿上超飘<br />流的鸟类物种的分布也支持了该理论，即竞争导致了<br />群落的结构化。<br />Competition can be an important force shaping community<br />structure but is not necessarily significant at the time of<br />investigation,The ghost of competition past can leave a<br />strong imprint on a community (e.g,as niche differentiation),<br />Some studies of competition have shown that only one<br />member of a guild of ecologically similar species tends to be<br />present in the community,suggestive of competitive<br />exclusion of other similar species,The distribution of<br />supertramp bird species on islands also supports the theory<br />that communities are structured by competition.<br />Competition<br />食肉动物 选择捕食和转换猎物能够使稀有物种免遭捕杀。这种<br />行为能够导致许多相对稀少的物种在同一个群落中共<br />存。<br />食草动物 食草动物对植物群落有两个作用：（ i）它们选择摄食<br />影响群落的物种多度。（ ii）啃食抑制了竞争物种的生<br />长，因此加速和维持了低竞争物种的多样性。当啃食<br />强度很强时，物种多样性降低，物种会局部灭绝。<br />Grazing animals have two effects on plant communities,(i)<br />their selective feeding affects species abundance in the<br />community,and (ii) grazing suppresses the growth of<br />competitive species thus enhancing and maintaining the<br />diversity of less competitive species,When grazing intensity<br />is very high,diversity can be reduced as species are forced<br />to local extinction.<br />Grazers<br />Selective predation and prey switching can leave rarer<br />species unpredated,This behavior can lead to the<br />coexistence of a large number of relatively rare species in<br />the same community.<br />Carnivores<br />相关主题 种内竞争（见 I2） 演替（见 R1）<br />资源分配（见 I3） 群落对干扰的反映（见 R2）<br />关键物种 关键（ keystone）物种在群落中有一个重要的和不成比<br />例的作用。关键种可能是顶端的捕食者，像北方的海<br />獭；然而这个词可以运用在任何一个物种上，只要这<br />个物种被移去时会对群落结构造成重大影响。<br />Related topics Intraspecific competition (I2) Community responses to<br />Resource partitioning (I3) disturbance (R2)<br />Succession (R1)<br />Keystone species A keystone species has a significant and disproprtionate effect on the community,Keystone species can be top<br />predators such as the northern sea otter; however,the term<br />can be usefully applied to any species whose removal<br />would have a significant effect on community structure.<br />R1 演 替<br />要 点<br />演替 ——经典<br />模型<br />生态演替是指在一个自然群落中，物种的组成连续地、<br />单方向地、有顺序地变化。这一顺序被称为是一个演<br />替序列，最后达到的阶段称为顶级。早期的演替阶段，<br />具有先锋物种、低生物量和低营养水平的特征。随着<br />演替的进行，群落的复杂性增加，通常在演替的中期<br />阶段，复杂性达到最大。一个中期的演替群落具有高<br />生物量、高有机营养水平和高的物种多样性。<br />Ecological succession is defined as a continuous,<br />unidirectional,sequential change in the species<br />composition of a natural community,This sequence of<br />community is termed a sere,and culminates in the climax<br />community,Early successional stages are characterized by<br />pioneer species,low biomass and often low nutrient levels,<br />Community complexity increases as succession progresses,<br />often peaking in the mid-successional stage,A mid-<br />successional community is characterized by high biomass,<br />high levels of organic nutrients and high species diversity.<br />Key Notes<br />Succession –the<br />classical model<br />R1 SUCCESSION<br />自发演替 自发演替的动力来自于生物与它们环境之间的相互作<br />用。原生演替（ primary succession）发生在新近形成的<br />基质上，如冰川沉积物。先锋物种的营养物的增减和<br />腐殖质的积累为新物种移殖做好了准备。次生演替是<br />由于干扰引起的，如洪水、火灾和人类活动。在这两<br />种自然发生的演替中先锋物种的移殖很快，在较强竞<br />争力的物种入侵之前充分利用空间。耐阴物种（ shade-<br />tolerant species）成为阴影处的主宰者，它们是一些较<br />慢的移殖者。<br />Autogenic succession is self-driven,resulting from the<br />interaction between organisms and their environment,<br />Primary succession occurs on a newly formed substrate<br />such as glacial till,Nutrient enhancement and litter<br />accumulation by pioneer species allow new species to<br />colonize,Secondary succession follows disturbance,for<br />example by flooding,fire or human activity,In both types<br />of autogenic succession pioneer species colonize quickly<br />making opportunistic use of resources before the invasion<br />of more competitive species,Shading leads to dominance<br />by shade-tolerant species which tend to be slow colonizers.<br />Autogenic<br />succession<br />退行性演替 退行性演替是涉及到移殖和死亡有机体后来腐烂分解<br />的自发演替的一种类型。当有机物质降解耗尽了一些<br />资源和制造了其他可以利用的资源的时候，不同的物<br />种就交替地出现和消失。这个过程导致了腐殖质的生<br />产，并且对土壤形成过程起着重要作用。<br />异发演替 异发演替是由外界环境因素引起的，像长期的气候变<br />化（如冰河时期）和环境在短时间内的变化（如沉积<br />物的增加）。群落结构随时间的变化从沉积物芯样的<br />花粉分析来看是十分明显的。演替依赖于物种对环境<br />条件（如盐分）的忍耐性。<br />Degradative succession is a type of augogenic succession<br />involving colonization and subsequent decomposition of dead<br />organic matter,Different species invade and disappear in turn,<br />as the degradation of the organic matter uses up some resources<br />and makes others available,This process leads to the<br />production of humus and is important in soil formation.<br />Degradative<br />succession<br />Allogenic succession results from external environmental<br />factors,such as long term climatic change (e.g,ice ages) or<br />environmental change over a short time (e.g,sediment<br />accretion),Changes in community structure over time are<br />apparent from pollen analysis of sediment cores,Successional<br />progress depends on species tolerance to environmental<br />conditions such as salinity.<br />Allogenic<br />succession<br />演替过程 演替受三个过程的强烈影响：<br />（ i）促进：正在发展的群落所产生的非生物环境变化，<br />允许其他物种的入侵。<br />（ ii）抑制：一个阶段的物种抵制后来演替的物种的入<br />侵，以至于入侵仅仅在干扰或死亡后才有可能。<br />（ iii）耐受：后期演替的物种的入侵，因为它仍能够忍<br />受较低的资源水平和排斥早期演替的物种。能忍受低<br />资源水平的强竞争的物种，将取代好的机会迁移者而<br />统治顶极群。<br />Succession is strongly influenced by three processes.<br />(i) Facilitation,changes in the abiotic environment that are<br />imposed by the developing community and allow other<br />species to invade.<br />(ii) Inhibition,species of one stage resist invasion