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托福备考第47天——TPO Extra 1 Reading ③

上一篇:托福备考第46天——TPO Extra 1 Reading ②




      The Black Hills forest, the prairie riparian forest, and other forests of the western United States can be separated by the distinctly different combinations of species they comprise. It is easy to distinguish between prairie riparian forest and Black Hills forest—one is a broad-leaved forest of ash and cottonwood trees, the other is a coniferous forest of ponderosa pine and white spruce trees. One has kingbirds; the other, juncos (birds with white outer tail feathers). The fact that ecological communities are, indeed, recognizable clusters of species led some early ecologists, particularly those living in the beginning of the twentieth century, to claim that communities are highly integrated, precisely balanced assemblages. This claim harkens back to even earlier arguments about the existence of a balance of nature, where every species is there for a specific purpose, like a vital part in a complex machine. Such a belief would suggest that to remove any species, whether it be plant, bird, or insect, would somehow disrupt the balance, and the habitat would begin to deteriorate. Likewise, to add a species may be equally disruptive.

      One of these pioneer ecologists was Frederick Clements, who studied ecology extensively throughout the Midwest and other areas in North America. He held that within any given region of climate, ecological communities tended to slowly converge toward a single endpoint, which he called the "climatic climax." This "climax" community was, in Clements's mind, the most well-balanced, integrated grouping of species that could occur within that particular region. Clements even thought that the process of ecological succession—the replacement of some species by others over time—was somewhat akin to the development of an organism, from embryo to adult. Clements thought that succession represented discrete stages in the development of the community (rather like infancy, childhood, and adolescence), terminating in the climatic "adult" stage, when the community became self-reproducing and succession ceased. Clements's view of the ecological community reflected the notion of a precise balance of nature.

      Clements was challenged by another pioneer ecologist, Henry Gleason, who took the opposite view. Gleason viewed the community as largely a group of species with similar tolerances to the stresses imposed by climate and other factors typical of the region. Gleason saw the element of chance as important in influencing where species occurred. His concept of the community suggests that nature is not highly integrated. Gleason thought succession could take numerous directions, depending upon local circumstances.

      Who was right? Many ecologists have made precise measurements, designed to test the assumptions of both the Clements and Gleason models. For instance, along mountain slopes, does one life zone, or habitat type, grade sharply or gradually into another? If the divisions are sharp, perhaps the reason is that the community is so well integrated, so holistic, so like Clements viewed it, that whole clusters of species must remain together. If the divisions are gradual, perhaps, as Gleason suggested, each species is responding individually to its environment, and clusters of species are not so integrated that they must always occur together.

      It now appears that Gleason was far closer to the truth than Clements. The ecological community is largely an accidental assemblage of species with similar responses to a particular climate. Green ash trees are found in association with plains cottonwood trees because both can survive well on floodplains and the competition between them is not so strong that only one can persevere. One ecological community often flows into another so gradually that it is next to impossible to say where one leaves off and the other begins. Communities are individualistic.

      This is not to say that precise harmonies are not present within communities. Most flowering plants could not exist were it not for their pollinators—and vice versa. Predators, disease organisms, and competitors all influence the abundance and distribution of everything from oak trees to field mice. But if we see a precise balance of nature, it is largely an artifact of our perception, due to the illusion that nature, especially a complex system like a forest, seems so unchanging from one day to the next.



Black hill 森林,草原河滨森林和美国西部其他森林的物种组合有着明显的不同。所以很容易区分black hill和草原河滨森林:一个是火山灰和杨木林组成的阔叶林,一个是由北美黄松和白云山组成的针叶林。一个有美洲食蜂鹟,一个有 灯芯草雀。生态群落确实是易于辨认的生物群体,这个事实让早期的生态学家,特别是那些生活在20世纪初期的生态学家做出声明,宣称群落是高度融合,精确平衡的集合体。这个声明可以追溯到早期关于自然平衡存在的观点--- 每个物种的存在都是有其特定的目的,就像是一部复杂机器的一个重要部分。在这个观点看来任何物种的移动,无论是植物,鸟类,或者昆虫,都可能会打破平衡,栖息地也可能开始恶化。同样地,增加一个物种也会导致破坏自然平衡。

生态学家著名先锋之一frederick clements,在中西部和南美其他地域做了大量的生态研究。他说在任何一个气候给定的区域,生态群落都会逐步覆盖成为一个单一的终结点,他称之为“气候性顶点”。 这种顶点群落,在Clement看来,是平衡性和融合性最好的物种,并且可能发生在任何独特的区域。Clements甚至认为生态演替的进程--- 随着时间推进一些物种被另外一些物种替代—多少有点类似有机物从胚胎到成熟状态的发展过程。Clements认为生态演替代表了群落发展的不连续的阶段进程 (就像婴儿期,儿童期,成人期),最终在成人时期达到顶点,在这个成人时期阶段群落开始进行独立繁殖,演替过程停止。Clements关于生态群落的观点反应了一个自然精确平衡的概念。

clements的观点受到了另外一个生态学家Henry的挑战。Henry认为群落大部分就是一个物种,对于来自于气候和地区其他典型条件的压力具有相似的容忍度。Henry认为在物种发生的地区机遇因素也很重要。他的群落概念表明自然不是高度融合, Henry认为生态演替依托于当地环境可能会有很多方向。



这并不是说精确的和谐在群落里是不存在的。大多数有花植物不能生存如果不给他们授粉,反之亦然。 捕食者,病原体,和竞争者都影响着每一个东西从橡树到田鼠的繁殖到分布。但是如果我们看到了自然精确的平衡,大部分都是我们意识里的假象,因为大自然,尤其是像森林那样复杂的系统,似乎每天都没有任何变化,所以我们会产生一种幻觉。


  • prairie 北美草原
  • riparian 河岸
  • comprise 包含
  • ash 灰
  • coniferous 针叶植物的
  • ponderosa 美国黄松
  • pine 松树;松木;(因死亡、离别) 难过,悲伤  
  • spruce 云杉
  • kingbirds 美洲食蜂鹟;王鸟
  • juncos 暗眼灯草鹀
  • clusters 簇
  • ecologists 生态学家
  • integrated 各部分密切协调的;综合的;完整统一的;(使)合并,成为一体;(使)加入,融入群体 【我理解为“集成”,因为集成电路叫Integrated circuit】
  • assemblages 集合; (人、物的)集聚
  • harken 倾听?(这个单词就没查到)
  • vital 至关重要的
  • disrupt 扰乱;使中断;打乱
  • deteriorate 变坏;恶化;退化
  • disruptive 引起混乱的;扰乱性的;破坏性的
  • ecologists 生态学家
  • Frederick Clements 弗雷德里克·克莱门茨
  • ecology 生态学
  • extensively 广大地;广泛地
  • converge 汇集;聚集;集中
  • climatic climax 气候高潮
  • succession 交替;更迭
  • akin to 类似于
  • embryo 胚胎
  • discrete 离散的;互不相连的
  • notion 概念
  • mountain slopes 山坡
  • divisions 分开; 分隔
  • holistic 整体的;全面的;功能整体性的
  • accidental 意外的
  • flood plains 洪泛平原  
  • persevere 坚持;孜孜以求
  • individualistic 个人主义的
  • pollinators 传粉者;(尤指)传粉昆虫
  • vice versa 反过来也一样;反之亦然
  • oak  橡树
  • mice 老鼠(复数)
  • artifact  人工制品;(尤指具有历史或文化价值的)手工制品,手工艺品
  • perception  n.知觉; 感知; 洞察力; 悟性; 看法; 见解


  • prairie riparian forest 草原河岸林
  • Black Hills forest 黑山森林



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This article was last edited at 2021-03-11 18:26:15

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