Official 22 Set 5

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Pleistocene Rewilding

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What is the lecture mainly about?
  • A. A proposal to identify all the animals that became extinct during the Pleistocene epoch

  • B. A strategy for reintroducing native plants to an ecosystem

  • C. A process for identifying alternative habitats for large animals

  • D. A proposal to re-create features of ecosystems of the Pleistocene epoch

显示答案 正确答案: D

我的笔记 编辑笔记

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    NARRATOR:Listen to part of a lecture in a zoology class.

    FEMALE PROFESSOR:A mass extinction is when numerous species become extinct over a very short time period- short, geologically speaking, that is. Like, when the dinosaurs died out 65 million years ago.And the fossil record- it indicates that in all the time that animals have inhabited Earth, there've been five great mass extinctions, dinosaurs being the most recent.In each of the others, up to half of all land animals and up to 95 percent of marine species disappeared.

    Well, today, we're witnessing a sixth mass extinction, but unlike the others, the current loss of biodiversity can be traced to human activity.Since the Stone Age, humans have been eliminating species and altering ecosystems with astounding speed... countless species have disappeared due to overhunting, habitat destruction and habitat fragmentation, pollution, and other unnatural, human causes.

    [making main point finally]So, as a way of repairing some of that damage, a group of conservation biologists has proposed an ambitious- some might say a radical-plan involving large vertebrates, or megafauna.

    Megafauna include[tossing out examples] elephants, wild horses, big cats, camels-large animals.Uh, actually, the proposal focuses on a particular subset of megafauna- the kind that lived during the Pleistocene epoch.OK. The Pleistocene epoch, most commonly known as the Ice Age, stretched from 1.8 million to 11,500 years ago.In the Americas, most megafauna began disappearing by the end of the Pleistocene.

    So here is the biologists' idea: Take a select group of animals- megafauna from places like Africa and Asia, and introduce them into other ecosystems similar to their current homes, beginning in the western United States.They call their plan Pleistocene rewilding.

    Now, the advocates of Pleistocene rewilding cite two main goals.One is to help prevent the extinction of some endangered megafauna by providing new refuges, new habitats for them.The other's to restore some of the evolutionary and ecological potential that's been lost in North America.Wh-what do I mean by "restore evolutionary potential"?

    Well, as you know, the evolution of any species is largely influenced by its interactions with other species.So, during the Pleistocene epoch... let's take the now-extinct American cheetah, for instance.We believe it played a pivotal role in the evolution of the pronghorn antelope- the antelope's amazing speed, to be exact, because natural selection would favor those antelope that could outrun a cheetah.When the American cheetahs disappeared, their influence on the evolution of pronghorn, and presumably on other prey animals, stopped.

    So, it's conceivable that the pronghorn antelope would've continued to evolve, get faster maybe, if the cheetahs were still around.That's what's meant by "evolutionary potential."Importing African cheetahs to the western United States could, in theory, put the pronghorn back onto its, uh, natural evolutionary trajectory, according to these biologists.Another example is the interaction of megafauna with local flora- in particular, plants that rely on animals to disperse their seeds.Like, Pleistocene rewilding could spark the reemergence of large-seeded American plants, such as the maclura tree.

    Many types of maclura used to grow in North America, but today, just one variety remains, and it's found in only two states.In the distant past, large herbivores, like mastodons, dispersed maclura seeds, each the size of an orange, in their droppings.Well, there aren't any mastodons left, but there are elephants, which descended from mastodons.Introduce elephants into that ecosystem, and they might disperse those large maclura seeds, like their ancestors did.

    Get the idea?Restoring some of the former balance to the ecosystem?But, as I alluded to earlier, Pleistocene rewilding is extremely controversial.A big worry is that these transplanted megafauna might devastate plants and animals that are native to the western United States.In the years since the Pleistocene epoch, native species have adapted to the changing environment there... plants, smaller animals-they've been evolving without megafauna for millennia.

    Also, animal species that went extinct 11,000 years ago, uh, some are quite different genetically from their modern-day counterparts.Like elephants don't have thick coats like their mastodon ancestors did when they grazed the prairies of the American West during the Ice Age.Granted, the climate today is not as cold as it was in the Pleistocene, but winters on the prairie can still get pretty harsh today.

    And there are many more considerations-well, you see how complex this is.If you think about it, though, the core problem with this "sixth mass extinction" is human interference.Pleistocene rewilding's based on good intentions, but, you know... it probably would just be more of the same thing.

  • 旁白:听下面一段动物学课堂的讲解。

    教授:从地质学角度来讲大量消亡是指大规模的物种在短期内灭绝的现象,这里的短期,就是像六千五百万年前恐龙灭绝一样。而且化石记录显示,地球上生存过的物种已经经历过五次的大量消亡,恐龙灭绝是最近的一次。每次物种灭绝,多达半数的陆地动物和 95%的海洋生物彻底消失。

    那么今天我们正在目睹着第六次大量消亡,和前几次不一样,这次生物多样性的消失是由人类活动导致的。从石器时期开始,人类就在以惊人的速度消除物种,并改变着生态系统,不计其数的物种的消失都由于人类的过度捕猎、栖息处摧毁及破坏、污染及其他人类引起的非自然原因引起的。

    因此,作为对这些破坏的修复,一群保护主义生物学家提出了一个雄心勃勃的计划,有人可能会说这是个涉及大型脊椎动物或巨型动物的激进计划。

    巨型动物包括大象、野马、大型猫科动物、骆驼等。呃,其实,这项提议主要是针对一个居住于更新世的巨型动物支群。好的。更新世,也就是大家熟知的冰河时代,从一百八十万年前延伸至一万一千五百年前。在美洲,很多巨型动物在更新世后期开始消失。

    那么生物学家们的想法是这样的:从非洲及亚洲的地方选一批大型动物,然后把它们引进到与它们目前生活环境相似的生态系统中,从美国西部开始。他们称之为更新世野生动物重返计划。

    现在,更新世野生动物重返的提倡者们主要是有两大目标。一种是通过为他们提供新的避难所来帮助防止一些濒临灭绝的巨型动物的灭绝。另一个是重建北美已丧失的一些进化及生态的潜能。重建进化及生态的潜能是什么意思呢?

    你们都知道,物种的进化很大程度上受与其相互活动的物种的影响。所以在更新世时期,我们来拿已经绝种的美洲印度豹来举例。我们相信它在叉角羚的进化中起重要的作用,精确来讲,羚羊惊人的速度是一种自然选择的结果,因为只有能跑过印度豹的羚羊才能生存下来。当美洲印度豹绝种以后,它们对叉角羚及其他可能猎食的动物进化的影响就停止了。

    所以可以想象,如果印度豹还存在的话,叉角羚本可以继续进化,跑的更快。这就是进化潜能。按照这些生物学家的说法,从非洲向美国引进印度豹,在理论上就可以将叉角羚放回在其自然那的进化轨迹上来。另一个例子就是巨型动物和本地植物群的相互联系,尤其是那些仅依赖动物传播种子的植物。更新世野生动物重返可以促使美国一些种子颗粒大的植物重新出现,比如桑橙树。

    许多种类的桑橙树曾经在北美生长,而现在,只剩下了一种,而且仅在生长在两个州。在远古,大型的食草动物比如说乳齿象就传播桑橙树种子,橙子般大小的种子从它们的口中露出,便能得到传播。而现在已经没有乳齿象了,但是有大象,也就是乳齿象的后代。将大象引进到这个生态系统中可能就会帮助传播大颗粒种子了,正如它们的祖先一样。

    明白了吗?重建一些曾经的生态平衡?但是正如我之前暗指的一样,更新世野生动物重返非常的富有争议性。最让人忧心的就是这些转移过来的巨型动物可能会毁灭美国西部一些土生土长的动植物。自从更新世之后,本地的物种就一直在适应那里变化着的环境,植物、小动物在这个千年期内都是在没有巨型动物的环境下进化的。

    同样,这些一万一千年前就绝种的动物,和今天与其相似类的动物们基因有很大差异比如大象的祖先乳齿象有一层厚厚的皮,它们层在冰河时期的美国西部草原上吃草,而大象则没有。但是,今天的气候也不像更新世那时候那么冷,而草原上的冬天现在依旧是很严寒。

    而且还有众多需要考虑到的因素。如果你仔细的想一下,其实第六次大量消亡的核心问题是人类的干预。更新世野生动物重返计划意图是好的,但是你们知道,这很可能会使情况更加恶化。

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    题型分析:主旨题

    原文定位 Well, today we are witnessing a sixth mass extinction, but unlike the others, the current loss of bio-diversity can be traced to human activity. Since the Stone Age, humans have been eliminating species and altering ecosystems with astounding speed. Countless species have disappeared due to over-hunting, habitat destruction and habitat fragmentation, pollution and other unnatural human causes.

    So, as a way of repairing some of that damage, a group of conservation biologists has proposed an ambitious, or some might say, a radical plan, involving large vertebrates, or, megafauna. Megafauna include elephants, wild horses, big cats, camels, large animals. Eh, actually, the proposal focuses on a particular subset of megafauna, the kind that lived during the Pleistocene epoch.

    选项分析

    章前面一开始教授说到mass extinction human activity , 然后分别详细讲解了repairing 以及Pleistocene epoch. 最后提到prevent extinction 以及 restore lost.

    D选项即为文章核心名词repair 的同义替换,是对全文主旨最准确的概括

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