文章来源:未知 文章作者:enread 发布时间:2023-08-21 08:49 字体: [ ]  进入论坛
browsing1 medium sized antelopesBrowsing antelope2 turned ancient African forests into grassy4 savanna5 ecosystems6
Millions of years ago, Africa's savannas7 were covered with thick, ancient forests, which disappeared and turned into the grassy ecosystems that they are today. Almost a fifth of the world's land surface is covered by savannas. Yet, for years it has been a mystery how these grassy ecosystems came to replace the ancient forests.
One answer, it was thought, might be climate change, yet most savannas occur in climates that also support forests. The other possibility was fire. Savanna trees and shrubs8 are often adapted to frequent fires, while forest trees are not.
But a study that includes a group of South African scientists has found that the arrival of browsing medium sized antelopes3 was probably what turned Africa's ancient forests into the open savannas.
By comparing the timing9 of the evolution of thorns on about 2000 woody tree species in southern Africa and the time that antelopes arrived in Africa, a group of scientists, including Dr Gareth Hempson from the School of Animal Plants and Environmental Studies at the University of Witwatersrand, found that trees like African acacias evolved thorns as a defence mechanism10 at exactly the same time that antelope arrived in Africa.
通过比较南部非洲约2000种木本树种刺的进化时间和羚羊到达非洲的时间,包括威特沃特斯兰德大学动植物与环境研究学院的Gareth Hempson博士在内的一组科学家,发现像非洲acacias这样的树在羚羊到达非洲的同时进化出刺作为防御机制。
"It all makes perfect sense," says Hempson. "Spines11 (thorns) really appear to be most effective against medium- and large-sized browsers12 like impala and kudu, and spiny13 trees are most common in the places where these animals are most abundant," says Hempson.
"We were shocked," said Professor van der Bank "to discover that spiny plants only appeared about 15 million years ago, 40 million years after mammals replaced dinosaurs14". For most of this time, Africa was an island continent dominated by now-extinct ancestors of browsing elephants and hyrax. "Apparently15, spines just didn't work as a plant defense16 against these ancient mammal groups" commented Prof van der Bank.
But in a remarkable17 example of apparent coevolution, the diversification18 of spiny plants (thorn trees) coincides with the appearance of antelope.
Antelope were latecomers to Africa appearing only after the continent collided with Eurasia. They browsed19 in novel ways and were highly efficient herbivores. This injection of new types of browsers, argue the authors, demolished20 young forest trees, opening up forests to the grass invaders21.
The parallel radiation of spiny plants and the antelope that feed on them initiated22 the rise of savannas in the drier more fertile regions of Africa. Fire only began to roll back the forests to create wetter savannas several million years later.
One implication of the study is that the loss of Africa's native browsing antelope may threaten the future of drier savannas, and lead to their replacement23 by dense24, woody scrub of little ecological25 or economic value.


1 browsing 509387f2f01ecf46843ec18c927f7822     
v.吃草( browse的现在分词 );随意翻阅;(在商店里)随便看看;(在计算机上)浏览信息
  • He sits browsing over[through] a book. 他坐着翻阅书籍。 来自《简明英汉词典》
  • Cattle is browsing in the field. 牛正在田里吃草。 来自《简明英汉词典》
2 antelope fwKzN     
  • Choosing the antelope shows that China wants a Green Olympics.选择藏羚羊表示中国需要绿色奥运。
  • The tiger was dragging the antelope across the field.老虎拖着羚羊穿过原野。
3 antelopes ca529013a9640792629d32a14a98d705     
羚羊( antelope的名词复数 ); 羚羊皮革
  • One jump, and you're out, and we'll run for it like antelopes.' 你只要一跳就出来了,我们可以像羚羊那样飞快地逃掉。”
  • Most antelopes can withhold their young for weeks, even months. 绝大部分羚羊能把分娩期推迟几个星期,甚至几个月。
4 grassy DfBxH     
  • They sat and had their lunch on a grassy hillside.他们坐在长满草的山坡上吃午饭。
  • Cattle move freely across the grassy plain.牛群自由自在地走过草原。
5 savanna bYbxZ     
  • The savanna is also the home of meat-eaters--the lion,leopard,and hyena who feed on the grasseaters.大草原也是食肉动物的家乡--狮子、豹、鬣狗--它们都是以草食动物维持生命的。
  • They sped upon velvet wheels across an exhilarant savanna.他们的马车轻捷地穿过一片令人赏心悦目的大草原。
6 ecosystems 94cb0e40a815bea1157ac8aab9a5380d     
n.生态系统( ecosystem的名词复数 )
  • There are highly sensitive and delicately balanced ecosystems in the forest. 森林里有高度敏感、灵敏平衡的各种生态系统。 来自《简明英汉词典》
  • Madagascar's ecosystems range from rainforest to semi-desert. 马达加斯加生态系统类型多样,从雨林到半荒漠等不一而足。 来自辞典例句
7 savannas 8e6e2e0a16919eb825681014ced032b7     
n.(美国东南部的)无树平原( savanna的名词复数 );(亚)热带的稀树大草原
  • Therefore the jungles and the savannas know of no juvenile delinquency! 因此,丛林和荒原里没有“少年犯罪。” 来自辞典例句
  • My soul flits away into the virgin forests and to the savannas. 我的灵魂飞向森林中的处女地和广漠的平原。 来自互联网
8 shrubs b480276f8eea44e011d42320b17c3619     
灌木( shrub的名词复数 )
  • The gardener spent a complete morning in trimming those two shrubs. 园丁花了整个上午的时间修剪那两处灌木林。
  • These shrubs will need more light to produce flowering shoots. 这些灌木需要更多的光照才能抽出开花的新枝。
9 timing rgUzGC     
  • The timing of the meeting is not convenient.会议的时间安排不合适。
  • The timing of our statement is very opportune.我们发表声明选择的时机很恰当。
10 mechanism zCWxr     
  • The bones and muscles are parts of the mechanism of the body.骨骼和肌肉是人体的组成部件。
  • The mechanism of the machine is very complicated.这台机器的结构是非常复杂的。
11 spines 2e4ba52a0d6dac6ce45c445e5386653c     
n.脊柱( spine的名词复数 );脊椎;(动植物的)刺;书脊
  • Porcupines use their spines to protect themselves. 豪猪用身上的刺毛来自卫。
  • The cactus has spines. 仙人掌有刺。 来自《现代英汉综合大词典》
12 browsers b559db93c279b7e4886705cb45f7ca9c     
  • Three-layer architecture is a model made up of browser, web server and background database server. 这种体系结构是由Browser、Web Server、Database Server组成的浏览器/Web服务器/后台数据库服务器三层模型。 来自互联网
  • Another excellent approach is to abandon the browser entirely and, instead, create a non-browser-based, Internet-enabled application. 另一个非常好的方法是干脆放弃浏览器,取而代之,创建一个不基于浏览器,但却是基于互联网的应用。 来自About Face 3交互设计精髓
13 spiny 3F9zU     
  • This is the Asiatic ornamental shrub with spiny branches and pink blossoms.这就是亚洲的一种观赏灌木,具有多刺的枝和粉红色的花。
  • Stay away from a spiny cactus.远离多刺仙人掌。
14 dinosaurs 87f9c39b9e3f358174d58a584c2727b4     
n.恐龙( dinosaur的名词复数 );守旧落伍的人,过时落后的东西
  • The brontosaurus was one of the largest of all dinosaurs. 雷龙是所有恐龙中最大的一种。 来自《简明英汉词典》
  • Dinosaurs have been extinct for millions of years. 恐龙绝种已有几百万年了。 来自《简明英汉词典》
15 apparently tMmyQ     
  • An apparently blind alley leads suddenly into an open space.山穷水尽,豁然开朗。
  • He was apparently much surprised at the news.他对那个消息显然感到十分惊异。
16 defense AxbxB     
  • The accused has the right to defense.被告人有权获得辩护。
  • The war has impacted the area with military and defense workers.战争使那个地区挤满了军队和防御工程人员。
17 remarkable 8Vbx6     
  • She has made remarkable headway in her writing skills.她在写作技巧方面有了长足进步。
  • These cars are remarkable for the quietness of their engines.这些汽车因发动机没有噪音而不同凡响。
18 diversification 8scxf     
  • The seminar was to discuss diversification of agriculture. 该研讨会讨论的是农业多种经营。 来自辞典例句
  • Firm diversification is increasingly achieved by the means of takeover and merger. 通过接管和兼并,厂商经营范围日益多样化。 来自辞典例句
19 browsed 86f80e78b89bd7dd8de908c9e6adfe44     
v.吃草( browse的过去式和过去分词 );随意翻阅;(在商店里)随便看看;(在计算机上)浏览信息
  • I browsed through some magazines while I waited. 我边等边浏览几本杂志。 来自辞典例句
  • I browsed through the book, looking at page after page. 我翻开了一下全书,一页又一页。 来自互联网
20 demolished 3baad413d6d10093a39e09955dfbdfcb     
v.摧毁( demolish的过去式和过去分词 );推翻;拆毁(尤指大建筑物);吃光
  • The factory is due to be demolished next year. 这个工厂定于明年拆除。
  • They have been fighting a rearguard action for two years to stop their house being demolished. 两年来,为了不让拆除他们的房子,他们一直在进行最后的努力。
21 invaders 5f4b502b53eb551c767b8cce3965af9f     
入侵者,侵略者,侵入物( invader的名词复数 )
  • They prepared to repel the invaders. 他们准备赶走侵略军。
  • The family has traced its ancestry to the Norman invaders. 这个家族将自己的世系追溯到诺曼征服者。
22 initiated 9cd5622f36ab9090359c3cf3ca4ddda3     
n. 创始人 adj. 新加入的 vt. 开始,创始,启蒙,介绍加入
  • He has not yet been thoroughly initiated into the mysteries of computers. 他对计算机的奥秘尚未入门。
  • The artist initiated the girl into the art world in France. 这个艺术家介绍这个女孩加入巴黎艺术界。
23 replacement UVxxM     
  • We are hard put to find a replacement for our assistant.我们很难找到一个人来代替我们的助手。
  • They put all the students through the replacement examination.他们让所有的学生参加分班考试。
24 dense aONzX     
  • The general ambushed his troops in the dense woods. 将军把部队埋伏在浓密的树林里。
  • The path was completely covered by the dense foliage. 小路被树叶厚厚地盖了一层。
25 ecological IrRxX     
  • The region has been declared an ecological disaster zone.这个地区已经宣布为生态灾难区。
  • Each animal has its ecological niche.每种动物都有自己的生态位.
TAG标签: 非洲 森林 草原