首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
This section measures your ability to understand academic passages in English. There are three passages in the section. Give you
This section measures your ability to understand academic passages in English. There are three passages in the section. Give you
admin
2014-09-29
37
问题
This section measures your ability to understand academic passages in English.
There are three passages in the section. Give yourself 20 minutes to read each passage and answer the questions about it. The entire section will take 60 minutes to complete.
You may look back at a passage when answering the questions. You can skip questions and go back to them later as long as there is time remaining.
Directions: Read the passage. Then answer the questions. Give yourself 20 minutes to complete this practice set.
HABITATS AND CHIPMUNK SPECIES
There are eight chipmunk species in the Sierra Nevada mountain range, and most of them look pretty much alike. But eight different species of chipmunks scurrying around a picnic area will not be found. Nowhere in the Sierra do all eight species occur together. Each species tends strongly to occupy a specific habitat type, within an elevational range, and the overlap among them is minimal.
The eight chipmunk species of the Sierra Nevada represent but a few of the 15 species found in western North America, yet the whole of eastern North America makes do with but one species: the Eastern chipmunk. Why are there so many very similar chipmunks in the West? The presence of tall mountains interspersed with vast areas of arid desert and grassland makes the West ecologically far different from the East. The West affords much more opportunity for chipmunk populations to become geographically isolated from one another, a condition of species formation. Also, there are more extremes in western habitats. In the Sierra Nevada, high elevations are close to low elevations, at least in terms of mileage, but ecologically they are very different.
Most ecologists believe that ancient populations of chipmunks diverged genetically when isolated from one another by mountains and unfavorable ecological habitat. These scattered populations first evolved into races—adapted to the local ecological conditions—and then into species, reproductively isolated from one another. This period of evolution was relatively recent, as evidenced by the similar appearance of all the western chipmunk species.
Ecologists have studied the four chipmunk species that occur on the eastern slope of the Sierra and have learned just how these species interact while remaining separate, each occupying its own elevational zone. The sagebrush chipmunk is found at the lowest elevation, among the sagebrush. The yellow pine chipmunk is common in low to mid-elevations and open conifer forests, including pinon and ponderosa and Jeffrey pine forests. The lodgepole chipmunk is found at higher elevations, among the lodgepoles, firs, and high-elevation pines. The alpine chipmunk is higher still, venturing among the talus slopes, alpine meadows, and high-elevation pines and junipers. Obviously, the ranges of each species overlap. Why don’t sagebrush chipmunks move into the pine zones? Why don’t alpine chipmunks move to lower elevations and share the conifer forests with lodgepole chipmunks?
The answer, in one word, is aggression. Chipmunk species actively defend their ecological zones from encroachment by neighboring species. The yellow pine chipmunk is more aggressive than the sagebrush chipmunk, possibly because it is a bit larger. It successfully bullies its smaller evolutionary cousin, excluding it from the pine forests. Experiments have shown that the sagebrush chipmunk is physiologically able to live anywhere in the Sierra Nevada, from high alpine zones to the desert. The little creature is apparently restricted to the desert not because it is specialized to live only there but because that is the only habitat where none of the other chipmunk species can live. The fact that sagebrush chipmunks tolerate very warm temperatures makes them, and only them, able to live where they do. The sagebrush chipmunk essentially occupies its habitat by default. In one study, ecologists established that yellow pine chipmunks actively exclude sagebrush chipmunks from pine forests; the ecologists simply trapped all the yellow pine chipmunks in a section of forest and moved them out. Sagebrush chipmunks immediately moved in, but yellow pine chipmunks did not enter sagebrush desert when sagebrush chipmunks were removed.
The most aggressive of the four eastern-slope species is the lodgepole chipmunk, a feisty rodent indeed. It actively prevents alpine chipmunks from moving downslope, and yellow pine chipmunks from moving upslope. There is logic behind the lodge-pole’s aggressive demeanor. It lives in the cool, shaded conifer forests, and of the four species, it is the least able to tolerate heat stress. It is, in other words, the species of the strictest habitat needs: it simply must be in those shaded forests. However, if it shared its habitat with alpine and yellow pine chipmunks, either or both of these species might outcompete it, taking most of the available food. Such a competition could effectively eliminate lodgepole chipmunks from the habitat. Lodgepoles survive only by virtue of their aggression.
Directions: Now answer the questions.
There are eight chipmunk species in the Sierra Nevada mountain range, and most of them look pretty much alike. But eight different species of chipmunks scurrying around a
picnic area
will not be found. Nowhere in the Sierra do all eight species occur together. Each species tends strongly to occupy a specific habitat type, within an elevational range, and the overlap among them is minimal.
Why does the author mention a "
picnic area
" in paragraph 1?
选项
A、To identify a site where a variety of different species of chipmunks can be seen
B、To support the point that each species of chipmunk inhabits a distinct location
C、To emphasize the idea that all species of chipmunks have a similar appearance
D、To provide an example of a location to which chipmunks are likely to scurry for food
答案
B
解析
转载请注明原文地址:https://kaotiyun.com/show/TUfO777K
0
托福(TOEFL)
相关试题推荐
Completethenotesbelow.WriteNOMORETHANTWOWORDSAND/ORANUMBERforeachanswer.DETAILSOFASSIGNMENTP
Completethetablebelow.WriteNOMORETHANTHREEWORDSforeachanswer.
Completethenotesbelow.WriteONEWORDAND/ORANUMBERforeachanswer.TheUndergroundHouseDesign
WhatrulesapplytotakingdifferentobjectstotheCentre?Matcheachobjectwiththecorrectrule,A-C.Writethecorrectlett
WhatdoesChloedecideaboutthefollowingsubjects?Writethecorrectletter,A,BorC,nexttoquestions26-30.AShewills
Completethenotesbelow.WriteNOMORETHANTWOWORDSforeachanswer.ROBERTSCOMPANYFoundingThemostimportantprincipalof
Completethenotesbelow.WriteONEWORDONLYforeachanswer.Episodicmemory-theabilitytorecalldetails,e.g.thetimeand
ChooseTWOletters,A-E.WhichTWOsubjectsdidMartinalikebestbeforegoingtouniversity?AArtBHistoryCFrenchDEnglish
Detailsofclimbingclub:excursiontoFranceinthe________
Whatistheprofessor’sopinionoftheconcertoscalledTheFourSeasons?
随机试题
金属材料受交变载荷而破坏的最大应力称为“疲劳极限”。
如何运用读书指导法?
进行尿液干化学法检测时,不受维生素C影响的指标是
A.普查B.抽样调查C.预调查D.捷径调查E.问卷调查在某小学进行牙病防治时用
施工分包单位对分包工程( )。
在代理税务行政复议时,关于税务行政复议的管辖原则,以下情况处理正确的有()。
下列四组机关部门中,可以联合行文的是()
文化反哺是指在急速的文化变迁时代所发生的年长一代向年轻一代进行广泛的文化吸收的过程。根据上诉定义,下列属于文化反哺的是:
下面两题基于以下题干:一般人认为,一个人80岁和他在30岁时相比,理解和记忆能力都显著减退。最近的一项调查显示,80岁的老人和30岁的年轻人在玩麻将时所表现出的理解和记忆能力没有明显差别。因此:认为一个人到了80岁理解和记忆能力会显著减退的看法是站
父图和其所有子图的总输入和总输出应完全一致,且它们的处理功能也应完全一致。这是数据流程图分解时应该遵循的一个基本原则,该原则称为______。
最新回复
(
0
)