Directions: An introductory sentence for a brief summary of the passage is provided be

The phrase "by virtue of" in the passage is closest in meaning to

A．in spite of

B．because of

C．unconcerned about

D．with attention to

rodent indeed. It actively prevents alpine chipmunks from moving downslope, and yellow pine chipmunks from moving upslope. There is logic behind the lodge-poles 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.

According to paragraph 6, why is the lodgepole chipmunk so protective of its habitat from competing chipmunks?

A．It has specialized food requirements.

B．It cannot tolerate cold temperatures well.

C．It requires the shade provided by forest trees.

D．It prefers to be able to move between areas that are downslope and upslope.

at the end of paragraph 5?

A．The habitat of the yellow pine chipmunk is a desirable one to other species, but the habitat of the sagebrush chipmunk is not.

B．It was more difficult to remove sagebrush chipmunks from their habitat than it was to remove yellow pine chipmunks from theirs.

C．Yellow pine chipmunks and sagebrush chipmunks require the same environmental conditions in their habitats.

D．The temperature of the habitat is not an important factor to either the yellow pine chipmunk or the sagebrush chipmunk.

ks to their habitats EXCEPT:

A．Sagebrush chipmunks are able to survive in any habitat of the Sierra Nevada.

B．Sagebrush chipmunks occupy their habitat because of the absence of competition from other chipmunks.

C．Sagebrush chipmunks are better able to survive in hot temperatures than other species of chipmunks.

D．Sagebrush chipmunks spend the warm season at the higher elevations of the alpine zone.

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 word "encroachment" in the passage is closest in meaning to

A．complete destruction

B．gradual invasion

C．excessive development

D．substitution

to the other species of the eastern slope of the Sierra?

A．Below the sagebrush chipmunk

B．Above the alpine chipmunk

C．At the same elevation as the sagebrush chipmunk

D．Below the lodgepole chipmunk

ierra 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 dont sagebrush chipmunks move into the pine zones? Why dont alpine chipmunks move to lower elevations and share the conifer forests with lodgepole chipmunks?

Which of the sentences below best expresses the essential information in the highlighted sentence in paragraph 4? Incorrect choices change the meaning in important ways or leave out essential information.

A．Ecologists studied how the geographic characteristics of the eastern slope of the Sierra influenced the social development of chipmunks.

B．Ecologists learned exactly how chipmunk species separated from each other on the eastern slope of the Sierra relate to one another.

C．Ecologists discovered that chipmunks of the eastern slope of the Sierra invade and occupy higher elevational zones when threatened by another species.

D．Ecologists studied how individual chipmunks of the eastern slope of the Sierra avoid interacting with others of their species.

The phrase "one another" in the passage refers to

A．populations

B．races

C．ecological conditions

D．species

olated 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.

The word "diverged" in the passage is closest in meaning to

A．declined

B．competed

C．progressed

D．separated

tern North America because of

A．a large migration of chipmunks from eastern North America in an earlier period

B．the inability of chipmunks to adapt to the high mountainous regions of eastern North America

C．the ecological variety and extremes of the West that caused chipmunks to become geographically isolated

D．the absence of large human populations that discouraged species formation among chipmunks in the East