The “balance of nature is not an empty phrase. Nature provides a population to o

The “balanceof nature”is not an empty phrase. Natureprovides a population to occupy a suitable environment and cuts down surpluspopulation to fit the available food supply. One means of reducing surpluspopulation is predators; others are parasitic diseases. Also, populationdensity produces nervous disorders and even drives animals to mass migrations(移民群),like the lemmings of Norway who plunge（冲入）into the sea.

That predatory population increase tocontrol other animals has long been known. Many years ago, the Hudson’s BayCompany records revealed that the fox population went up and down about a yearafter rabbit population had gone up and down.

Sometimes a situation occurs in which thepredatory population is reduced to a level below which nature can readilyreplace. On Valcour Island in Lake Champlain, a costly campaign resulted in theelimination（消除）of predatory animals only tohave birds and small animals increase for four years afterward. Then, lackingpredator control, nature resorted to disease to cut down these populations.

Jamaica had an example of nature’spersistence in providing animals for existing habits. Sugar planters, about 75years ago, imported mongooses（狐猴）to control rats. The mongooseskilled off the rats, kids, puppies, and wildlife. Eventually, food becamescarce and the mongoose’s population declines.

1. The fact that the number of predatorshas much to do with that of other animals   .

A. is not recent knowledge    B.hasjust been learned

C.hasn’t been proved yet  D.isnot important now

2. When predator control fails, naturebrings animal population into balance by       .

A. eliminating the number of predators

B.seeking the help of disease to reduceother animals

C.increasing the number of other animals

D.replacing the number of predatorsimmediately

3. When the mongooses killed off the ratsthey   .

A. became problems themselves B.atethe sugar crop

C.attacked humans   D.hadnothing to eat

4. It is implied in this passage that   .

A. sugar planter imported mongooses tocontrol rats

B.man should never kill animals

C.man has complete control over nature

D.to upset the balance of nature can betroublesome

试题答案

答案：A;B;A;D