entry to it is costless, but exit from it is costly

entry to it is costly, but exit from it is costless

entry to it and exit from it are both costly

entry to it and exit from it are both costless

THE INTRODUCTION OF PREDATORS.

PREVENTING THE KIWI DECLIN E.

REASONS FOR CONCER N. D.EXPLANATION FOR LARGER BIRD POPULATIONS. E.LAND OF THE KIW I. KIWIS ARE FLIGHTLESS BIRDS ENDEMIC TO NEW ZEALAND, AND BY FAR THE SMALLEST LIVING RAT-ITES AND LAY THE LARGEST EGG IN RELATION TO THEIR BODY SIZE OF ANY SPECIES OF BIRD IN THE WORL D. 【A1】______ THE KIWI IS SYNONYMOUS WITH NEW ZEALAND, SO MUCH SO THAT AUSTRALIANS ENDEARINGLY REFER TO NEW ZEALANDERS AS 'KIWI' —PEOPLE FROM THE LAND OF THE KIW I.THIS UNIQUE BIRD, RECOGNIZABLE BY ITS SHORT SQUAT BODY AND ELONGATED BEAK, IS UNDER THREAT.ITS SMALL, CLAWLIKE WINGS RENDER THE KIWI FLIGHTLESS; IT MUST OF NECESSITY LIVE ON THE GROUN D.THE KIWI IS THUS EASY PREY TO MARAUDING ENEMIES SUCH AS HUMANS AND MAMMALS. 【A2】______ WHEN THE GREAT LAND MASS OF THE SOUTH SPLIT 75 MILLION YEARS AGO, THE KIWI AND MANY OTHER GROUND-LIVING BIRD SPECIES BECAME SEPARATED FROM PREDATORY MAMMALS WITHIN WHAT WAS LATER TO BECOME KNOW AS NEW ZEALAN D.THE BIRDS WERE ABLE TO MULTIPLY AND FLOURISH BECAUSE THERE WERE VERY FEW MAMMALS LANDLOCKED WITHIN THE ISLANDS.KIWIS HAVE EVOLVED CERTAIN MAMMALIAN CHARACTERISTICS OVER TIME, LIVING ON THE GROUND AND FREE AS THEY WERE FROM ATTACK BY MAMMALS. 【A3】______ HOWEVER, WHEN THE POLYNESIANS ARRIVED ABOUT 1,000 YEARS AGO BRINGING WITH THEM DOGS AND RATS, THE KIWI POPULATION AND OTHER VULNERABLE BIRD SPECIES SOON SUFFERED A SEVERE REDUCTION IN NUMBERS.THE COMING OF THE EUROPEANS IN THE EIGHTEENTH CENTURY BROUGHT EVEN MORE DETERMINED PREDATORS, INCLUDING THE CAT AND, ESPECIALLY, THE STOAT —A KIND OF WEASEL INTRODUCED TO CONTROL RABBITS.THE STOAT IS A VERY VICIOUS AND EFFICIENT KILLER OF KIWIS. 【A4】______ THERE ARE SIX TYPES OF KIWIS, AND ALL SIX ARE THREATENE D.TWO ARE 'CRITICALLY ENDANGERED' BECAUSE THEY HAVE POPULATIONS OF LESS THAN 250 MATURE BIRDS.TWO ARE 'ENDANGERED' MEANING THAT IT IS ESTIMATED THAT WITHIN THREE GENERATIONS THEIR NUMBERS WILL HAVE DECLINED BY 50%.THE OTHER TWO ARE DESIGNATED 'VULNERABLE' —ONE BECAUSE ITS HABITAT IS SHRINKING, THE OTHER BECAUSE IT IS POTENTIALLY UNDER THREAT FROM STOATS AND OTHER MAMMALS. 【A5】______ 100 YEARS AGO THERE WERE MORE THAN 5 MILLION NORTH ISLAND BROWN KIWIS.TODAY, THERE ARE PROBABLY AROUND 30,000 AND THE POPULATION IS DECREASING AT A RATE OF 6% A YEAR. ONLY THE LITTLE SPOTTED KIWI IS INCREASING BECAUSE OF SUCCESSFUL ATTEMPTS TO TRANSFER THE CREATURE TO PREDATOR-FREE OFFSHORE ISLANDS.THERE ARE FURTHER REASONS FOR HOP E.TRAPPING PREDATORS AND REARING BABY CHICKS FOR LATER RELEASE INTO THE WILD CAN HAVE A DRAMATIC EFFECT ON KIWINUMBERS; BUT IT WILL BE NECESSARY TO DO SO ON A LARGE SCAL E. IT WOULD BE TRAGIC IF NEW ZEALAND WERE TO LOSE ITS NATIONAL SYMBOL, THE KIW I.SURELY THE STRANGEST BIRD IN EXISTENCE, UNABLE TO FLY, IT SNIFFS OUT ITS FOOD WITH A REMARKABLY STRONG SENSE OF SMELL.ITS LEGS ARE POWERFUL AND MUSCULAR, FOR THE KIWI IS A BURROWER LIVING IN DENS—SOME SPECIES EVEN PREFERRING TUNNELS, YET ANOTHER SIMILARITY IT SHARES WITH SOME MAMMALS.BUT IT CANNOT SHARE ITS HABITAT WITH THEM WITHOUT EVENTUALLY LOSING THE BATTLE FOR SURVIVAL.

不受公有制经济的影响和制约

以生产资料私人占有和雇佣劳动为基础

是由社会主义初级阶段的生产力发展状况决定其存在的

是社会主义市场经济的组成部分

To a rock and mineral show.

To an opera at the concert hall.

To a movie at the student center.

To a popular music concert.

文化

消闲

体育

娱乐

ought to

has to

might

must

To a rock and mineral show.

To an opera at the concert hall.

To a movie at the student center.

To a popular music concert.

文化

消闲

娱乐

体育