托福阅读真题+题目+答案：Bird Extinctions on Islands

托福阅读真题+题目+答案：Bird Extinctions on Islands

Birds that evolved on islands where they had no natural predators are extremely vulnerable to the arrival of invasive animals. ▋This is illustrated by the extinction histories of island birds that evolved alongside native predators.▊ The islands of the Caribbean have suffered a rate of extinction and threat comparable to that on any other island group, but because they form a chain that in places lies close to two major continental landmasses, most support populations of native mammals and snakes. ▋As a result, native birds were generally better able to cope with introduced mammals when they arrived.▊ The ecological destruction initiated by early human settlers drove many birds to extinction. but in only a few cases was predation by invasive species the main cause

1.Paragraph 1 suggests that which of the following helps island birds to survive the introduction of invasive animals?

A.Living on islands that have a population of natural predators .

B.Having first become adapted to animal life on a continental mainland.

C.Inhabiting an island for a long time before the arrival of human settlers.

D.Living on islands that have many different species of birds.

Most bird extinctions in the world's oceans in the last 500 years have occurred predominantly on oceanic islands, the class of island that includes the smallest and most remote specks of land. which are usually the result of volcanic activity. The only continental islands (islands rising from continental landmasses beneath the sea) suffering extinctions are a small number lying off the coasts of Australia, Madagascar, and New Zealand, and some of these are as small and isolated as oceanic islands. Extinctions, then. have occurred primarily on the world's smallest and most isolated islands. whatever their geological origins. There are a number of reasons for expecting this to be the case. First, smaller islands can support only low populations and small populations are at greater risk of extinction. Second, small and isolated islands are less likely to support populations of native bird predators such as mammals or snakes, meaning that their native bird communities are less well prepared to coexist with introduced predators when they arrive. Remote islands are also likely to be free of insect disease carriers, and their residents are more susceptible to disease when it arrives, as they have poorer immune responses Third, remote islands may have been colonized later by people;perhaps counterintuitively, islands on which people settled first have suffered lower rates of extinction than islands that have been colonized in modern times. although there are plenty of exceptions Early human colonization might have led to the introduction to islands of relatively few predators giving the species on these island more time to adapt to living in their presence. Alternatively, it might be that early extinctions are under-recorded relative to later ones, and the pattern reflects the fact that the remaining species on islands colonized early are simply those that are better able to adapt.

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