TPO75阅读真题+题目+答案下载：Clutch Size in Birds

TPO75阅读真题+题目+答案下载：Clutch Size in Birds

Each year the emperor penguin lays one egg, the pigeon lays one or two eggs, the gull typically lays three eggs, the Canada goose four to six eggs, and the American merganser ten or eleven eggs. What determines clutch size in birds? The ultimate factors that determine clutch size are the requirements for long-term (evolutionary) survival. Clutch size is viewed as an adaptation under the control of natural selection.

1.The word "ultimate" in the passage is closest in meaning to

A fundamental

B characteristic

C various

D immediate

Natural selection will favor those birds that leave the most descendants to future generations. At first thought we might hypothesize that natural selection favors a clutch size that is the physiological maximum the bird can lay. We can test this hypothesis by taking eggs from nests as they are laid. When we do this, we find that some birds, such as the common pigeon, are determinate layers; they lay a given number of eggs, no matter what. The pigeon lays two eggs, if you take away the first, it will incubate the second egg only. If you add a third egg, it will incubate all three. But many other birds are indeterminate layers; they will continue to lay eggs until the nest is "full." If eggs are removed once they are laid, these birds will continue laying. When this subterfuge was used on a mallard female, she continued to lay one egg per day until she had laid 100 of them. Evidence from other, similar experiments suggests that most birds under normal circumstances do not lay their physiological limit of eggs but that ovulation is stopped long before this limit is reached.

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

A Experimental evidence suggests that for most birds,the physiological limits of egg production depend on the circumstances.

B Experimental evidence suggests that most birds are physiologically capable of laying more eggs than they normally do.

C Most experiments yield similar evidence about the extent to which egg laying is normally determined by the physiological limits of egg production.

D Although some experiments suggest that birds lay as many eggs as they can, other, similar experiments suggest that this is not true for most birds.

3.According to paragraph 2, what is the difference between determinate layers and indeterminate layers?

A Determinate layers typically have much smaller clutches than indeterminate layers do.

B Determinate layers lay fewer eggs than they are capable of incubating, whereas indeterminate layers typically lay more eggs than they are capable of incubating.

C Indeterminate layers typically build larger nests for their eggs than determinate layers do.

D The number of eggs produced by an indeterminate layer depends on the circumstances, whereas the number of eggs produced by a determinate layer does not

The British ornithologist David Lack was one of the first ecologists to recognize the importance of evolutionary thinking in understanding adaptations in life history traits. ⬛ In 1947 Lack put forward the idea that clutch size in birds was determined by the number of young that parents can provide with food. ⬛ If his hypothesis is correct, the total production of young ought to be highest at the normal clutch size. ⬛ And if one experimentally increased clutch size by adding eggs to nests, increased clutches should suffer greater losses because the parents could not feed the extra young in the nest. ⬛

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