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A classic series of experiments to determine the effects of overpopulation on communities of rats was conducted by a psychologist, John Calhoun. In each experiment, an equal number of male and female adult rats were placed in an enclosure. The rat populations were allowed to increase. Calhoun knew from experience approximately how many rats could live in the enclosures without experiencing stress due to over crowding. He allowed the population to increase to approximately twice this number. Then he stabilized the population by removing offspring that were not dependent on their mothers. At the end of the experiments, Calhoun was able to conclude that overcrowding causes a break down in the normal social relationships among rats, a kind of social disease. The rats in the experiments did not follow the same patterns of behavior as rats would in a community without overcrowding.
The females in the rat population were the most seriously affected by the h
A. Dominant males had adequate living space.
B. Dominant males were not as seriously affected by overcrowding as the other rats.
C. Dominant males attacked weaker rats.
D. The strongest males are always able to adapt to bad conditions.
Text 1
A classic series of experiments to determine the effects of overpopulation on communities of rats was conducted by a psychologist, John Calhoun. In each experiment, an equal number of male and female adult rats were placed in an enclosure. The rat populations were allowed to increase. Calhoun knew from experience approximately how many rats could live in the enclosures without experiencing stress due to over crowding. He allowed the population to increase to approximately twice this number. Then he stabilized the population by removing offspring that were not dependent on their mothers. At the end of the experiments, Calhoun was able to conclude that overcrowding causes a break down in the normal social relationships among rats, a kind of social disease. The rats in the experiments did not follow the same patterns of behavior as rats would in a community without overcrowding.
The females in the rat population were the most seriously affected by the h
A. when it was double the number that could live in the enclosure without stress
B. by removing young rats
C. so that there was a constant number of adult rats in the enclosure
D. All of the above are correct
Climate, more than any other single factor, determines the distribution of life on earth. Climatic boundaries establish the limits within which organisms can survive. Plants, even more than animals, must be well adapted to climate in order to survive. They cannot move about or take shelter but must be equipped to endure whatever weather conditions. In the cold north pole, for example, low growing mosses(苔,藓) all hug the ground for shelter from icy winds.
Animals, despite their ability to move about and find shelter, are just as much influenced by climate as plants are. Creatures such as the camel and the penguin are so highly specialized that they have an extremely limited distribution. Others, such as bears, are flexible enough to adapt to a broad range of climates. Ocean-dwelling organisms are just as sensitive to climate changes in this temperature and salinity as land animals.
Human beings are among the least specialized of all animals and live almost
A. Penguins.
B. Camel
C. Bears.
D. Mosses.
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