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  3. Species interdependence in nature confers many benefits on the species involved , but it can also become a point of weakness whe

Species interdependence in nature confers many benefits on the species involved , but it can also become a point of weakness whe

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问题     Species interdependence in nature confers many benefits on the species involved , but it can also become a point of weakness when one species involved in the relationship is affected by a catastrophe. Thus, flowering plant species dependent on insect pollination, as opposed to self-pollination or wind pollination, could be endangered when the population of insect-pollinators is depleted by the use of pesticides.
    In the forests of New Brunswick, for example, various pesticides have been sprayed in the past 25 years in ef- forts to control the spruce budworm, an economically significant pest. Scientists have now investigated the effects of the spraying of Matacil, one of the anti-budworm agents that is least toxic to in- sect-pollinators. They studied Matacil’s effects on insect mortality in a wide variety of wild insect species and on plant fecundity, expressed as the percentage of the total flowers on an individual plant that actually developed fruit and bore seeds. They found that the most pronounced mortality after the spraying of Matacil occurred among the smaller bees and one family of flies, insects that were all important pollinators of numerous species of plants growing beneath the tree canopy of forests. The fecundity of plants in one common indigenous species, the red-osier dogwood, was significantly reduced in the sprayed areas as compared to that of plants in control plots where Matacil was not sprayed. This species is highly dependent on the insect-pollinators most vul- nerable to Matacil. The creeping dogwood, a species similar to the red-osier dogwood, but which is pollinated by large bees, such as bumblebees, showed no significant decline in fecundity. Since large bees are not affected by the spraying of Matacil, these results and weight to the argument that spraying where the pollinators are sensitive to the pesticide used decreases plant fecundity.
    The question of whether the decrease in plant fecundity caused by the spraying of pesticides actually causes a decline in the overall population of flowering plant species still remains unan- swered. Plant species dependent solely on seeds for survival or dispersal are obviously more vulnerable to any decrease in plant fecundity that occurs, whatever its cause. If, on the other hand, vegeta- tive growth and dispersal(by means of shoots or runners)are available as alternative reproductive strategies for a species, then decreases in plant fecundity may be of little consequence. The fe- cundity effects described here are likely to have the most profound impact on plant species with all four of the following characteristics: a short life span, a narrow geographic range, an incapacity for vegetative propagation, and a dependence on a small number of insect-pollinator species. Perhaps we should give special attention to the conservation of such plant species since they lack key factors in their defenses against the environmental disruption caused by pesticide use.
Which of the following best summarizes the main point of the passage?
选项 A、Species interdependence is a point of weakness for some plants, but is generally beneficial to insects involved in pollination.
B、Efforts to control the spruce budworm have had deleterious effects on the red-osier dogwood.
C、The used of pesticides may be endangering certain plant species dependent on insects for pollination.
D、The spraying of pesticides can reduce the fecundity of a plant species, but probably does not affect its overall population stability.
E、Plant species lacking key factors in their defenses against human environmental disruption will probably become extinct.
答案C
解析 主题题型：A．“generally beneficial to insects”从原文推不出来。B．“control the spruce budworm”是文中具体例子，不会是主题题型正确选项。C．正确。使用杀虫剂会危害一些依靠虫媒的植物。见文章首段概括以及后面的叙述。D．杀虫剂会减少一些植物有性生殖力，但对种群数量稳定没有影响。这是第三段一开始L50—55的内容，文章明确指出这种说法正确与否remain unanswered。E．“extinct”太过，文章只说有性生殖力受影响，未延伸到此种论断。
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