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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.
The passage suggests that which of the following is true of the forest regions in New Brunswick sprayed with most anti-budworm pesticides other than Matacil?
选项 A、The fecundity of some flowering plants in those regions may have decreased to an even greater degree than in the regions where Matacil is used.
B、Insect mortality in those regions occurs mostly among the larger species of insects, such as bumblebees.
C、The number of seeds produced by common plant species in those regions is probably comparable to the number produced where Matacil is sprayed.
D、Many more plant species have become extinct in those regions than in the regions where Matacil is used.
E、The spruce budworm is under better control in those regions than in the regions where Matacil is sprayed.
答案A
解析 文中暗示，New Brunswick这片森林里喷洒了Matacil之外的杀虫剂会有什么效果?原文L19，Matacil杀虫剂的特点是least toxic，尚造成一些植物传粉受影响。由此可以推出，A正确，某些植物的有性生殖力可能比施用Matacil的地区更受影响。B、C都和这一段的论述毫无关系。D．extinct不正确，见第9题E选项。E．云杉毛虫将比使用Matacil的地域得到更好的控制。如果选择此选项，等于是做了一个assumption：毒性大的杀虫剂，效果也一定会好。显然此命题并不总为真。
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