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  3. Species interdependence in nature confers many benefits on the species invol

Species interdependence in nature confers many benefits on the species invol

游客2025-02-25  25
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. [br] Which of the following assumptions most probably underlies the author’s tentative recommendation in lines 72 — 77?
选项 A、Human activities that result in environmental disruption should be abandoned.
B、The use of pesticides is likely to continue into the future.
C、It is economically beneficial to preserve endangered plant species.
D、Preventing the endangerment of a species is less costly than trying to save an already endangered one.
E、Conservation efforts aimed at preserving a few well-chosen species are more cost-effective than are broader-based efforts to improve the environment.
答案 B
解析 下面哪一个设想会加强作者的建议?见L72—77，作者建议为：应给予一些有性生殖力易受杀虫剂影响的植物以特别关照。我们可以把每一个选项取非，看哪一个结果会让上述结论不能做出来。∴B正确，杀虫剂的使用会继续下去。A、C、D、E都和这个结论无关。
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