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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2024-01-13  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] It can be inferred that which of the following is true of plant fecundity as it is defined in the passage?
选项 A、A plant’s fecundity decreases as the percentage of unpollinated flowers on the plant increases.
B、A plant’s fecundity decreases as the number of flowers produced by the plant decreases.
C、A plant’s fecundity increases as the number of flowers produced by the plant increases.
D、A plant’s fecundity is usually low if the plant relies on a small number of insect species for pollination.
E、A plant’s fecundity is high if the plant can reproduce quickly by means of vegetative growth as well as by the production of seeds.
答案 A
解析 哪一个符合文中对植物有性生殖力的记叙?A．正确。此能力当植物的未受粉花比率增高时将降低，见原文L23—26“fecundity”一词的定义：指一植物的花真正发展为果实、种子的比率，未受粉花比率增高，此能力当然降低。B．开花少，此能力下降。不一定，关键看受粉情况。C．与B同理。D．若仅依赖少数几种昆虫授粉，此能力就低。关键看这种传粉是否受到了影响，若没有，就不会低。E．荒谬。fecundity指的有性生殖力，一个植物vegetative growth能力的高低对它没有影响。
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