【OG24-533题】It can be inferred from the passage that the mortality caused by agents such as predatory birds or parasites was measured in an attempt to_mofa留学圈mofaGRE在线题库系统_GRE在线搜题_GRE题库解析_GRE真题机经_GRE课程_GRE培训机构

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A small number of the forest species of lepidoptera (moths and butterflies, which exist as caterpillars during most of their life cycle) exhibit regularly recurring patterns of population growth and decline—such fluctuations in population are known as population cycles. Although many different variables influence population levels, a regular pattern such as a population cycle seems to imply a dominant, driving force. Identification of that driving force, however, has proved surprisingly elusive despite considerable research. The common approach of studying causes of population cycles by measuring the mortality caused by different agents, such as predatory birds or parasites, has been unproductive in the case of lepidoptera. Moreover, population ecologists’ attempts to alter cycles by changing the caterpillars’ habitat and by reducing caterpillar populations have not succeeded. In short, the evidence implies that these insect populations, if not self-regulating, may at least be regulated by an agent more intimately connected with the insect than are predatory birds or parasites.

Recent work suggests that this agent may be a virus. For many years, viral disease had been reported in declining populations of caterpillars, but population ecologists had usually considered viral disease to have contributed to the decline once it was underway rather than to have initiated it. The recent work has been made possible by new techniques of molecular biology that allow viral DNA to be detected at low concentrations in the environment. Nuclear polyhedrosis viruses are hypothesized to be the driving force behind population cycles in lepidoptera in part because the viruses themselves follow an infectious cycle in which, if protected from direct sunlight, they may remain virulent for many years in the environment, embedded in durable crystals of polyhedrin protein. Once ingested by a caterpillar, the crystals dissolve, releasing the virus to infect the insect’s cells. Late in the course of the infection, millions of new virus particles are formed and enclosed in polyhedrin crystals. These crystals reenter the environment after the insect dies and decomposes, thus becoming available to infect other caterpillars.

One of the attractions of this hypothesis is its broad applicability. Remarkably, despite significant differences in habitat and behavior, many species of lepidoptera have population cycles of similar length, between eight and 11 years. Nuclear polyhedrosis viral infection is one factor these disparate species share.

It can be inferred from the passage that the mortality caused by agents such as predatory birds or parasites was measured in an attempt to

develop an explanation for the existence of lepidoptera population cycles identify behavioral factors in lepidoptera that affect survival rates identify possible methods for controlling lepidoptera population growth provide evidence that lepidoptera populations are self-regulating determine the life stages of lepidoptera at which mortality rates are highest

正确答案： A

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文章大意逻辑
文章开篇指出一小部分森林鳞翅目物种（飞蛾和蝴蝶，大部分生命周期以毛毛虫形态存在）存在定期的种群数量增长和下降模式，即种群周期。虽然很多变量影响种群水平，但这种规律模式似乎意味着有主导驱动因素，然而确定该因素很困难。接着说明研究种群周期原因的常见方法（测量捕食性鸟类或寄生虫等造成的死亡率）在鳞翅目方面没有成果，改变毛毛虫栖息地和减少其数量来改变周期的尝试也未成功，暗示这些昆虫种群若不是自我调节，也至少由与昆虫联系更紧密的因素调节。最后提出最近研究表明这个因素可能是病毒，过去种群生态学家对病毒作用看法不同，新技术让检测低浓度病毒DNA成为可能，还介绍了多角体病毒被假设为驱动因素的原因及感染过程。 文章类型及逻辑简图
文章类型：新旧观点对比 逻辑简图 Old view：Many variables influence population levels, but identifying the dominant driving force of lepidoptera population cycles is elusive. Common approaches like measuring mortality by predators or parasites are unproductive, and attempts to alter cycles fail. New view：Recent work suggests a virus may be the driving force. New techniques allow viral DNA detection. Polyhedrosis viruses are hypothesized as the driver due to their infectious cycle. 做题方法及问题类型
这是一道推断题，通过定位到文中“the common approach of studying causes of population cycles by measuring the mortality caused by different agents, such as predatory birds or parasites”相关内容，根据上下文逻辑进行推断。 选项分析
A选项：测量捕食性鸟类或寄生虫等造成的死亡率，是为了解释鳞翅目种群周期的存在。从文章逻辑来看，研究种群周期原因的常见方法就是测量这些因素造成的死亡率，所以测量死亡率是为了解释种群周期存在，该项正确。 B选项：文中未提及测量死亡率是为了识别影响鳞翅目存活率的行为因素，排除。 C选项：文章未表明测量死亡率是为了确定控制鳞翅目种群增长的可能方法，排除。 D选项：文中没有信息表明测量死亡率是为了提供鳞翅目种群自我调节的证据，排除。 E选项：测量死亡率不是为了确定鳞翅目死亡率最高的生命阶段，排除。

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