子机构
400-600-1123
logo GMAT备考资讯 答疑社区 GMAT公开课 提分课程

城市电话

申友-中心

免费咨询

咨询热线:

地址:
登录
注册

我的备考方案

获取方案

题库解析   >   其他题型   >  
    本题由hyman1提供
100次学习

Despite its 1989 designation as a threatened species, the desert tortoise has declined in numbers by ninety percent since the

1980s. Although federal protection made it illegal to harm desert tortoises or remove them from the southwestern North American deserts, this measure has been insufficient to reverse the species’ decline. The lack of recovery is partly due to the desert tortoise’s low reproductive potential. Females breed only after reaching fifteen to twenty years of age, and even then may only lay eggs when adequate forage is available. The average mature female produces only a few eggs annually. From these precious eggs, hatchlings emerge wearing soft shells that will take five years to harden into protective armor. The vulnerable young are entirely neglected by adult tortoises, and only five percent ultimately reach adulthood.

Predators are blamed for a majority of tortoise deaths; ravens alone are estimated to cause more than half of the juvenile tortoise deaths in the Mojave Desert. Tortoise eggs and juveniles can also fall prey to mammals and other reptiles. For protection from predators, as well as from desert temperature extremes, tortoises of all ages burrow into the earth. However, if rabbits and rodents are scarce, larger predators may exhume tortoises from their burrows, devouring even mature tortoises despite their hardened shells. Further, tortoises are susceptible to a wide range of pathogens. The population decline is partly due to upper respiratory tract disease (URTD), characterized by nasal and ocular discharge and palpebral edema. In 2006, more than 80 percent of captive desert tortoises had anti-mycoplasma antibodies, seropositive indication of the disease. Released captive tortoises can rapidly spread URTD into the wild population with devastating consequences.

Though desert tortoises are well adapted to arid habitats, and adults can survive a year without access to water, they rely heavily on moisture in the vegetation consumed in spring, when they surface from their hibernal dormancy. The loss of native plants to grazing livestock and invasive plant species, then, may lessen the tortoise’s resistance to pathogens, though the tortoises do also dig precipitation basins in the soil and linger near one when rain is impending.

The primary purpose of the passage is to

    A describe the lifecycle of a species

    B discuss the threats faced by a certain species

    C advocate research on a disease wide-spread among captive animals

    D evaluate potential solutions to a wildlife problem

    E criticize federal legislation protecting a certain species


登录申友留学,查看答案及解析
答案:
B

参与讨论

提交
吉祥物小蜜蜂
联系申友 全国免费咨询热线:400-600-1123

友情链接: 申友雅思 | 申友留学 | 申友GMAT官方微博 | 申友GMAT官方知乎机构账号

Copyright © 2020 All Right Reserved 申友教育 版权所有 沪ICP备17005516号-4 免责声明