Despite its 1989 designation as a threatened species, the desert tortoise has declined in numbers by ninety percent since the
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 passage implies that a mature female desert tortoise
A has little contact with its offspring after birth
B might produce only one surviving offspring each decade
C has a softer shell than a mature male desert tortoise
D produces fewer offspring than a mature male desert tortoise
E reached reproductive maturity at a later age than a male desert tortoise
- Many Runagian senior citizens are no better off financially now than they were before the increase.The phrase “better off” is closest in meaning to________?
- The word "accidental" is closest in meaning to___________ ?
- Who can it be? I’ m quite ____ a loss to guess．
- The number of people flying first class on domestic flights rose sharply in 1990, doubling the increase of the previous year.
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