MGMAT CAT EXAM - Reading Comprehension - Desert Tortoise

[060504]

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.

Question: The passage mentions each of the following as known reasons that the desert tortoise is a threatened species EXCEPT

A) the flexibility of the desert tortoise’s shell in the first years of life
B) the low reproductive rate of desert tortoises
C) the loss of native plants in the desert tortoise habitat
D) predation by fellow reptiles
E) the transmission of disease from captive tortoises to the wild population

OA is C.

(C) CORRECT. Although the loss of native plants is mentioned, the passage stops short of saying it is a known reason that the desert tortoise is a threatened species. The last sentence of the third paragraph states that it is unknown "the loss of native plants ... may lessen the tortoise’s resistance to pathogens." The sentence goes on to acknowledge that tortoises do have other methods by which to procure water (that is, the loss of native plants may not actually harm tortoise’s much as far as water is concerned).

My question: I don't see how "Released captive tortoises can rapidly spread URTD into the wild population with devastating consequences" is more convincing as a known reason that the desert tortoise is a threaten species than "The loss of native plants to grazing livestock and invasive plant species, then, may lessen the tortoise’s resistance to pathogens." It is unclear to me that URTD actually CAUSES deaths in tortoises. If URTD is released to the "wild population", it can have "devastating consequences", but wouldn't we be reading a bit too much into that? Perhaps the devastating consequences will happen to ANOTHER species. Could someone please make this clearer?

[jnelson0612]

Good question! I think that we have to infer that the "devastating consequences" resulting from the URTD indicate a very big deal. To me, "devastating" implies a major, serious threat on a par with life and death.

Also, there's a good reason that C) isn't necessarily a problem. Let's look at this part of the passage again:
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.

This shows us that the loss of native plants is not actually a threat, since the turtles can compensate by digging the precipitation basins.

I think that you have to compare the two and ask yourself which is more threatening to the turtles: 1) loss of native plants even though turtles can compensate with basins, or 2) URTD which can have "devastating consequences".

Hope this helps! :-)