RC - Passage on Desert Tortoise

[ankit26]

A question from the Desert Tortoise Passage that starts with

Despite its 1989 designation as a threatened species under the federal Endangered Species Act, the desert tortoise, Gopherus agassizii, has declined in numbers by ninety percent since the 1980s........................................................

It can be inferred from the passage that the desert tortoise mortality rate would be most likely to decrease if which of the following were true?

A) Desert tortoise burrows were cooler.
B) Male and female tortoises mated more frequently.
C) Adult tortoises provided better care for their young.
D) Forage plants were abundant in the habitat of the desert tortoise.
E) Rabbits were abundant in the habitat of the desert tortoise.

OA is E. However I chose C.

I am not convinced with the reason with which Choice C was rejected. Following is the explanation given for rejecting C.

(C) The vulnerability of hatchling and juvenile tortoises is mentioned, along with the fact that adult tortoises provide no care for their offspring. However, there is nothing in the passage to indicate that adult tortoises could have any positive effect on the survival rate of young tortoises by providing better care for them. It is entirely possible that adult tortoises are simply not equipped to protect the young from predators; feeding and caring for the hatchlings may have no effect on the juvenile survival rate.

The passage mentions that "The vulnerable young are entirely neglected by adult tortoises, and only five percent ultimately reach adulthood." This clearly indicates that if the adult provided better care, there was a chance that the young would survive.

Abundance of rabbits leading to survival of desert tortoise seems to me far stretched.

I am sorry, but would request an alternative explanation of the answer....

[StaceyKoprince]

On this test, when they ask us to infer, they are not asking us to draw what we would consider reasonable conclusions in the real world. They are actually asking us to restate some information already given in the passage, or to tell them something that MUST be true based on the info in the passage - no argument.

The text does not say that the babies are neglected and as a result only 5% reach adulthood. Unless it actually says that, you can't make the assumption, because it is not 100% true that better care would cause more to reach adulthood. It's very likely, I agree, but I can still argue that it might not be true.

As for the correct answer, here's the relevant text in the passage:
"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 mammalian predators may dig tortoises out of their burrows, devouring even mature tortoises despite their hardened shells."

This tells us:
IF rabbits are scarce then predators may dig out the tortoises and eat them.

There is an actual causal connection here. We must accept this as true. And if it is true that predators dig up tortoises and eat them precisely because rabbits are scarce, then it must also be true that if there are more rabbits, predators won't be digging up as many tortoises and eating them. And if not as many tortoises are being eaten, then the mortality rate would decrease. I can't argue that it might not be true - I have to accept the text in the passage as true. And everything else follows.

[Guest]

thanks Stacey.....that helps....

[StaceyKoprince]

you're welcome!

[Gaurav]

"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 mammalian predators may dig tortoises out of their burrows, devouring even mature tortoises despite their hardened shells."


Stacey ... Going by the same logic you have given for C being incorrect .... E also does NOT neccesarily have to be true ...

The passage says (as per the bold text) .. If A then B ...

You cannot assume If NOT A then NOT B (Which is what choice E does) ... You can only say that If NOT B then NOT A ....

[StaceyKoprince]

Ah, you're using formal logic rules. Nice! But, actually, this is an "if not B, then not A" setup. The wording of the question and answers just messed you up.

Premise:
If rabbits are scarce, then predators may dig up tortoises and eat them.

The questions asks what would cause mortality to decline, so the wording should be: IF mortality is declining, what must be true? The question is what's given - the answer is what we must find.

So, given the premise above, if the predators are NOT digging up and eating the tortoises (whichi means the mortality rate is decreasing), then rabbits must NOT be scarce. If NOT B, then NOT A. :)

[Guest]

ah.. that way ... now i see it .. thanks for the explamation

[StaceyKoprince]

You're welcome! It can be a little tough to apply formal logic rules to questions of this type - sometimes it's fine, but sometimes it's hard to tell how to set things up.

[ThomasqG569]

Dear all, Dear Stacey,

i chose E because the text clearly states following:"redators are blamed for a majority of tortoise deaths"

So basically I thought, that predators must have the highest influence on the mortality rates

Conclusion: If the predators have other food resources, they wont kill Desert Tortoise. (Kinda extreme but that is just my basic idea)

Can you confirm my logic?
Many thanks

[RonPurewal]

I don't see the passage text here.

Per the forum rules, please post the entire text of the passage. Thanks. (You can just copy and paste it, so very little effort will be involved.)

[kundatta]

I understand why the answer is E. I'm just posting the passage in case there are future questions/discussions. (Which I'm sure there will be) Took me a good 5 min of searching to figure it out in my review!

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.

[tim]

Thanks. Let us know if there are any further questions on this topic.