In a national park located on an island, a herd of moose was increasing in number and threatening to destroy species ...

davisdaj@ on November 20, 2019

Im sorry, the answer choices appear different sometimes, why not this answer, E: The presence of wolves in an area tends to discourage other predators from moving into the area.

Ravi on November 29, 2019

@davisdaj@,

Great question. We're looking to resolve the paradox that's presented
in the stimulus. Moose were threatening native plants, so some wolves
were introduced. However, even though the wolves prospered, the moose
continued to grow in number.

What could explain this?

You'd think the wolves would shrink the moose population, but they
didn't. In order to do explain how this happened, we need an answer
that helps to show how the wolves could have actually helped the moose
population increase. Maybe the wolves ate animals that competed with
the moose for food or preyed on the moose.

Let's take a look at (E) and (C).

(E) says, "Moose that are too old to breed are just as likely to die
of natural causes as of attack by wolves."

The problem with (E) is that it's far too generalized to make any
difference in resolving the paradox. If moose that are too old to
breed are just as likely to die of natural causes as of by attack by
wolves, this doesn't tell us how likely this is. Additionally, this
answer choice is talking about a certain subset of moose, and we don't
know how large that subset is. Is it 1%? 50%? We don't know. Because
of the ambiguity with (E), we don't get any more information from it
that helps us explain the paradox, so we can get rid of this choice.

(C) says, "Wolves often kill moose weakened by diseases that probably
would have spread to other moose."

(C) works great. If the wolves are eating diseases moose that would
have spread the diseases to other moose, then this shows how
introducing wolves could help the moose population rise. The moose
wolves are killing would probably die from the disease anyway, but
since they're being killed by wolves, they're not spreading the
diseases to other moose, so fewer moose overall are getting the
diseases. The wolves are basically getting rid of the sick moose for
the healthy moose, allowing the healthy moose to stay disease-free, so
this is why (C) explains the paradox.

Hope this helps. Let us know if you have any other questions!

Konnor on July 21, 2020

do we just have to assume that "diseases" that spread to the moose are deadly?

shunhe on July 27, 2020

Hey there,

Thanks for the question! So take another careful look at (C), which says that wolves often kill moose weakened by diseases that probably would’ve spread to other moose. So we don’t need to assume that the diseases spread to the moose are deadly; we just need to know that the deer are weakened by the diseases, and then often killed by wolves which take advantage of the ensuing weakness/whatever to hunt the deer.

Hope this helps! Feel free to ask any other questions that you might have.