#25 - The dwarf masked owl, a rare migratory bird of prey

[srcline@noctrl.edu]

Hello

So the conclusion states : So unless steps are taken to re-establish the spiny cactus population, the dwarf masked owl will not make its home one the baja peninsula..

I diagrammed this as:

If owl makes its home on Baja peninsula steps must reestablish spin. cact. pop

Contra positive: steps not taken rest. spin cactus pop. owl wont make home on baja peninsula

So D is a mistaken reversal correct? But can someone explain why E is the correct answer , am I looking for an answer choice that mirrors the contra positive or the original conditional statement.

Thankyou
Sarah

[Robert Carroll]

Sarah,

Answer choice (D) is indeed the Mistaken Reversal of that connection. As such, it is not an assumption required by the argument, so it's a wrong answer. There is one thing you missed in the stimulus:

spiny cactus nesting sites

The lack of spiny cactus indicates that there are no suitable nesting sites for the owl, but the conclusion is that the owl will not make its winter home there. There is a gap between nesting sites and the winter home location. Thus, you need to connect those two things. This is why answer choice (E) is correct:

winter home nesting sites

and its contrapositive:

nesting sites winter home

Then you can say:

spiny cactus nesting sites winter home

And the conclusion of the argument is just the chain of conditionals above.

Robert Carroll

[LSAT2018]

So to understand your previous post correctly:
No Cactus Population → No Nesting Site
No Cactus Population → No Home on the Baja Peninsula
No Nesting Site → No Home on the Baja Peninsula
Home on the Baja Peninsula → Nesting Site (Contrapositive)

But the stimulus states there are no other suitable nesting sites for the dwarf masked owl on the Baja peninsula, but I don't think it was clear enough to represent this as No Cactus Population → No Nesting Site.

So would another way to approach this question involve taking the conclusion Home on the Baja Peninsula → Cactus Population, and identify an answer that would defend the necessary part, that the cactus population is suitable? Or am I just working backwards here?

[Adam Tyson]

I have to disagree with you, LSAT_2018. We are given that the spiny cacti are the only suitable nesting sites - there are no others. That can absolutely be diagrammed as:

Spiny Cacti Suitable Nesting Site

and the contra-positive:

Suitable Nesting Site Spiny Cacti

There is nothing in the stimulus that indicates, as you did in your question, that "the cactus population is suitable" is a necessary condition. That is a mistaken combination of a sufficient condition with a necessary condition into one condition.

Follow the steps Robert outlined here. The premises tell us that because the cacti are gone, there are no suitable nesting sites any more. The conclusion tells us the owls won't make their home there this winter. Connect the ideas of "no nesting sites" from the premises to the concept of "not make their home there" in the conclusion, and you will have your answer. Then, if you have any doubt, apply the Negation Technique to see whether the negated version of the answer in question ruins the argument.

Keep at it!

[Esquire123]

I kept answer choice A because I thought that its negated version seemed to attack the conclusion. Negated: “Some birds of pray other than the dwarf masked owl nest in the spiny cactus.” If there are other birds that nest on the same nesting grounds, couldn’t it be that they take over the nesting grounds and now there aren’t enough for the dwarf masked owls(dmo)? Which means the dmos don’t have anywhere to go? #help

[Luke Haqq]

Hi Esquire123!

It's great that you're applying the Assumption Negation technique. And you start to apply it correctly with (A) by negating it. In your explanation, however, it seems that you're adding an extra assumption that isn't in (A) or its negation.

Namely, what you suggest about other birds certainly makes sense--perhaps these other birds take over the spiny cactus as a nesting spot. Using your negation, if some birds of prey also use the spiny cactus as a nest, we don't know anything more about them, like how many of them there are or if there are enough of them to take over nesting sites. The answer choice (or its negation) would actually have to spell out additional possibilities like what you suggest.

But more centrally, that still doesn't get to the jump to a new variable in the conclusion within the stimulus. The first several sentences are discussing the owl's "nesting sites." The conclusion, though, drops mention of nesting sites and is instead about where the owl makes its winter "home." We don't know from the stimulus what the connection is between the owl's nesting site and its winter home. Are the two the same? Or is the owl's winter home different from its nesting site?

Answer choice (E) connects this gap. It states, "Suitable nesting sites must be present where the dwarf masked owl makes its winter home." If we negate this, we'd have "Suitable nesting sites [need not] be present where the dwarf masked owl makes its winter home." If that were true, the argument would fall apart because it doesn't follow that the owl won't make its winter home on the Baja just because suitable nesting grounds aren't present. The negation of (E) is saying that they could still make it their winter home there regardless.