Clues to predator-prey dynamics

[joehurundas]

Source: GMATPREP2...Reading comprehension:

A recent study has provided clues to predator-prey dynamics in the late pleistocene era. Researchers compared the number of tooth fractures in present-day carnivores with tooth fractures in carnivores that lived 36,000 to 10,000 years ago that were preserved in the Rancho La Brea tar pits in Los Angeles. The breakage frequencies in the extinct species were strikingly higher than those in the present-day species.
In considering possible explanations for this findings, the researchers dismissed demographic bias because older individuals were not overrepresented in the fossils samples. They rejected preservational bias because a total absence of breakage in two extinct species demonstrated that the fractures were not the result of abrasion within the pits. They ruled out local because breakage data obtained from other pleistocene sites were similar to the La Brea data. The explanation they considered most plausible is behavioral differences between extinct and present-day carnivores - in particular, more contact between the teeth of predators and the bones of prey due to more thorough consumption of carcasses by the extinct species. Such thorough carcasses consumption implies to the researchers either that prey availability was low, at least seasonally, or that there was intense competition over kills and high rate of carcas theft due to relatively high predator densities.

(1) According to the passage, the researchers believe that the high frequency of tooth breakage in carnivores found at La Brea was caused primarily by

(A) the aging process in individual carnivores
(B) contact between the fossils in the pits
(C) poor preservation of the fossils after they were removed from the pits
(D) the impact of carnivores' teeth against the bones of other prey
(E) the impact of carnivores' teeth against the bones of other carnivores during fights over kills


(2) The primary purpose of the passage is to

(A) present several explanations for a well-know fact
(B) suggest alternative methods for resolving a debate
(C) argue in favor of a controversial theory
(D) question the methodology used in a study
(E) discuss the implications of a research findings


(3) The passage suggests that both fractures in pleistocene carnivores probably tended to occur less frequently

(A) during periods in which more prey were available
(B) at sites distant from the La Brea area
(C) in older individuals
(D) in species that were not preserved as fossils
(E) in species that regularly stole carcasses from other species

[mschwrtz]

You need to ask a question joehurundas. We won't just analyze every feature of an RC passage and its questions.

[kashif.sajjad]

7. The researchers’ conclusion concerning the absence
of demographic bias would be most seriously
undermined if it were found that
(A) the older an individual carnivore is, the more
likely it is to have a large number of tooth
fractures
(B) the average age at death of a present-day
carnivore is greater than was the average age at
death of a Pleistocene carnivore
(C) in Pleistocene carnivore species, older
individuals consumed carcasses as thoroughly
as did younger individuals
(D) the methods used to determine animals’ ages in
fossil samples tend to misidentify many older
individuals as younger individuals
(E) data concerning the ages of fossil samples
cannot provide reliable information about
behavioral differences between extinct
carnivores and present-day carnivores

The OA is D, but I want to know something about choices A & B.

For A: For older inviduals if the breakage frequency is higher, than wouldn't the higher frequency of breakage in the extinct species be attributable to the older age individuals in the extinct species and therefore attributable to demographics, the OA explanation says this choice actually strengthens, HOW?

For B, if the average age at death of a present-day
carnivore is greater than was the average age at
death of a Pleistocene carnivore, then higher age inviduals would tend to have a higher frequency of breakage, if this choice was true, then the impact should have been the opposite: the breakage frequency in the present day species should have been higher then the extinct species, but the OA explanation says that this choice has no bearing, it does have a bearing but in the opposite effect, doesn't it?

[tim]

you're misinterpreting the question. the question is how to undermine a claim that there is no demographic bias. your answer choices talk about consequences of having or not having age differences in the sample, but they don't address the question of whether we can undermine a claim of demographic bias. the best way to undermine the claim is to present evidence that ages cannot actually be determined for some reason..

consider: if i tell you happy chairs are more comfortable to sit on than sad chairs, what is the best way to undermine my claim? it is not to make any observation about the characteristics of happy chairs or sad chairs (like answers A and B); instead, it is to point out that there is no way to identify whether a chair is happy or sad (like answer D)..

[kvitkod]

in the question below the OA id D, but I believe that E is possible as well. Accroding to the passage, the competition, which includes fights as well, over kills was in palce.

Such thorough carcasses consumption implies to the researchers either that prey availability was low, at least seasonally, or that there was intense competition over kills and high rate of carcas theft due to relatively high predator densities.

(1) According to the passage, the researchers believe that the high frequency of tooth breakage in carnivores found at La Brea was caused primarily by

(A) the aging process in individual carnivores
(B) contact between the fossils in the pits
(C) poor preservation of the fossils after they were removed from the pits
(D) the impact of carnivores' teeth against the bones of other prey
(E) the impact of carnivores' teeth against the bones of other carnivores during fights over kills

[jnelson0612]

in the question below the OA id D, but I believe that E is possible as well. Accroding to the passage, the competition, which includes fights as well, over kills was in palce.

Such thorough carcasses consumption implies to the researchers either that prey availability was low, at least seasonally, or that there was intense competition over kills and high rate of carcas theft due to relatively high predator densities.

(1) According to the passage, the researchers believe that the high frequency of tooth breakage in carnivores found at La Brea was caused primarily by

(A) the aging process in individual carnivores
(B) contact between the fossils in the pits
(C) poor preservation of the fossils after they were removed from the pits
(D) the impact of carnivores' teeth against the bones of other prey
(E) the impact of carnivores' teeth against the bones of other carnivores during fights over kills

Here's the relevant part:
The explanation they considered most plausible is behavioral differences between extinct and present-day carnivores - in particular, more contact between the teeth of predators and the bones of prey due to more thorough consumption of carcasses by the extinct species. Such thorough carcasses consumption implies to the researchers either that prey availability was low, at least seasonally, or that there was intense competition over kills and high rate of carcas theft due to relatively high predator densities.

Be careful with making assumptions. That there is competition may mean that that a predator steals meat from another. We cannot assume that the predators fought over the prey just because there was competition.

Also, let's assume that "competition" does mean fighting. That is still not necessarily the reason, as the passage says it is EITHER that prey availability was low OR there was competition. Thus, the reason could have been that prey availability was low. However, the bolded part of the passage is described as the "most plausible" and is thus the correct answer.

[p111]

Hello Instructors,
I have a doubt reg:
59. The primary purpose of the passage is to
(A) present several explanations for a well-known fact
(B) suggest alternative methods for resolving a debate
(C) argue in favor of a controversial theory
(D) question the methodology used in a study
(E) discuss the implications of a research finding

I chose B, but word "debate" per me eliminates this(correct me if wrong)
I rejected OA E, as I didnt find "implications" of the finding in the passage. Passage is discussing basically the finding & the methodology used for it(2nd para). Where is it meant to imply or infer to anything ? Need help ..Tx

[RonPurewal]

Hello Instructors,
I have a doubt reg:
59. The primary purpose of the passage is to
(A) present several explanations for a well-known fact
(B) suggest alternative methods for resolving a debate
(C) argue in favor of a controversial theory
(D) question the methodology used in a study
(E) discuss the implications of a research finding

I chose B, but word "debate" per me eliminates this(correct me if wrong)
I rejected OA E, as I didnt find "implications" of the finding in the passage. Passage is discussing basically the finding & the methodology used for it(2nd para). Where is it meant to imply or infer to anything ? Need help ..Tx

Look at the end. Ironically, they are totally explicit about this"”they even use the word "implies" to introduce the implication:

Such thorough carcasses consumption implies to the researchers either that prey availability was low, at least seasonally, or that there was intense competition over kills and high rate of carcas theft due to relatively high predator densities.
... so, there you go.

One thing I'm not clear on here: You said you realized that "debate" rules out (B), but then you picked (B) anyway? I don't follow that.
Are you saying you've realized that now, after the fact, but didn't think of it when you were solving the problem?

[p111]

One thing I'm not clear on here: You said you realized that "debate" rules out (B), but then you picked (B) anyway? I don't follow that.
Are you saying you've realized that now, after the fact, but didn't think of it when you were solving the problem?

Yes Ron,
After I chose B & got the Q wrong, I went through forums to check it & there I got the idea.
If I am right, this particular Q is very careful into choosing words, as in every word in the answers is critical. Can you share your thoughts on how to handle such word of Qs esp. main idea Qs. As simply following the structure of passage wasn't sufficient in this Q. where the answer decider(word) was in the last few lines.

Thanks.

[RonPurewal]

One thing I'm not clear on here: You said you realized that "debate" rules out (B), but then you picked (B) anyway? I don't follow that.
Are you saying you've realized that now, after the fact, but didn't think of it when you were solving the problem?

Yes Ron,
After I chose B & got the Q wrong, I went through forums to check it & there I got the idea.
If I am right, this particular Q is very careful into choosing words, as in every word in the answers is critical. Can you share your thoughts on how to handle such word of Qs esp. main idea Qs. As simply following the structure of passage wasn't sufficient in this Q. where the answer decider(word) was in the last few lines.

Thanks.

This is not a "nitpicking words" situation. Choice (b) misses the entire point of the passage!
The passage is most definitely not intended to just "suggest a bunch of alternatives". That would imply that the passage would stop after merely laying out a few different hypotheses.
The problem is that, well, that's not what the passage does. After each hypothesis, it states clearly whether the researchers accepted or rejected it, and also states why. So, there's definitely an intention to arrive at one explanation here"”a purpose that's contradicted by choice (b), which implies that the intention is merely to spell out a few alternatives.

Choice (b) also ignores the whole discussion of what that explanation implies"”i.e., it ignores the entirety of the last paragraph. Not good.

My point here is that there is, and always will be, a HUGE difference between incorrect and correct answers on main idea questions. They will not write main-idea questions that require subtle nitpicking; the four wrong answers will be Wrong with a capital W.

If you think the differences are really small/nitpicky, then you are being too "academic" in your reading. If you read these things like real-world stuff"”magazine articles and the like"”then the differences will become a lot more clear.
(This is something that's true of CR and RC in general: If you read them like a normal person on planet earth, you'll do well. If you dissect them as you would "academic" passages, you're in for a world of hurt.)

[divineacclivity]

Ron,

I can't understand why answer choice A isn't right.
59. The primary purpose of the passage is to
(A) present several explanations for a well-known fact

I thought "either that prey availability was low, .., or that there was intense competition" - these are several explanations or a well-known fact that tooth fractures were more for old-age carnivorous than for present world carn. Please explain.

[jnelson0612]

Ron,

I can't understand why answer choice A isn't right.
59. The primary purpose of the passage is to
(A) present several explanations for a well-known fact

I thought "either that prey availability was low, .., or that there was intense competition" - these are several explanations or a well-known fact that tooth fractures were more for old-age carnivorous than for present world carn. Please explain.

Whenever you choose an answer for a reading comp question make sure that absolutely every word of the answer is acceptable.

Is the finding that ancient animals have more teeth fractures than modern animals do really a "well-known fact"? It's a well-known fact that the earth revolves around the sun, for example, but does this piece of info really qualify as a "well-known fact"? The GMAT would say no and they would point to these words as a reason that this answer is wrong.

This is why more vague, general answers are more likely to be correct on general reading comp questions. Please let me know if you need further clarification.

[ajaym8]

Hi,

Thanks for the explanation. However, my view is that the passage portion in bold is not relevant to the question. Question pertains to "tooth breakage in carnivores found at La Brea". Bold portion below is about comparison between extinct and present-day carnivores
The relevant portion of the passage I chose while attempting this question was :
"They ruled out local bias
because breakage data obtained from other
Pleistocene sites were similar to the La Brea data" which is reflected in option B.

Another thing, although of less importance is that OA is given as B (Source: gmatclub.com).

Please correct me if I am going wrong in my approach.
Thanks.


[

quote="jnelson0612"]

in the question below the OA id D,

but I believe that E is possible as well. Accroding to the passage, the competition, which includes fights as well, over kills was in palce.

Such thorough carcasses consumption implies to the researchers either that prey availability was low, at least seasonally, or that there was intense competition over kills and high rate of carcas theft due to relatively high predator densities.

(1) According to the passage, the researchers believe that the high frequency of tooth breakage in carnivores found at La Brea was caused primarily by

(A) the aging process in individual carnivores
(B) contact between the fossils in the pits
(C) poor preservation of the fossils after they were removed from the pits
(D) the impact of carnivores' teeth against the bones of other prey
(E) the impact of carnivores' teeth against the bones of other carnivores during fights over kills

Here's the relevant part:
The explanation they considered most plausible is behavioral differences between extinct and present-day carnivores - in particular, more contact between the teeth of predators and the bones of prey due to more thorough consumption of carcasses by the extinct species. Such thorough carcasses consumption implies to the researchers either that prey availability was low, at least seasonally, or that there was intense competition over kills and high rate of carcas theft due to relatively high predator densities.

Be careful with making assumptions. That there is competition may mean that that a predator steals meat from another. We cannot assume that the predators fought over the prey just because there was competition.

Also, let's assume that "competition" does mean fighting. That is still not necessarily the reason, as the passage says it is EITHER that prey availability was low OR there was competition. Thus, the reason could have been that prey availability was low. However, the bolded part of the passage is described as the "most plausible" and is thus the correct answer.[/quote]

[RonPurewal]

the answer to that question is definitely D. there's no doubt about that.

the question is about what researchers believed, so, i'm not sure why anyone is talking about "assumptions" here. the passage SAYS that there's one reason that the researchers themselves "considered most plausible".

"The explanation they considered most plausible is ... in particular, more contact between the teeth of predators and the bones of prey"
^^ that's pretty unambiguous.