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A small number of the forest species of lepidoptera (moths

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A small number of the forest species of lepidoptera (moths [#permalink] New post 24 Feb 2009, 14:15
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A small number of the forest
species of lepidoptera (moths and
butterflies, which exist as caterpillars
Line during most of their life cycle) exhibit
(5) regularly recurring patterns of population
growth and decline—such
fluctuations in population are known
as population cycles. Although many
different variables influence popula-
(10) tion levels, a regular pattern such as
a population cycle seems to imply a
dominant, driving force. Identification
of that driving force, however, has
proved surprisingly elusive despite
(15) considerable research. The common
approach of studying causes of
population cycles by measuring the
mortality caused by different agents,
such as predatory birds or parasites,
(20) has been unproductive in the case of
lepidoptera. Moreover, population
ecologists’ attempts to alter cycles
by changing the caterpillars’ habitat
and by reducing caterpillar popula-
(25) tions have not succeeded. In short,
the evidence implies that these insect
populations, if not self-regulating, may
at least be regulated by an agent more
intimately connected with the insect than
(30) are predatory birds or parasites.
Recent work suggests that this
agent may be a virus. For many
years, viral disease had been
reported in declining populations
(35) of caterpillars, but population ecologists
had usually considered viral
disease to have contributed to the
decline once it was underway rather
than to have initiated it. The recent
(40) work has been made possible by
new techniques of molecular biology
that allow viral DNA to be detected
at low concentrations in the environment.
Nuclear polyhedrosis viruses
(45) are hypothesized to be the driving
force behind population cycles in
lepidoptera in part because the
viruses themselves follow an infectious
cycle in which, if protected from
(50) direct sun light, they may remain
virulent for many years in the environment,
embedded in durable
crystals of polyhedrin protein.
Once ingested by a caterpillar,
(55) the crystals dissolve, releasing
the virus to infect the insect’s cells.
Late in the course of the infection,
millions of new virus particles are
formed and enclosed in polyhedrin
(60) crystals. These crystals reenter the
environment after the insect dies and
decomposes, thus becoming available
to infect other caterpillars.
One of the attractions of this
(65) hypothesis is its broad applicability.
Remarkably, despite significant differences
in habitat and behavior, many
species of lepidoptera have population
cycles of similar length, between eight
(70) and eleven years. Nuclear polyhedrosis
viral infection is one factor these
disparate species share.

Which of the following, if true, would most weaken the author’s conclusion in lines 25-
30?
A. New research reveals that the number of species of birds and parasites that prey
on lepidoptera has dropped significantly in recent years.
B. New experiments in which the habitats of lepidoptera are altered in previously
untried ways result in the shortening of lepidoptera population cycles.
C. Recent experiments have revealed that the nuclear polyhedrosis virus is present in
a number of predators and parasites of lepidoptera.
D. Differences among the habitats of lepidoptera species make it difficult to assess
the effects of weather on lepidoptera population cycles.
E. Viral disease is typically observed in a large proportion of the lepidoptera
population.
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Re: RC: Moths and Butterflies [#permalink] New post 25 Feb 2009, 08:12
...", population
ecologists’ attempts to alter cycles
by changing the caterpillars’ habitat
and by reducing caterpillar popula-
(25) tions have not succeeded....." hence B


icandy wrote:
A small number of the forest
species of lepidoptera (moths and
butterflies, which exist as caterpillars
Line during most of their life cycle) exhibit
(5) regularly recurring patterns of population
growth and decline—such
fluctuations in population are known
as population cycles. Although many
different variables influence popula-
(10) tion levels, a regular pattern such as
a population cycle seems to imply a
dominant, driving force. Identification
of that driving force, however, has
proved surprisingly elusive despite
(15) considerable research. The common
approach of studying causes of
population cycles by measuring the
mortality caused by different agents,
such as predatory birds or parasites,
(20) has been unproductive in the case of
lepidoptera. Moreover, population
ecologists’ attempts to alter cycles
by changing the caterpillars’ habitat
and by reducing caterpillar popula-
(25) tions have not succeeded. In short,
the evidence implies that these insect
populations, if not self-regulating, may
at least be regulated by an agent more
intimately connected with the insect than
(30) are predatory birds or parasites.
Recent work suggests that this
agent may be a virus. For many
years, viral disease had been
reported in declining populations
(35) of caterpillars, but population ecologists
had usually considered viral
disease to have contributed to the
decline once it was underway rather
than to have initiated it. The recent
(40) work has been made possible by
new techniques of molecular biology
that allow viral DNA to be detected
at low concentrations in the environment.
Nuclear polyhedrosis viruses
(45) are hypothesized to be the driving
force behind population cycles in
lepidoptera in part because the
viruses themselves follow an infectious
cycle in which, if protected from
(50) direct sun light, they may remain
virulent for many years in the environment,
embedded in durable
crystals of polyhedrin protein.
Once ingested by a caterpillar,
(55) the crystals dissolve, releasing
the virus to infect the insect’s cells.
Late in the course of the infection,
millions of new virus particles are
formed and enclosed in polyhedrin
(60) crystals. These crystals reenter the
environment after the insect dies and
decomposes, thus becoming available
to infect other caterpillars.
One of the attractions of this
(65) hypothesis is its broad applicability.
Remarkably, despite significant differences
in habitat and behavior, many
species of lepidoptera have population
cycles of similar length, between eight
(70) and eleven years. Nuclear polyhedrosis
viral infection is one factor these
disparate species share.

Which of the following, if true, would most weaken the author’s conclusion in lines 25-
30?
A. New research reveals that the number of species of birds and parasites that prey
on lepidoptera has dropped significantly in recent years.
B. New experiments in which the habitats of lepidoptera are altered in previously
untried ways result in the shortening of lepidoptera population cycles.
C. Recent experiments have revealed that the nuclear polyhedrosis virus is present in
a number of predators and parasites of lepidoptera.
D. Differences among the habitats of lepidoptera species make it difficult to assess
the effects of weather on lepidoptera population cycles.
E. Viral disease is typically observed in a large proportion of the lepidoptera
population.

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Re: RC: Moths and Butterflies [#permalink] New post 25 Feb 2009, 08:52
Here is what I am confused about

25) tions have not succeeded. In short,
the evidence implies that these insect
populations, if not self-regulating, may
at least be regulated by an agent more
intimately connected with the insect than
(30) are predatory birds or parasites.

So what is the conclusion in these 5 lines?

Pop Cycles are not completely self regulated and not caused by birds or insects.

The fact that alteration cycles have not succeeded is an evidence

While I agree that B attacks the evidence, I dont think it weakens the conclusion one way or the other.

With C it is saying that the virus from predators/birds is actually the cause. So Pop cycles are possibly caused by virus by birds/predators. The later part of the passage clearly establishes that virus is transmitted by birds and predators.

So why is C wrong and B is correct? is it because the NPV is not introduced in the passage by the lines of 25-30??
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Re: RC: Moths and Butterflies [#permalink] New post 25 Feb 2009, 09:04
I think it should be D.
A, C and E support the claim.
Between B and D, B tries to explain that it is the habitat and not the predator that regulates the population.

Hence, D.
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Re: RC: Moths and Butterflies [#permalink] New post 25 Feb 2009, 13:35
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icandy wrote:
Here is what I am confused about

25) tions have not succeeded. In short,
the evidence implies that these insect
populations, if not self-regulating, may
at least be regulated by an agent more
intimately connected with the insect than
(30) are predatory birds or parasites.

So what is the conclusion in these 5 lines?

Pop Cycles are not completely self regulated and not caused by birds or insects.

The fact that alteration cycles have not succeeded is an evidence

While I agree that B attacks the evidence, I dont think it weakens the conclusion one way or the other.

With C it is saying that the virus from predators/birds is actually the cause. So Pop cycles are possibly caused by virus by birds/predators. The later part of the passage clearly establishes that virus is transmitted by birds and predators.

So why is C wrong and B is correct? is it because the NPV is not introduced in the passage by the lines of 25-30??

25) tions have not succeeded. In short,
the evidence implies that these insect
populations, if not self-regulating, may
at least be regulated by an agent more
intimately connected with the insect than
(30) are predatory birds or parasites.

Which of the following, if true, would most weaken the author’s conclusion in lines 25-30?

--------------------------
Explanation:

A. New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years. ---> Irrelevant.

B. New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles. ---> The author mentions in the excerpt that there is some other agent that controls the insect population. He concludes this on the basis of info present in lines 15-25. But this option makes clear that there were still some untried ways, which actually resulted in some concrete findings (shortening of lepidoptera population cycles).

I think, nitya34 is also trying to convey the same reasoning.

C. Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera. ---> This may strengthen the argument by assuming virus as a more intimately connected regulatory agent. (Refer line 31: …..Recent work suggests that this agent may be a virus.....)

icandy: Can you please point to the line where it clearly establishes that virus is transmitted by birds and predators?

Anyways, IMO, even if it’s mentioned that the virus is transmitted by birds and predators, it’ll not be the correct answer because viruses are just piggybacking on birds and predators. Viruses are the actual agents not birds and predators.

So, I ruled out option C.

D. Differences among the habitats of lepidoptera species make it difficult to assess the effects of weather on lepidoptera population cycles. ---> Inconclusive. This option states that assessing the effect of weather (in case, it could have acted as an agent) on lepidoptera population cycles has proved to be a problematic task. As no results have been mentioned, we cannot conclude anything.

E. Viral disease is typically observed in a large proportion of the lepidoptera population. ---> Irrelevant.
--------------------------

I also go for option B.

Hope that helps.


Regards,
Technext
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Re: RC: Moths and Butterflies [#permalink] New post 25 Feb 2009, 13:43
Technext wrote:
icandy wrote:
Here is what I am confused about

25) tions have not succeeded. In short,
the evidence implies that these insect
populations, if not self-regulating, may
at least be regulated by an agent more
intimately connected with the insect than
(30) are predatory birds or parasites.

So what is the conclusion in these 5 lines?

Pop Cycles are not completely self regulated and not caused by birds or insects.

The fact that alteration cycles have not succeeded is an evidence

While I agree that B attacks the evidence, I dont think it weakens the conclusion one way or the other.

With C it is saying that the virus from predators/birds is actually the cause. So Pop cycles are possibly caused by virus by birds/predators. The later part of the passage clearly establishes that virus is transmitted by birds and predators.

So why is C wrong and B is correct? is it because the NPV is not introduced in the passage by the lines of 25-30??

25) tions have not succeeded. In short,
the evidence implies that these insect
populations, if not self-regulating, may
at least be regulated by an agent more
intimately connected with the insect than
(30) are predatory birds or parasites.

Which of the following, if true, would most weaken the author’s conclusion in lines 25-30?

--------------------------
Explanation:

A. New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years. ---> Irrelevant.

B. New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles. ---> The author mentions in the excerpt that there is some other agent that controls the insect population. He concludes this on the basis of info present in lines 15-25. But this option makes clear that there were still some untried ways, which actually resulted in some concrete findings (shortening of lepidoptera population cycles).

I think, nitya34 is also trying to convey the same reasoning.

C. Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera. ---> This may strengthen the argument by assuming virus as a more intimately connected regulatory agent. (Refer line 31: …..Recent work suggests that this agent may be a virus.....)

icandy: Can you please point to the line where it clearly establishes that virus is transmitted by birds and predators?

Anyways, IMO, even if it’s mentioned that the virus is transmitted by birds and predators, it’ll not be the correct answer because viruses are just piggybacking on birds and predators. Viruses are the actual agents not birds and predators.

So, I ruled out option C.

D. Differences among the habitats of lepidoptera species make it difficult to assess the effects of weather on lepidoptera population cycles. ---> Inconclusive. This option states that assessing the effect of weather (in case, it could have acted as an agent) on lepidoptera population cycles has proved to be a problematic task. As no results have been mentioned, we cannot conclude anything.

E. Viral disease is typically observed in a large proportion of the lepidoptera population. ---> Irrelevant.
--------------------------

I also go for option B.

Hope that helps.


Regards,
Technext


Technext,

Thanks for pointing out my figment of imagination. Thats what happens when one does not pay attention to the detail or gets caught up in the Question too much. No where it is mentioned that birds/predators transmit it. It just says that virus has cycles too and they hide in the protein. So apparently C is wrong.

Now B makes more sense. because the author is deriving the conclusion based on the evidence in the paragraph, the same conclusion will be weakened if a counter evidence is found.

Thanks for the good discussion Technext.
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Re: A small number of the forest species of lepidoptera (moths [#permalink] New post 17 May 2014, 11:35
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Re: A small number of the forest species of lepidoptera (moths   [#permalink] 17 May 2014, 11:35
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