Reading Comprehension

A basic principle of ecology is that population
size is partly a reflection of available food
resources. Recent experiments suggest that the
relationship is more complex than formerly
thought. Specifically, the browsing of certain
rodents appears to trigger chemical reactions in
food plants which, in turn, affect the size of the
rodent populations. Two examples of such regulation
have been reported.

Berger has demonstrated the power of a naturally
occurring chemical called 6-MBOA to stimulate
reproductive behavior in the mountain vole,
a small mouse-like rodent. 6-MBOA forms in
young grass in response to browsing by voles.
Berger experimented by feeding oats coated with
6-MBOA to non-breeding winter populations of
voles. After three weeks, she found a high incidence
of pregnancy among females. Since the
timing of reproduction is crucial to the short-lived
vole in an environment in which the onset of vegetative
growth may be considerably delayed, the
phytochemical triggering of reproductive behavior
represents a significant biological adaptation.

In an example reported by Bryant, plants
appear to have developed a phytochemical
defense against the depredations of snowshoe
hares in Canada. Every ten years, for reasons
that are unclear, the hare population swells. The
result is overbrowsing of certain deciduous trees
and shrubs. Bryant found that trees favored by
the hare produce young shoots high in terpene
and phenolic resins, which discourage hare
browsing. After treating non-resinous willow twigs
with resinous extracts and placing treated and
untreated samples at hare feeding stations,
Bryant found that samples containing at least
half of the resin concentration of natural twigs
were untouched. The avoidance of resinous
shoots, he concludes, may play a role in the
decline of the hare population to normal levels.

Both of these reports suggest areas for further
research. For example, data should be
reviewed to determine if periodic population
explosions among lemmings (another small
rodent living in a northern environment) occur
during years in which there is an early onset of
vegetative growth; if so, a triggering mechanism
similar to that prompted by the vole may be
involved.


Q1
The author provides specific information to answer which of the following questions?
(A) What factors other than food supply affect the population size of rodents?
(B) Why is the timing of the voles'reproductive effort important?
(C) Are phytochemical reactions found only in northern environments?
(D) How does 6-MBOA trigger reproductive activity in the mountain vole?
(E) What are the causes of the periodic increase in the snowshoe hare population?

OA: B
I agree on OA but whats wrong with A. A is there at the end of 1st paragraph.

Q2
It can be inferred that the study of lemmings proposed by the author would probably
(A) strengthen the conclusions of Bryant
(B) cast doubt on the conclusions of Bryant
(C) support the specific findings of Berger
(D) provide evidence as to whether Berger's conclusions can be generalized
(E) disprove common beliefs about the relationship between population size and food supply

OA: D
I am confused over C and D. I believe that It provides an evidence, which support Berger'statement.

hi akhilesh

i am not expert but just to understand the passage and your questions

Q1. Since the timing of reproduction is crucial to the short-lived
vole in an environment in which the onset of vegetative
growth may be considerably delayed, the
phytochemical triggering of reproductive behavior
represents a significant biological adaptation.

hence the answer is B.

i am not agree with A

A basic principle of ecology is that population size is partly a reflection of available food resources.Recent experiments suggest that the relationship is more complex than formerly thought. Specifically, the browsing of certain rodents appears to trigger chemical reactions in food plants which, in turn, affect the size of the rodent populations

the above passage clearly suggest that they wan to search the food supply affects the the population size of rodents.
but A tell opposite to this.


Q2. D is the correct answer

Berger has demonstrated the power of a naturally occurring chemical called 6-MBOA to stimulate reproductive behavior in the mountain vole,

if periodic population explosions among lemmings (another smallrodent living in a northern environment) occur
during years in which there is an early onset of vegetative growth; if so, a triggering mechanism
similar to that prompted by the vole may be involved.

provide evidence as to whether Berger’s conclusions can be generalized

Hi Pradeep,

I got Q1 but still I have doubt in Q2.

In last paragraph, author mentioned a conditional statement. Is this a generalization?

yes i think so.
giving examples leads to generalization. since the phenomena is true or common in all creatures like vole and lemmings then they generalize this phenomena.

i hope some experts will come forward to explain more.