-
marathi478
- Newbie | Next Rank: 10 Posts
- Posts: 1
- Joined: Fri Apr 22, 2011 3:54 am
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 and 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
finding, the researchers dismissed demographic bias
because older individuals were not overrepresented
in the fossil 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 bias because breakage data
obtained from other Pleistocene sites were similar
to the La Brea data. The explanation they consider
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 carcass consumption implies to
the researchers either that prey availability was
low, at least seasonally, or that there was intense
competition over kills and a high rate of carcass
theft due to relatively high predator densities.
Q7. 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?
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 and 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
finding, the researchers dismissed demographic bias
because older individuals were not overrepresented
in the fossil 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 bias because breakage data
obtained from other Pleistocene sites were similar
to the La Brea data. The explanation they consider
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 carcass consumption implies to
the researchers either that prey availability was
low, at least seasonally, or that there was intense
competition over kills and a high rate of carcass
theft due to relatively high predator densities.
Q7. 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?
