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题库 / Prep2007E1-RC-61
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.
The passage suggests that tooth fractures in Pleistocene carnivores probably tended to occur less frequently
during periods in which more prey were available
at sites distant from the La Brea area
in older individual carnivores
in species that were not preserved as fossils
in species that regularly stole carcasses from other species
题目分析：
题目释义：
细节题目
考点：
推断（Inference）
旨在考察我们对文章的深度理解，以及逻辑推断能力。
这个题目定位在文章的最后部分内容中。作者在这部分内容中的意思是，牙齿的破坏实际上是因为捕猎者牙齿与猎物的骨骼接触所造成的。有可能有两个原因造成了这样的情况----猎物过少或尸体被偷（捕猎者过多）。注意题目问的是“less frequently”。
选项分析：
A选项：Correct. 在有更多的猎物的时期。有了更多的猎物，捕食者就不用和尸体的骨骼打交道了。所以牙齿的磨损就少了。
B选项：在远离La Brea的地区。作者在前文中已经批驳了“local bias”。地域性和牙齿的磨损程度没有关系。
C选项：在年龄较大的食肉动物中。文中没有提到动物的年龄问题。
D选项：在没有被保存成化石的物种中。文中没有提到这类信息。
E选项：在习惯性的偷盗其他物种的尸体的种群中。这个选项说反了。偷盗尸体意味着食用尸体，进而牙齿与骨骼更多的接触，导致牙齿更多的损坏。注意题目问的是“less frequently”。
原文 high frequently 原因是prey availability was low, 和 intense competition over kills 等
问题 less frequently 会怎样？
答：prey availability was high = during periods in which more prey were available
E：注意题目问的是“less frequently”！！！
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.
没看完文章导致定位错误。。。。一定要扫完全文再开始做题！！！
prey 猎物 predator 捕食者
定位最后一句话。
注意题目的问法：tooth fractures tended to occur less frequently 但是定位段的主语是thorough carcass consumption，就是说下面解释的原因反过来就是题目问的。
解释有：
1）prey availability was low
当食物少的时候，频率大。反过来即食物多的时候频率就小了(low frequency）
2）intense competition over kills or high rat of carcas theft 对猎物的过度竞争（食物不多导致争抢过多，而且吃的很干净这种会导致频率增加）反过来，比如食物很多的时候，不用争抢了，也不用吃的干干净净，只吃肉的话，就不会有那么大的破坏频率了
during periods in which more prey were available
less frequently
注意问的是less frequently 啊==
less frequently 问的是，没注意到这一点
结合最后作者给出explanation可知，extinct carnivores的牙齿碎裂比present-day carnivores的牙齿碎裂更加频繁，是因为行为不同导致，而行为不同的背后原因是以前猎物少捕食者多（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.）
carcass 屠宰后的畜体
这道题不能直接定位至原文某一句话 ，而是基于对文章后半部分的深度理解推论。
1. breakage frequencies in the extinct species were strikingly higher than those in the present-day species.
2. 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。
the answer need to refer to the two items in the passage.
作者在这部分内容中的意思是，牙齿的破坏实际上是因为捕猎者牙齿与猎物的骨骼接触所造成的。有可能有两个原因造成了这样的情况----猎物过少或尸体被偷（捕猎者过多）。注意题目问的是“less frequently”。
定位最后一句话。
注意题目的问法：tooth fractures tended to occur less frequently 但是定位段的主语是thorough carcass consumption，就是说下面解释的原因反过来就是题目问的。
解释有：
1）prey availability was low
当食物少的时候，频率大。反过来即食物多的时候频率就小了(low frequency）
2）intense competition over kills or high rat of carcas theft 对猎物的过度竞争（食物不多导致争抢过多，而且吃的很干净这种会导致频率增加）反过来，比如食物很多的时候，不用争抢了，也不用吃的干干净净，只吃肉的话，就不会有那么大的破坏频率了
为什么C选项不对呢？文章第二段第一句有说到“In considering possible explanations for this finding, the researchers dismissed demographic bias because older individuals were not overrepresented in the fossil samples.” 说明年老的个体没有“overrepresent”出牙齿破坏，所以C也可以是对的呀？
the researchers dismissed demographic bias because older individuals were not overrepresented in the fossil samples
排除了人口统计学上的区别（即年龄、种族这种）因为化石样本中的老龄个体没有多到有代表性。就是说不管老龄个体的结论是什么都不对，因为没有代表性，就无法判断频率是多是少
研究者排除了是年龄结构问题导致了灭绝物种 牙齿破损频率更高的可能性：因为化石中老龄个体没有更多地出现。（排除了该物种很大部分是老龄个体的可能，潜在暗示了老年个体牙齿更容易疏松）
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