在这一系列周期性物种灭绝事件里，白垩纪晚期恐龙和菊石的灭绝仅仅是其中一个比较严重的事件。
The late Cretaceous extinction of the dinosaurs and ammonoids was just one of the more drastic in a whole series of such recurrent extinction episodes.
同样，加利福尼亚沿岸的红杉林也依靠周期性的火灾来减少物种间的竞争，并为植物的新生清理地面和树荫。
Likewise, the giant sequoia redwoods of coastal California rely on periodic fires to thin out the competition and clear the ground and canopy ready for new growth.
西南玻利维亚地区，位于3700米高度（超1200英尺），其物种都要能抵抗周期性发生的冰冻和干旱。
The varieties of this region of southwestern Bolivia -- at 3, 700 meters (over 12, 000 feet) -- are resistant to the freezes and droughts that periodically afflict it.
物种周期性大灭绝的理论本身依然是备受争议的，需要更多的证据以便进一步地论证。
The theory of periodic extinctions itself is still debated, with many insisting that more proof is needed.
虽然天体撞击的毁灭性不容置疑，但是没有证据表明彗星导致了地球物种周期性的大灭绝。
While there’s little doubt about the destructive power of cosmic impacts, there is no evidence that comets have periodically caused mass extinctions on our planet.
最近的科学分析不再支持地球上的物种灭绝有规律地周期性发生的观点，因此人们不再需要复仇女神的假设。
Recent scientific analysis no longer supports the idea that extinctions on Earth happen at regular, repeating intervals. Thus, the Nemesis hypothesis is no longer needed.
根据两种田鼠种群波动周期性、波动峰值出现的时间以及特定年份峰值的高度等特征，证明两物种波动均具有不稳定性。
Population fluctuations of both species were erratic in respect to annual occurrence, the time of the peak density of fluctuations within years, and the hight of peak the density a given year.
对小型哺乳动物种群数量周期性波动的外因调节假说进行介绍，概述了食物假说、捕食假说和复合因子假说的主要内容和研究进展。
This paper reviewed the new progress in the theory and hypothesis of population regulation in small mammals, focusing on the food hypothesis, predation hypothesis and multi-factorial hypothesis.
我认为他们已经很好地证明了这一点。周期性气候变化与动物种群中一再发生的我们习以为常的消亡之间存在相关性。
I think they've nicely demonstrated a correlation between periodic climate events and what we'd recognize as normal turnover in fauna that would happen over and over again, Barnosky said.
我认为他们已经很好地证明了这一点。周期性气候变化与动物种群中一再发生的我们习以为常的消亡之间存在相关性。
I think they've nicely demonstrated a correlation between periodic climate events and what we'd recognize as normal turnover in fauna that would happen over and over again, Barnosky said.
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