That a population crash occurs as a result of natural enemies or disease.

布朗称：“想让小丑瓢虫种群数量骤减，必须有天敌介入或者疾病发生。”

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This time, he focused on what he calls the single most risky demographic on the road? Teenage boys? Whose crash rate is twice that of the general population.

这次，他把焦点集中在他所称的——路上最可能出风险的个体：男性多动症青少年，因为他们出事故的概率是普通人群的两倍。

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Something similar happened to the region's herring population, which took three years to crash after the Alaska spill and hasn't recovered yet.

类似的情况在青鱼的数量上也体现了出来，阿拉斯加原油泄漏花了三年的时间才溶解，然而该海区尚未恢复。

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"That the population is so high that there will be a major population crash, that we will run out of food unless we change our ways, this just turns out not to be truth."

VOA: standard.2010.01.23

Here, the heroine of the previous films, Ripley (Sigourney Weaver), crash-lands on a godforsaken planet whose population consists of a couple of dozen mean-looking convicts running some sort of dilapidated foundry.

NEWYORKER: Alien 3

Meanwhile, the sea-urchin population increased steeply until its discovery by the Japanese sushi industry led to heavy harvesting and a subsequent crash in the early 1990s.

ECONOMIST: Lobsters in Maine