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第1段
1 .<-NARRATOR:-> Now listen to part of a lecture on this topic in a biology class.
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第2段
1 .<-MALE PROFESSOR:-> Imagine there's a group of mice living in a large field, and owls living nearby.
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2 .Now, owls eat mice¡ªso the number of mice there are at any given time depends upon the number of owls in the area...
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3 .um, because the more owls there are, the more mice get eaten, right?
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4 .Now, imagine one year,
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5 .there are more owls than usual.
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6 .Since there are more owls in the area to eat the mice,
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7 .what do you think will happen to the number of mice?
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8 .As you can imagine,
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9 .the number would drop... there'd be fewer mice.
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第3段
1 .As far as the other factor...
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2 .um, we can use rabbits to help understand this one.
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3 .Imagine a population of rabbits living in an area...
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4 .These rabbits usually start having their young at the end of winter,
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5 .after the cold winter weather is gone,
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6 .and they keep reproducing until the following winter, when they will stop again while the cold winter weather lasts.
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7 .But let's say this year, the winter season is very short...
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8 .and it uh, you know, starts getting warm much earlier than usual.
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9 .Since winter this year is so short,
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10 .the rabbits can start reproducing much earlier.
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11 .That means the rabbits in that area will have at least one extra reproductive cycle,
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12 .so, of course, one extra litter of baby rabbits.
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13 .So the number of rabbits in that area would increase a lot.
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