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第1段
1 .<-NARRATOR:-> Listen to part of a lecture in a biology class.
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第2段
1 .<-FEMALE PROFESSOR:-> So, of course, many animals live in groups with others of their species.
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2 .And there are benefits to living together in groups...
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3 .it can help animals survive...
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4 .but there are also certain disadvantages.
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5 .So today we're going to talk about two disadvantages of living in groups for animals.
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6 .One disadvantage is that animals that live in groups may be more visible to predators.
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7 .If there's a big group of animals,
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8 .predators are more likely to spot them than they would an individual animal on its own.
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9 .So, sometimes, animals in groups may be more vulnerable to being captured by predators.
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10 .For instance, sardines...
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11 .really small fish...
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12 .swim in groups, and other, larger ocean animals, like some kinds of whales, eat them.
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13 .So, while a whale probably wouldn't notice one sardine,
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14 .it'd see a group of sardines very easily and thus be able to capture them for food.
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第3段
1 .Another disadvantage has to do with caring for the young.
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2 .In a large group, there are a lot of young animals around, and it can be difficult for animals to find or identify their own young...
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3 .and they may end up taking care of other animals' young instead.
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4 .So their own young may not get the care they need.
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5 .For example, some bats live in caves,
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6 .and with one type of bat,
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7 .millions of them live together in the same cave...
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8 .and with young bats so crowded together in the cave that
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9 .it's sometimes hard for a mother bat to find her babies.
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10 .So when a mother bat returns from finding food to feed her babies,
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11 .she might end up feeding the babies of another mother bat...
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12 .meaning her own babies don't get fed.
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