原文已被隐藏，你可用 快捷键 - 或点击 显示原文 按钮来查看原文
第1段
1 .<-NARRATOR:-> Listen to part of a lecture in an environmental science class.
请听环境科学课上的部分内容。
第2段
1 .<-FEMALE PROFESSOR:-> Roads-paved roads-are everywhere and sometimes seem like part of the natural landscape.
道路和人行道随处可见，有时候它们就像自然风景中不可分割的一部分。
2 .But of course, roads are not part of nature and, in fact,
不过，当然啦，道路并不是自然的一部分，而且事实上，
3 .road construction can have harmful effects on the environment
道路建设对环境会产生有害影响，
4 .and seriously impact both animal life and plant life.
对动植物生命都会构成严重威胁。
第3段
1 .One harmful environmental effect of roads
道路对环境的其中一个有害影响就是：
2 .is that they contribute to the movement of plant species from one area to another.
它们会导致植物种群从一个地区迁移到另一个地区。
3 .This causes problems for existing plants, plants already growing in that area...
这会给已经存在的植物，即已经生长在该地区的植物带来麻烦，
4 .because when a new plant species gets introduced into an area where it wasn't growing before,
因为当一个新的植物品种被引入某个新地区时，
5 .the new plants compete for resources with the existing plant life.
这个新品种的植物便会和现有植物抢夺资源。
6 .For example, this happened in California with a weed called the yellow starthistle.
比如这种生长在加利福尼亚州的植物---黄色矢车菊。
7 .What happened was, the starthistle's seeds got stuck to the tires of cars driving down the road,
事情是这样的：车辆驶过道路时，车胎上粘着了矢车菊的种子，
8 .and the seeds were distributed to new areas.
而这些种子便随着汽车被传播到了新的地区。
9 .This put the starthistle in competition for natural resources-like water-
这就使得矢车菊和当地原生植物竞争起了自然资源，
10 .with the original plant life of the area.
比如水资源。
11 .That made it harder for the native plants to survive.
当地植物的生存也随之变得更加困难。
第4段
1 .Also, roads,
另外，道路
2 .especially major highways,
尤其是主要的高速公路，
3 .can act as barriers
可能会充当屏障把动物栖息地
4 .and divide up an animal's habitat into smaller ones where there's not enough food to support the population.
分割成小片区域，而在这些小片区域里动物难以获得足够食物。
5 .These busy highways,
这些高速公路大多十分繁忙，
6 .with cars speeding past day and night,
车辆不分日夜地快速驶过，
7 .act like boundaries that animals are afraid to cross,
就像动物们害怕穿过的边界线一样。
8 .so they sometimes get shut in on a small piece of land
所以它们有时便被困在那小片区域里，
9 .where there isn't enough food to support them.
根本找不到充足的食物。
10 .This is a serious problem for animals that need access to large expanses of land to look for food.
对于需要进入广阔区域寻找食物的动物来说，问题十分严峻。
11 .For example, there are these foxes,
比如，有一种狐狸
12 .called kit foxes,
名为墨西哥狐的狐狸，
13 .that live in the southwestern United States.
生活在美国西南部
14 .They hunt small animals like mice and squirrels,
它们以老鼠和松鼠等小型动物为食，
15 .which are spread out over large areas of open grasslands.
而这些小型动物多分布在空旷草地的广阔区域。
16 .And now, because of these roads,
而现在，由于这些道路的影响，
17 .the kit fox population has declined significantly...
墨西哥狐的数量急剧减少，
18 .because now they don't get enough food.
因为它们现在无法获得足够的食物。