Ecosystem Resilience
An ecosystem is a local environment with its complex community of organisms functioning together as a unit. An ecosystem can be damaged by natural disasters or by human activity. If the ecosystem has a limited variety of species, then destroying even one species of plant or animal can change the ecosystem forever. A resilient ecosystem, however, is able to restore itself to its original, pre-disturbance condition. Resilience in an ecosystem is possible when the ecosystem is populated by a large variety of species: if one species is eliminated by a disturbance, other species are able to take the place of that species, which allows the ecosystem to avoid long-term change.
听力材料：
OK, this happened a few years back. There was this healthy coral reef in the Pacific Ocean—you know how gorgeous coral reefs are, with all the red, pink, and orange—and it had a huge variety of species... um, of fish and plants... that it protected and provided with food. Then the seawater got polluted, because a ship spilled a large amount of diesel fuel. The pollution caused a species of fish to die out.
And this fish that died out used to eat a particular type of ocean plant called algae. Now... of course... if there aren’t any fish to eat algae, the algae will grow out of control and there’ll be too much algae, which is very bad for coral. But that did not happen to this coral reef—know why it didn’t happen?
Because there were still many other species left that ate that same algae. So even though the algae increased at first, so did the population of the other fish species who ate the algae, because there was more algae for them to eat. The other species took over for the fish that died out, and eventually, the coral reef looked about the same as before.
Now think about what would have happened to this coral reef if there had not been a wide variety of different fish species. If that one species of fish that ate algae had died off—well, you can imagine—soon the whole coral reef would have been covered in algae.
Question：
Using the coral reef as an example, explain what it means for an ecosystem to be resilient.
