2015개정 영어 천재(이) 5과 본문

영어 천재이 5과 본문.hwp

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5과 – Keystones in Nature

 

Host: Welcome to Student Science Show. Today, we'll be discussing an important topic―keystone species, and our special guest is an expert on ecosystems and the environment. Dr. Walters, welcome!

Dr. Walters: It's my pleasure to be here.

Host: Dr. Walters, let's get right to the point. What exactly is a keystone species?

Dr. Walters: Well, it's one species that has a huge effect on the ecosystem where it lives.

Host: What do you mean?

Dr. Walters: Well, have you ever noticed the keystone on a stone arch? It's only one stone of many, but without it, the whole arch would fall.

Host: The keystone makes the whole arch stay strong even though it's only one small stone?

Dr. Walters: It's the same in an ecosystem. An animal might not be the biggest in size or number, but without it, the ecosystem would collapse.

Host: Oh, you mean that sometimes one stone, or one species, can be especially important?

Dr. Walters: Exactly.

Host: Is this a new term?

 

Dr. Walters: Actually, the term "keystone species" was first used by Dr. Robert Paine, a zoology professor, in 1969. He examined food chains on Tatoosh Island in the U.S. state of Washington. He observed that diversity decreased during periods when the number of predators decreased. In other words, when fewer predators hunted in the system, there were fewer other living things in the ecosystem, too.

Host: Did he focus on one particular species?

Dr. Walters: Yes, he saw that purple sea stars were very important because they hunt mussels on Tatoosh Island. When the sea stars were removed, the number of mussels increased greatly. The mussels took over the area and left little room for other species. When the sea stars were present, however, the ecosystem where they lived remained properly balanced. Many species could live well together. This is why he called purple sea stars a "keystone species."

Host: So, a keystone animal eats other animals, right?

Dr. Walters: Yes, but not always. Not just meat-eating animals but also plant-eating animals can be keystone species. Elephants, for instance, play this role in the Serengeti plains of Tanzania. Elephants eat small trees on the plains. Because they're able to knock over the trees and pull the roots out, elephants prevent the trees from growing big and taking over the area.

 

Host: Well, Dr. Walters, I don't get it. How does removing the trees help the ecosystem?

Dr. Walters: OK, here's what removing the trees does. It helps the grass grow freely and become food for animals such as antelopes and zebras. Smaller animals such as mice can also make their homes in the dry soil warmed by sunlight. In turn, predators such as lions and hyenas depend on all these animals for food. The ecosystem is balanced and able to maintain many species. In this situation, the elephants are the keystone species because without them, the ecosystem would change.

Host: Are there keystone species all around the world?

Dr. Walters: The term was first used in the U.S., and the elephants I mentioned live in Africa. But these species are everywhere. For instance, in Europe, rabbits are a keystone species.

Host: Rabbits?

Dr. Walters: Yes, scientists have discovered that the European rabbit is a very important species in southern Europe.

Host: How so?

Dr. Walters: They keep the ecosystem balanced in many ways. First, they affect it by eating plants and spreading their seeds. This not only creates open spaces but also helps maintain plant diversity.

 

Host: Do the rabbits also eat other animals to help maintain balance?

Dr. Walters: Actually, in this case, it's the opposite. Many other animals in the system hunt the rabbits for food. In other words, rabbits help many other animal species survive.

Host: Then, is there anything people can do to protect keystone species?

Dr. Walters: Yes, there are many things, but the most important one is to avoid hunting them or disturbing the ecosystem significantly. Many elephants in Tanzania, for example, have disappeared because people have hunted them. We must also do much more research. This is as important as not hunting. We must identify the animals and plants that are keystone species so that we can better preserve them in the future.

Host: Doing that work sounds very interesting and rewarding.

Dr. Walters: Yes, but it's not easy, and I think this poses a great challenge for today's teens.

Host: I'm sure you've been a great inspiration to our listeners. Thank you for being on our show, Dr. Walters.

Dr. Walters: You're welcome. And feel free to email me with more questions!

 

 

Further Reading

Interesting Facts About Whales

Whales, the largest animals on earth, swim to the deepest parts of the sea to feed and come up to the surface to breathe. While they are near the surface, they release waste from their body. This way, they bring essential nutrients from the deep sea to the surface waters. These nutrients form the base of all marine food chains and keep the marine ecosystem running.

Whales are also really important after they die. The dead body, also called "whale fall," sinks toward the bottom of the sea and becomes food for many fish species that live in the harsh conditions of the sea floor. In addition, the dead body is good for the environment. As it has a lot of carbon in it, by sinking to the sea floor, it keeps the carbon out of the atmosphere. According to marine scientists, the amount of carbon that whales take to the bottom of the sea is about 190,000 tons annually, which equals the amount of carbon produced by 80,000 cars.