托福TPO20 Lecture4

TPO20 Lecture4-Biology(Snowshoe Hare) Narrator Listen to part of a lecture in a biology class. Professor Now, James, you said you had been to the State of Maine, right? Student Yeah, actually I lived in western Maine until I was about sixteen. Professor Great. So why don’t you tell everybody what is like there in the winter? Student The winter? Well, it’s cold. And there’s lots of snow, you wouldn’t believe how much snow we used to get. Professor Actually I would. I did field research up there a couple of winters. And it really is an incredible environment. And to survive in that sort of environment, animals have to adapt, to evolve in response to their surroundings. As you recall, an adaptation is any feature, um... physical or behavioral feature of a species that helps it survive and reproduce. And in adapting to extreme climates, like Maine in the winter time, animals can evolve in pretty interesting ways. Take, for example, the snowshoe hare. Ok, the snowshoe hare, and of course, that’s H-A-R-E, like a rabbit. Although I probably should mention that technically a hare is not exactly the same as a rabbit, even though it is very similar . The primary difference is that a rabbit’s young are born blind and without fur , while a hare’s babies are born with a full coat and able to see. Now, the snowshoe hare, tell me, what sort of adaptations do you think it has developed that help it survive the Maine winters? I’ll give you a hint. Food isn’t an issue. The hare actually has abundant food in the small twigs it finds. Student Well, I don’t know. I mean, I know we used to try to look for these rabbits, eh... hares, when we went hiking in the winter , but it was often hard to find them in the snow. Professor Yes. That’s exactly right. The major concern of the snowshoe hare in the winter is predators. And now that includes humans. So one of its adaptations is basically camouflage. In other words, its coat, its fur , turns from brown in the summer to white in the winter , which makes it harder for the hare’s predators to see it against the white snow. Student Yeah, but I could swear I remembered seeing rabbits in the snow a couple of times, I means hares, that were brown. Professor Well, you may very well have. Timing is really important, but the snowshoe hare doesn’t always get it exactly right. Its chances for survival are best if it turns white about the time of the first snowfall. And it’s the amount of daylight that triggers the changing of the hare’s coat. As the days get shorter , that is, as the Sun is up for a shorter and shorter time each day, the snowshoe hare starts growing white fur and shedding its brown fur . The hare does a pretty good job with its timing, but sometimes when there’s a really early or late snow, it stands out. Plus, it takes about a month for the snowshoe hare’s coat to completely change color . So if there’s a particularly early snowfall, it’s very likely that the hare’s fur would not yet be totally white. And that would make this a particularly dangerous time for the hare. OK. What else? Other adaptations? Susan? Student Well, it’s called the snowshoe hare, so are its feet somehow protect it from the cold? Professor Well, this animal’s name does have to do with an adaptation of its feet. Uh... though, not like it has warm furry boots or something to keep its feet from getting cold. You’ve probably never needed to wear snowshoes. But, well, snowshoes are not like thick furry shoes designed to keep the feet warm, they are actually quite thin, but very wide. What they do is spread out the weight of the foot coming down on the snow. See, the problem with walking on snow is that you sink in with every step. But with snowshoes, you don’t sink in, you walk on top of the snow. It makes walking through the Maine countryside in the winter much easier . Anyway, the snowshoe hare has an adaptation that plays on the same idea. It has hind feet that act like snowshoes. I mean, it’s paws are wide and they allow the hare to hop and run just at the surface of deep snow. And this is a huge advantage for the snowshoe hare since by contrast, the feet of its predators usually sink right down into the snow. Now, another advantage related to this is that unlike many animals in winter, snowshoe hares can stay lean and light weight. They accumulate essentially no body fat. Can anyone guess why this is so? Student They don’t eat very much? Professor Well, yes. But not because there isn’t enough food around. It’s because, like I said, food is almost always within reach, and they don’t have to store up a lot of food energy for the harsh winters.