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TPO 6 Lecture 2
Biology
Narrator
Listen to part of a lecture in a biology class.
Professor
Ok, I have an interesting plant species to discuss with you today. Uh…it’s a species of a very rare tree that grows in Australia, Eidothea hardeniana, but it’s better known as the Nightcap Oak.
Now, it was discovered only very recently, just a few years ago. Um… it remained hidden for so long because it’s so rare. There are only about 200 of them in existence. They grow in a rain forest, in a mountain rage…range in the north part of New South Wales which is uh… a state in Australia. So just 200 individual trees in all.
Now another interesting thing about the Nightcap Oak is that it is…it represents…uh…a very old type…uh…kind of tree that grew a hundred million years ago. Um, we found fossils that old that bear remarkable resemblance to the tree. So, it’s a primitive tree. A…a living fossil you might say. It’s relic from earlier times and it has survived all these years without much change. And it…it’s probably a kind of tree from which other trees that grow in Australia today evolved.
Just to give you an idea of what we are talking about. Here’s a picture of the leaves of the tree and its flowers. I don’t know how well you can see the flowers. They’re those little clusters sitting at the base of the leaves.
Okay, what have we tried to find out about the tree since we’ve discovered it? Hmm…or how…why is…is it so rare?It’s one of the first questions. Um… how is it…um…how does it reproduce? It’s another question. Um, maybe those two questions are actually related. Jim?
Student
Hmm …I don’t know. But I can imagine that…for instance, seed dispersal might be a factor. I mean if the…er…you know, if the seeds cannot really disperse in the wild area, then, you know, the tree may not colonize new areas. It can’t spread from the area where it’s growing.
Professor
Right. That’s…that’s actually a very good answer. Uh, of course, you might think there might not be many areas where the tree could spread into, er…because…um…well, it’s very specialized in terms of the habitat. But, that’s not really the case here. Um…the suitable habitat, that is, the actual rainforest is much larger than the few hectares where the Nightcap Oak grows.
Now this tree is a flowering tree as I showed you. Um…um…it produces a fruit, much like a plum. On the inci…inside there’s a seed with a hard shell. It…it appears that the shell has to crack open or break down somewhat to allow the seed to soak up water. You know, if the Nightcap Oak remains…if their seeds remain locked inside their shell, they will not germinate. Actually, the seeds…er…they don’t retain the power to germinate for very long, maybe two years. So there’s actually quite a short window of opportunity for the seed to germinate. So the shell somehow has to be broken down before this…um…germination ability expires. And…and then there’s a kind of rat that likes to feed on the seeds as well. So, given all these limitations, not many seeds that the tree produces will actually germinate. So this is a possible explanation for why the tree does not spread. It doesn’t necessarily explain how it became so rare, but it explains why it doesn’t increase.
OK, so it seems to be the case that the species, this Nightcap Oak is not very good at spreading. However, it seems, though we can’t be sure, that it’s very good at persisting as a population. Um…we…there’s some indications to suggest that the population of the Nightcap Oak has not declined over the last. er…you know, many hundreds of years. So it’s stayed quite stable. It’s not a remnant of some huge population that is dwindled in the last few hundred years for some reason. It’s not necessarily a species in retreat. Ok, so it cannot spread very well, but it’s good at maintaining itself. It’s rare, but it’s not disappearing.
Ok, the next thing we might want to ask about a plant like that is what chances does it have to survive into the future. Let’s look at that.
《生物学》
独白：听一段生物课上的录音。
教授：今天我们将要讨论一种奇特的罕有的植物品种：Eidothea hardeniana 树，它生长于澳洲，也被称为夜冠橡树。夜冠橡树因其罕见而隐藏了很久，直到近几年才为人们发现，目前存活个体仅有200株，它们生长在澳大利亚新南威尔士州北部山脉的热带雨林区。夜冠橡树的奇特之处在于，它属于某种存活于一亿多年前的古老树种，并与迄今发现的古老化石具有惊人的相似之处。因此可以说，夜冠橡树是原始植株，也是活化石，它是历经亿年风雨存活至今的遗迹，人们甚至可以推断，当今澳洲生长的诸多树种都是由夜冠橡树进化而来的。以上是关于夜冠橡树的简介，下面请同学们观看一张夜冠橡树树叶和花朵的照片。我不知道大家是否能看清楚，那些位于树叶底部的小花簇就是其花朵。夜冠橡树究竟有哪些谜题值得我们去探索呢？首先，为何它如此稀少？另外，夜冠橡树是如何繁殖的呢？也许这两个问题是紧密联系的。Jim你来谈谈？
学生：嗯，我不确定，种子的散播或许是影响橡树繁殖的重要因素。如果夜冠橡树的种子无法在广阔区域内散播、生长，那麽树种就无法拓展新领域，因此其繁殖也就无法突破原生地的地理范围。
教授：回答得很好。同学们或许认为夜冠橡树能够生存的区域很稀有，即它对生长环境的要求很独特，(因此繁殖受到了限制)。但事实并非如此：适合夜冠橡树生长的热带雨林区面积广阔，远远超过其现今存活的几公顷范围。(所以，种子散播并非导致夜冠橡树极为罕有的原因。)请同学们思考一下，夜冠橡树是开花植株，能够结出梅子状果实，其种子外包有坚硬的外壳。只有在外壳被击破或打碎的情况下，种子才能接触到水分；一旦种子被封闭在外壳内，那麽发芽生长就无法实现。事实上，种子的发芽能力只能持续两年左右，因此夜冠橡树的种子必须在此段时间内突破外壁，(否则就将死亡)。另外，当地某种鼠类喜欢以橡树种子为食，(这也对夜冠橡树的繁殖造成了威胁)。
因此，由于以上原因，仅有少数夜冠橡树种子能够成功地发芽生长，这虽然不能解释夜冠橡树为何如此稀少，但或许可以说明为什么夜冠橡树繁殖如此有限，以至于数量无法激增。综上所述，夜冠橡树似乎并不是善于扩展领地积极繁殖的物种，但它的确是生命力极强的物种。部分证据显示，夜冠橡树的数量在过去的数百年内都未发生明显减少，其个体数量极为稳定。因此，现存的200株夜冠橡树并非数百年前丰盛繁殖的剩余，它也并不处于物种衰退期。可以说，夜冠橡树繁殖力不强，但生命力强，它虽然稀少却并不面临灭绝的危险。那麽接下来我们将要讨论，夜冠橡树一类的植物种群在未来得以存活的几率有多大，让我们继续分析。
以上就是托福听力TPO6原文中Lecture 2的文本内容，希望大家能够用心体会，更多TPO文本内容小编稍后为您呈现。最后，小编祝大家在托福考试中取得好成绩！
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