PTE Retell Lecture真实讲座练习:黄石公园里的山杨丛

在PTE中,无论是Summarise Spoken Text 还是 Re-tell Lecture的考题大都是从真实的讲座或者演讲中截取的,中间经常经常夹杂很多不同的环境音.很多同学都反映有时未必是听不懂,而是听不到. 鉴于此,墨尔本文波雅思PTE专门为大家总结了真实讲座的PTE练习音频,相比新闻音频来说,整体更加接近PTE考试的真题,内容方面,我们也会为大家提供考试中存在的近似题,最近我们会持续更新,敬请期待!





So what’s happened in Yellowstone over the last 20 years since the reintroduction of the wolf. Well, the wolf population has oscillated a bit, you know, causes seasonal changes in good years, bad years etc, but there’s been a pretty steady decline in elk numbers across the range. Perhaps may be a sixty to seventy percent decline in elk numbers and that was predicted by a biologist, put a pack-hunting carnivore that likes elk especially young elk and that’s going to debt elk   numbers over time. What else has happened.If you look at what’s been going on on trees in the system and you measure the degree of browsing, the trees browsing is noticeably declined, the height of aspen is noticeably increased. So the suppression of elk populations do in significant part to the reintroduction of wolves is having an effect on the vegetation and in fact more effects than anyone predicted, because if you look at other populations of trees things like willows. Here is a picture taken before wolf reintroduction and this is in the foreground this is will that grow alongs stream banks and Yellowstone if it’s heavily browsed, but after wolf reintroduction they see that all this willow starts growing back along the stream banks. Same with cottonwood trees. And it turns out that willow is both a favourite food and building material for beavers and once the beavers get in there they start sort of changing the course of the river building dams things like this. And it turns out in the 20 years since wolf reintroduction you see an increase in the number of beaver colonies in the Yellowstone system. So introducing a carnivore has affected the herbivore, the elk, it’s affected the trees like Aspen, willow, cottonwood but in turn there’s a cascading effect on other creatures like beavers, even other predators like coyotes and foxes and things like that. So reintroducing the wolf introduced one of these cascades and introduce the rebound of trees and other species and Yellowstone.


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