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  3. Wild elephants roam across the crowded plains of India; forested river banks wind through cattle ranches in Brazil; a ribbon of

Wild elephants roam across the crowded plains of India; forested river banks wind through cattle ranches in Brazil; a ribbon of

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问题     Wild elephants roam across the crowded plains of India; forested river banks wind through cattle ranches in Brazil; a ribbon of green stretches across Europe where the Iron Curtain used to be. Using such wildlife corridors to link up larger but isolated protected areas are the most widely adopted strategy for halting biodiversity decline, with millions of dollars spent creating and protecting them every year. But has enthusiasm for a neat idea got ahead of the science?
    The principle is simple. As wildlife habitat is broken into isolated fragments by farms, roads, and settlements, we need to link them up with corridors of green. Then even if the entire habitat cannot be re-created, old migration patterns can be revived, escape routes created ahead of climate change and—perhaps most crucially—isolated populations can interbreed, enhancing their genetic diversity and their resilience to encroaching threats.
    Recently, Paul Beier, a veteran conservation biologist from Northern Arizona University, and his colleague Andrew Gregory, warned that "despite much research, there is little evidence that conservation corridors work as intended. " There is, they say, plenty of evidence that wild animals will move through corridors. But advocates of the corridors want, and claim, much more than this. They say that animals don’t just go for a walk in their conservation woods, but that they move permanently and interbreed with neighboring populations. In this way corridors supposedly unite isolated, threatened populations into an interbreeding and much more resilient—whole.
    Such claims sometimes hold up. In the United Kingdom, the expansion of Kielder Forest in the 1960s provided a link between isolated populations of threatened red squirrel. Genes from isolated populations have now "leapfrogged through hundreds of forest fragments" across 100 kilometers and more. But the Kielder Forest is much wider than a conventional corridor. Few studies have looked for gene flow in genuine corridors; even fewer have found it. One study investigated the genetic diversity of small marsupials in a narrow forest corridor traversing 4. 5 kilometers of grasslands in Queensland, Australia. It found that genetically distinct populations had persisted at either end. Mixing was a myth.
    Other studies have shown that conservation corridors work. But most have looked at short corridors of 100 meters through largely natural landscape. "That species can travel a-long short corridors in a natural setting does not mean that they will be successful dispersing along much longer corridors embedded in a heavily impacted landscape," says Gregory. "Still less that such movements occur frequently enough to allow enough gene flow to occur so that the connected habitat blocks function as one population. "
    Perhaps we should not make the perfect the enemy of the good. Surely any corridor is better than none? But consider this. The edges of wild areas are known danger zones for wildlife, where predators and diseases may invade. Linking two existing protected areas with a long narrow corridor may expose it to greater danger along these edges. Unless the benefit exceeds the threat, then there is serious potential to do harm.
According to paragraph 4 and 5, corridors supposed to be effective are______.
选项 A、wide and set in natural landscape
B、narrow and set in impacted landscape
C、long and set in natural landscape
D、short and set in impacted landscape
答案A
解析 比较题需要综合考虑四个选项中所涉及的各个因素。
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