（每日一读）2014年高考英语8月考前突破 阅读理解能力 文化教育 偷猎死亡的非洲大象数量达到临界值素材

偷猎死亡的非洲大象数量达到临界值Africa's elephants have reached a tipping point: more are being killed each year than are being born, a study suggests.研究显示，非洲大象的数量已达临界值：每年被猎杀的大象比出生的大象都要多。 Researchers believe that since 2010 an average of nearly 35,000 elephants have been killed annually on the continent. They warn that if the rate of poaching continues, the animals could be wiped out in 100 years. The work is published in the Proceedings of the National Academy of Sciences. Lead author George Wittemyer, from Colorado State University, said: "We are shredding the fabric of elephant society and exterminating populations across the continent."Dramatic loss The illegal trade in elephant tusks has soared in recent years, and a kilogram of ivory is now worth thousands of dollars. Much of the demand has been driven by a rapidly growing market in Asia. While conservationists have long said the outlook was bleak, this study provides a detailed assessment of the impact this is having on Africa's elephants. The researchers have found that between 2010 and 2013, Africa lost an average of 7% of its entire elephant population each year. Because elephant births boost the population by about 5% annually, this means that overall more of the animals are being killed than are being born. Julian Blanc, who also worked on the study, from the Convention on International Trade in Endangered Species of Wild Fauna and Flora (Cites), said: "If this is sustained, then we will see significant declines over time. "The other thing to bear in mind is that different areas are affected differently. "There are still healthy growing populations in parts of Africa, Botswana for example. But in other places the poaching levels are devastatingly high, and that is particularly the case in Central Africa." In Central Africa it is estimated that elephant numbers have fallen by about 60% in a decade.