许昌济源平顶山2020年高三第二次质量检测文综答案及试题（高三文科综合）。This is not the first time researchers have observed a great change in the population of elephants. At Zambia's South Luangwa National Park and Lupande Game Management Area, areas which were heavily hunted in the 1970s and 1980s, 35% of elephants 25 years old or older and 13%of those younger than 25 are now without tusks. A 2008 study published in the African Journal of Ecology found that the number of tuskless females at the Ruaha National Park in Tanzania went from 10.5 percent in 1969 to almost 40 percent in 1989, largely due to illegal hunting for ivory.