阅读理解Have you ever wondered how many ants there are on the earth? Scientists at the University of Hong Kong certainly have. In a new study, they estimated (估计) the number of the world's ants is about 20, 000, 000, 000, 000, 000(20 with 15 zeroes!
That means for every human, there are nearly 2. 5 million ants. If you put all the ants on a scale, they'd weigh more than all the wild birds and mammals (哺乳动物) on the earth.
How did they count such a big number? In the past, many scientists have counted ants in different areas. They collected fallen leaves and earth and dried them to force the ants to come out for counting. Based on 465 studies that cover the whole land, the new study made the estimation. According to Wang Runxi, one of the authors, the number and distribution(分布) of ants can be valuable to show the environmental changes.
"Ants play an important role in the ecosystem, " Wang told Science and Technology Daily. "They help loosen the soil, spread seeds, break down things and form a part of the food chain (食物链). They are everywhere on the earth except for the coldest places. "
"Compared with big animals, little ants are more sensitive (敏 感 的 ) to environmental changes, " Wang added. Most ants live in tropical (热带的) and subtropical(亚热带的) areas. But in recent years, ants have been moving toward the two poles because of global warming. Changes in forests, such as too many trees being cut down, also have influence on the number of ants, the study showed.
"Our global map of ants allows us to better understand and predict ants' responses to worrying environmental changes, " scientists wrote in the study.
