英語時(shí)差:金合歡樹，螞蟻和大象

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Acacias, Ants And Elephants D:Hey,Yael, what ants, acacia trees and elephants have in common? Y:Hmm,I don't know,Don. D:Ants, acacia trees and elephants are linked together in a somewhat ironic relationship. Acacias are thorny scrubby African trees.Acacia leaves are an important food source for many of Africa’s largest herbivores such as giraffes, zebras and elephants.Such large grazers can do significant damage to an acacia tree. In order to deter these hungry browsers, the whistling acacia has formed an alliance with ants. The acacia trees provide housing and sugary nectar for the ants.And in return armies of these biting ants swarm any animals attempting to eat the trees.It turns out that although the trees invest a lot of resources in the protective ants, trees that are grazed by big animals actually survive better than trees that aren’t grazed at all. Y:Surprising！Why it that? D:When the trees are munched by large herbivores they develop special hollow thorns the protector ants like to live in, and produce a sweet nectar for the guard ants to eat. Fenced off trees, while protected from hungry giraffes and elephants, stop producing homes and nectar for the ants.The disappearance of the protector ants allows a different species of ant to move in and take over. These new ants promote the activity of destructive stem boring beetles, which can stunt the growth and even kill acacia trees. Y:I see.If not for the damage from hungry elephants, the tree doesn’t invest energy to house and feed the ants. But without its relationship with the protector ants, the tree suffers even more.

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