The ants protect the tree from predators, and, also, from other plants or trees vying for sunlight. The tree in turn provides food and shelter (thorns) for the ants. When an insect tries to eat from the tree, the ants attack the insect. If a vine tries to climb the tree to get sunlight, the ants chew off the vine. Also, the ants eat any seedlings growing at the base of the tree.
If an Elephant tries to eat from the tree, the ants start swarming up the insides of their trunks. Then they did a study in Africa. They put fences around a few trees to protect them from predators. After only a few short years, the trees started to look kind of ragged and their growing rates slowed down.
Turns out the trees no longer needed the ants. So… they produced much less nectar and smaller and fewer thorns for the ants to live in. The ants abandoned the trees, and insects started attacking the trees. Researchers are now going to remove the fences to see if the ants will return after large animals begin to eat from the trees.
As interesting as that is, I find this next fact even more interesting: When it is time for the Acacia tree to get pollinated by insects, the tree sends out a chemical that drives the ants away from the tree. After the tree has been pollinated, it stops sending out the chemical and the ants return. And the media and Evolutionists want us to believe all this happened by random chance and with no intelligent design involved?