Figure 17.7 A mutualism between ants and acacia trees. (a) Acacia trees, such as this swollen thorn acacia in Panama, have large brown thorns that the ants can hollow out for nests where they can raise their larvae. The plants also have green nectaries that provide nectar the ants consume. In exchange for these benefits, the ants attack herbivores that try to eat the acacia tree and they attack vines and other plants that grow near the acacia tree. (b) Because the ants attack encroaching plants, acacia trees with ants are typically surrounded by bare ground.

Photos by Alexander Wild.