FIGURE 20.6 Mutualism. Acacia trees and Pseudomyrmex ants have each evolved adaptations that enhance their mutualistic interaction. The trees’ thorns serve as nest sites for the ants (inset) and provide them with food in the form of nectar produced in specialized nectaries (arrow). In return, the ants protect the trees from herbivores and competing plants.
(Oxford Scientific/Getty Images; inset: Alex Wild Photography)