Walk through the vegetation almost anywhere on earth and you will see ants foraging on plants. The basic interaction has evolved into four ant–plant mutualisms in which ants: (1) protect plants from herbivores and other enemies, (2) feed plants essential nutrients, (3) disperse seeds and fruits, and (4) pollinate. Rewards produced by the plants, chiefly nest sites or food, are utilized by ants and the behavior patterns involved result in one or more of these services.

Much more is known about the benefits to the plants than the benefits to the ants. For example, the anatomy and morphology or chemistry of many of the rewards borne by the plants have been described. Critical field experiments have been performed to test the impact of ant services on plant growth, survivorship, and fecundity, and it is clear that ant services can profoundly affect plant fitness. On the other hand, although ants eagerly occupy plant-borne nest sites and harvest plant-borne food rewards, almost nothing precise is known about how this affects ant fitness. A major gap in our knowledge of ant–plant mutualisms is how the food rewards affect the physiology, growth, and demography of ant colonies. As a consequence of this situation, this book is written primarily from a “plant's point of view.” It also should be noted that fundamentally nonmutualistic ant–plant interactions, such as predation by seed-gathering ants and herbivory by leaf-cutter ants, are referred to only in passing.