Plants offer two basic types of rewards for the services of ants: housing and food. Housing was discussed in Chapters 2 and 3 and will not be taken up at length here. Food, or nutrition, will be treated in a broad sense. Thus, in addition to carbohydrates, proteins, and lipids ingested for normal metabolism, development, and growth, substances necessary for social organization such as those required for the biosynthesis of mating pheromones, alarm, and defense will be included. Also it should be borne in mind that substances that attract ants to a reward are not necessarily those from which they derive the primary benefit. That is, the distinction between attractants and nutrients may be crucial (Marshall, Beattie, & Bollenbacher 1979).

Ant nutrition

Most ant species involved in seed dispersal or plant protection are omnivores, and the plant rewards harvested by them while performing these services are only part of their overall nutrition. Individual colonies may opportunistically exploit extrafloral nectar, or elaiosomes on seeds at an intensive level for short periods; but almost invariably some workers are foraging at other resources at the same time. A major consequence of this is that the intensity with which plant rewards are harvested varies enormously.

This scenario is not at all surprising when it is remembered that the nutritional requirements of ants vary with the state of the colony, and conversely, the food available to a colony influences the number of individuals or castes.