ECOLOGY OF FORAGING *4060 BY ANTS

Ants (Formicidae)2 have received much attention by taxonomists, ethologists, and biochemists (10, 16, 20, 133, 134, 175). Little attention has been given to the ecology of their food gathering, a major selective force in the evolution of their morphology, ethology, and biochemistry. In this review we wish to collate and reinterpret some of the widely scattered observations on ant foraging ecology. First and foremost, we must recognize that selection in this system is not operating at the level of the individual ant; as Wilson (174) has so properly emphasized, colony fitness is the only near approximation we have of worker ant foraging "success." Second, ant colonies forage primarily for particulate and widely scattered food items. Sugar-rich exudate from extra-floral nectaries and their homopteran animal counterparts is the only stationary and immediately renewable food harvested by many species of ants. Third, most ant species are scavengers on animal matter. In addition, they range from active predators to seed gatherers, including extreme generalists such as swarm-raiding army ants (Ecitoninae, Dorylinae) to specialists on termites (Megaponera and Termitopone), centipedes (Amblypone), and other ants (Cerapachyinae). A few are even obligatory foragers on the vegetative parts of specific plants (Attini, Azteca, Pseudomyrmex, Pachysima). In Table 1 we list food characteristics of major importance in selection for colony and worker foraging patterns. None of these characteristics is likely to dominate the entire foraging ecology of an ant species because the characteristics are not mutually exclusive and because ants harvest food types that require mixed foraging strategies in space and seasonal time. For example, desert seed-harvesting ants obtain large