Ants associated with acacias remove competing vegetation, attack herbivores, and patrol the host, while the plant supplies nesting space in hollow thorns and food through extrafloral nectar or nutrient-rich food bodies. Removing neighboring plants reduces competition for light, water, and soil nutrients, thereby increasing acacia growth and survival. The ants gain reliable resources and shelter, so both participants receive a net fitness benefit and the interaction is mutualistic. Its prominent service is defensive because ant activity protects the plant from herbivores and competitors, although resource exchange supports that service. Predation would describe ants consuming another organism without a reciprocal benefit from that victim, while amensalism would assign no benefit to the ants. Parasitism would require ant benefit at a net cost to the acacia. Outcomes can vary: poorly protective ants may exploit plant rewards, and excessive ant activity may impose costs. In well-studied obligate acacia–ant systems, however, reciprocal benefits and partner-specific adaptations demonstrate coevolved mutualism rather than a one-sided interaction.
Ref:
Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 8-13
