Ant-plant mutualisms are ubiquitous in tropical forests and are ideal systems for examining ant competition, multi-trophic interactions and plant defensive strategies. I studied the patterns of ant habitation and insect herbivory of Cordia alliodora (Ruiz and Pavon) Oken trees in relation to plant age and fertilization treatment. Plant age clearly influenced patterns of ant occupancy of C. alliodora, with either Azteca pittieri Forel (Hymenoptera: Formicidae) or Crematogaster carinata Mayr (Hymenoptera: Formicidae) occupying the majority of domatia by the time trees reached maturity. Habitat heterogeneity and competition between A. pittieri and C. carinata facilitated the coexistence of several other ant species on trees inhabited by these two numerically dominant taxa. Herbivory on 1yr old trees was affected by fertilization treatment and plot, suggesting that during this stage plants are protected primarily by chemical anti-herbivore defenses. By contrast, herbivory on 5yr old trees was only significantly affected by ant occupation, with the presence of both A. pittieri and C. carinata reducing herbivory as a function of the number of patrolling workers. However, a laboratory feeding trial with the main insect herbivore at the site, Coptocycla leprosa Boheman (Coleoptera: Chrysomelidae) largely corroborated the results of the natural herbivory survey, demonstrating that neither ants nor phytochemicals completely deter this specialist herbivore. These results suggest the evolution of a growth-defense tradeoff over ontogenetic stages in which plants shift allocation of resources from chemical defenses toward the production of nodes that allows larger colonies of mutualist ants to inhabit the plant.