Ant–plant mutualisms are useful models for investigating how plant traits mediate interspecific interactions. As plant‐derived resources are essential components of ant diets, plants that offer more nutritious food to ants should be better defended in return, as a result of more aggressive behavior toward natural enemies. We tested this hypothesis in a field experiment by adding artificial nectaries to individuals of the species Vochysia elliptica (Vochysiaceae). Ants were offered one of four liquid foods of different nutritional quality: amino acids, sugar, sugar + amino acids, and water (control). We used live termites (Nasutitermes coxipoensis) as herbivore competitors and observed ant behavior toward them. In 88 hr of observations, we recorded 1,009 interactions with artificial nectaries involving 1,923 individual ants of 26 species. We recorded 381 encounters between ants and termites, of which 38% led to attack. Sixty‐one percent of these attacks led to termite exclusion from the plants. Recruitment and patrolling were highest when ants fed upon nectaries providing sugar + amino acids, the most nutritious food. This increase in recruitment and patrolling led to higher encounter rates between ants and termites, more frequent attacks, and faster and more complete termite removal. Our results are consistent with the hypothesis that plant biotic defense is mediated by resource quality. We highlight the importance of qualitative differences in nectar composition for the outcome of ant–plant interactions. Abstract in Portuguese is available with online material.

Ants are diverse and ecologically important organisms in tropical forests, where their spatiotemporal distribution can be highly complex. This complexity arises mainly from marked differences in microclimatic conditions and resource availability through space and time that is even more evident in highly seasonal environments, such as tropical dry forests. However, it is unclear how seasonality interacts with other factors that might shape temporal variation of ant composition (β-diversity), like vertical strata and habitat disturbance. Our goal was to examine the potential influence of vertical stratification and the successional stage on the spatiotemporal variation of a tropical dry forest's ant species composition. We assessed whether species turnover or nestedness was the main component determining the spatiotemporal β-diversity of ant communities across the canopy and litter strata. We sampled canopy and litter ants in ten plots, half in the early and half on the late stage of secondary succession at four times, twice in wet and twice in dry season. A high species turnover defined the spatiotemporal β-diversity of canopy and litter ant communities across years and seasons in our focal dry forests. Importantly, the temporal ant species composition was much more stable in the canopy than in the litter. Moreover, we found that the ant community's temporal dynamics was consistently high across successional stages, not differing in the temporal β-diversity between early and late succession. Our results provide valuable insights into the potential underlying causes of community assembly and spatiotemporal dynamics in seasonal habitats, like the highly threatened and diverse tropical dry forests.