This study tests the hypothesis that the percentage of tree and shrub species within categories of seed dispersal, fruit size and type is directly related to rainfall in the caatinga vegetation, a tropical dry forest of the north-eastern Brazil. The percentage of vertebrate-dispersed species ranged from 11% in a 246-mm year−1 plot to 53·6% in a 663-mm year−1 plot. In addition, the percentage of berry species was positively correlated with annual rainfall, whereas the percentage of drupe species was negatively correlated. Among the group of vertebrate-dispersed species, a significant increase was found in the percentage of Myrtaceae species (0–16·7%) from dry to moist plots. Our results support trends described in the literature reporting gradual and predictable changes in seed dispersal mode in neotropical forests located across rainfall gradients.