Temporal consistency in interactions among birds, ants, and plants in a neotropical savanna

Interactions among animals and plants are key to understanding seed
dispersal, plant regeneration and plant community patterns. These
interactions can be dynamic, with changes of species and functional roles
across space and time. Despite fluctuations in species abundances and
resources over time being the rule in natural communities, most studies
approach plant-frugivore interactions as temporally static. We documented
changes in bird and ant species in interactions with plants producing
carbohydrate- (Miconia rubiginosa) or lipid-rich diaspores (Xylopia
aromatica) comparing two fruiting seasons 15 years apart in a savanna in
southeastern Brazil. We tested if abundance and body size of dispersal
vectors (birds and ants) affected the frequency of interactions and the
quantitative effectiveness of seed dispersal (QTC). Rich bird (26 species)
and ant (18 genera) assemblages interacted with the diaspores. A core of
bird and ant taxa was temporally consistent, and responsible for most seed
removal across the two years for both plants. Temporal transience was more
common for sporadic partners of interactions, and for species with similar
functional roles. Abundance and body size of birds affected the
interspecific contributions to QTC. Large-bodied birds dispersed large
quantities of seeds of our relatively small-seeded plants, even if their
visits were sporadic. For ants, variations in temperature and rainfall
across time seems more important in driving variations in the
contributions to QTC. The combined effect of birds and ants in the same
system help to stabilize the temporal fluctuations in the amount of seeds
dispersed. However, ants alone are unlikely to replace the functional
roles of vertebrate dispersers. Even though species in the assemblage
change either their quantitative contribution to seed dispersal or their
presence or absence in the interaction network, species persisting in
interaction over time are the most important quantitative partners for
plants.