In regions with strongly seasonal climate, plant phenological strategies are highly constrained by abiotic factors. In contrast, plants growing in continually wet, tropical forests are freed from most abiotic constraints, and phenological patterns should be subject to selection from mutualists (pollinators and seed dispersers) and antagonists (seed predators and pathogens). Yet the extent to which species interactions influence the reproduction of tropical plants is poorly understood. We studied the phenology and fruiting ecology of fifteen species of bird-dispersed understory trees at three elevations on the Atlantic slope of Costa Rica. Sites were within the wettest forests of Central America and had similar seasonality in climate, but differed in the amount of rainfall, elevations, temperature, and probably cloud cover.
Results/Conclusions As a consequence of altitudinal migration by frugivorous birds, elevations also differed in the seasonal abundance of potential seed dispersers. We identified three distinct phenological strategies. Individuals within a species were consistent in their strategy across elevations, and were synchronized in the timing of their reproduction within species. Phenological strategy appears to be quite labile among species of Melastomataceae and Rubiaceae with species in the same genus often varying in strategy. Neither fruit color or crop size was associated with variation in phenological strategy. Species also differed dramatically in their susceptibility to pathogen and seed predator attack and overall, incidence of pathogen attack decreased with elevation. However, we found no consistent differences in pattern of attack with respect to season. These results suggest that phenological strategy is not strongly affected by interactions with seed-dispersing mutualists or seed-depredating antagonists.
