Frugivorous animals function as dispersal agents for many plant taxa around the world. Mutualistic relationships between frugivores and plants are particularly common in tropical forests. Unlike temperate ecosystems, where growing seasons are shaped by abiotic constraints, many tropical ecosystems are relatively aseasonal. Consequently, some tropical plants have evolved to reproduce subannually – i.e. multiple times per year. Temporal variation in fruit/seed resource production (e.g. masting species) is known to have an important influence on the functional and behavioral responses of seed dispersers and seed predators, yet these dynamics are relatively unknown in systems with subannual resource production. Muskwood (Guarea guidonia) is a dioecious mahogany tree widely distributed in Neotropical humid forests. In the Dominican Republic, populations flower in multiple discrete episodes, and fruits take 8-10 months to mature over an extended fruiting period (January-August). Beginning in 2016, I monitored 48 focal trees to observe flowering and fruit development continuously until fruits matured in 2017. I sampled frugivorous bird foraging activity at fruiting trees over the course of the fruiting period(s) (152 total hours), simultaneously measuring focal tree ripe fruits and neighborhood (15-m radii) fruit abundance to determine their effects on frugivore visitation.
Results/Conclusions
Flowering was observed in four discrete synchronous episodes between May–December in the study population with most individuals flowering during the first two episodes (May & July). These flowering patterns corresponded to a single, extended fruiting period March–September of the following year with high variability in the timing of initial fruit ripening and the period over which focal trees had ripe fruits. Neighborhood fruit abundance was a poor predictor of seed disperser attendance. Instead, the best model included an interaction effect between focal tree fruit count and date. Specifically, resource abundance at the scale of the focal tree had a negative or neutral relationship with frugivore attendance but became increasingly more positive as the season progressed. While fruit abundance at the scale of the neighborhood did not affect foraging activity at the focal trees, other data collected from seed trap samples in the landscape suggest that frugivorous birds switched to alternative fruit resources of co-fruiting species at least once during the fruiting period. By allocating reproductive investment into multiple flowering episodes, subannual reproduction may balance the trade-off between energetic investment in fruits and the fitness benefits of dispersal.