Effects of pre-dispersal seed predation and fungal infection on seed production and seed survival of the pioneer tree Luehea seemannii in Panama

Background/Question/Methods

Pre-dispersal seed predation is a major cause of seed losses in tropical plant species. Pre-dispersal seed predators are often insects, but also may also include vertebrates such as monkeys and parrots. Fungal pathogens have also been directly implicated in seed losses at the pre-dispersal stage, but successful fungal infection may depend on initial damage to seed protecting structures by seed predators. In this study, our objectives were (1) to quantify pre-dispersal seed predation and fungal infection in a common neotropical pioneer tree species, Luehea seemannii (Tiliaceae), that produces dehiscent capsular fruits and wind-dispersed seeds, and (2) to link pre-dispersal effects on seed quality to post-dispersal survival of seeds in the soil. To examine how seed predators and fungi influence seed losses, insect mesh exclosures, fungicide and the combination of both treatments were applied to separate Lueheabranches in the canopy of three and four trees at Gamboa and Metropolitano Park, Panama, respectively. To determine if treatments affect seed viability and survival in the soil half the seeds collected from each treatment were buried for four weeks in the forest soil and germination tested before and after breaking dormancy in a growing house.

Results/Conclusions

Overall, 24% of developing fruit were lost to insect attack and an additional 23% of fruit were aborted for unknown reasons. In contrast, only 2% of seeds were infected by fungi at the pre-dispersal stage. For seeds germinated directly after collection, fungicide significantly increased germination after breaking dormancy, with a greater effect at the wetter site (Gamboa). For seeds that were buried in the soil, treatments and site did not affect germination, but the pre-dispersal insect exclosure treatment increased the fraction of seeds that were dormant. This result suggests that exposure to insect predators may cause physical damage to seeds that results in the loss of physical dormancy but does not increase the susceptibility of seeds to pathogen attack in the soil.