Impact of Mammals on Early Recruitment of a Tropical Canopy Tree, Dipteryx panamensis, in Panama

On Barro Colorado Island, Panama, the canopy tree Dipteryx panamensis (Pitt.) Rec. & Mell (Leguminosae) is a critical food species for the animal community, because it fruits during a season of food scarcity for frugivorous mammals, some of which act as seed predators on Dipteryx. In 1981, seed losses to mammal seed predators were extremely high at fruiting Dipteryx trees on Barro Colorado in comparison to an adjacent mainland area where these mammals appear to be less abundant. Seed removal experiments suggested that seed dispersal did not confer greater escape from this intense seed predation, at least at moderate distances from fruiting trees. The cotyledons of newly-germinated seedlings were also eaten and seedlings were killed in the process, thus few seedlings naturally survived to an established stage. Seeds protected from mammals showed extremely high germination and establishment success. Survival of established seedlings after 13 months was lowest under Dipteryx crowns (12 %), intermediate under the shade of other trees (32 %), and highest in small light gaps (74 %), and only the seedlings in light gaps grew significantly. Eventual regeneration of this tree may depend upon the presence of established seedlings or saplings in the understory when canopy gaps form. Intense seed predation on Barro Colorado restricts the establishment of such seedlings and saplings in comparison to other areas where mammals appear less abundant. While the high Dipteryx seed losses support assertions that Barro Colorado's mammal populations are unusually abundant relative to other Neotropical areas due to release from regulation by carnivores, it may be that reductions in mammal populations in other areas due to hunting by humans may exaggerate apparent differences between these areas and Barro Colorado.