Predation by Rodents and Bruchid Beetles on Seeds of Scheelea Palms on Barro Colorado Island, Panama

Abstract

Predation by rodents on seeds of Scheelea zonensis was studied on Barro Colorado Island, Panama, during the latter half of this palm's fruiting season. The number of Scheelea bearing fruit declined steadily during this period. The proportion of both intact and bruchid-infested seeds among those accumulated under fruiting Scheelea declined, while the proportion of gnawed seeds increased. By early October, 87 percent of the Scheelea seeds sampled had been gnawed by rodents, and few intact or bruchid-infested seeds remained below parent palms. From August through October, agoutis, Dasyprocta punctata, visited Scheelea less and less frequently, while visits by squirrels, Sciurus granatensis, did not dedine. To learn the fate of late-falling Scheelea seeds, we placed small piles of thread-marked seeds, each similar to a small Scheelea fruit crop, in the forest during three successive months, a total of 400 seed each month. Of these 1200 thread-marked seeds, 57.2 percent were retrieved within 20 m of their piles 7 days after placement. Of the retrieved seeds, 22.2 percent were gnawed within 1 m of their pile, 70.6 percent were carried between 1 and 20 m before gnawing, and 7.2 percent were cached (not gnawed, but buried in the ground or covered with litter). More seeds were gnawed, and fewer cached, in September and October than in August. On Barro Colorado Island, intense seed predation by rodents on Scheelea correlates with a previously documented forestwide low in availability of fruits of all kinds, and with a decline in egg laying by bruchids.