Seed dispersal and predation by spiny rats (Proechimys semispinosus) and red-tailed squirrels (Sciurus granatensis) were studied in five forest gaps and adjacent intact forest on Barro Colorado Island, Panama, during June and July 2003 and January 2004. The objectives of this research are to determine, within contiguous forest, 1) abundances of P. semispinosus in understory and tree-fall gaps, 2) rates of seed removal in those habitats by both spiny rats and red-tailed squirrels, and 3) the fates of removed seeds. Live trapping on grids was used to estimate the abundances of rats in both habitats and was conducted during 10 nights at the beginning of each field season. We captured 75 individual spiny rats (58 in forest gaps and 17 in intact forest). To address the removal and dispersal of seeds, semi-permeable wire mesh exclosures were set at randomly selected stations within the trapping grids. These exclosures allowed the entry of spiny rats, squirrels, and other small rodents but excluded larger granivorous mammals. Seeds were marked with pieces of string that were dusted with fluorescent powder and tracked at night with an ultraviolet light.

Results/Conclusions

Spiny rats were clearly more abundant in tree-fall gaps than in the understory. Of the 75 individuals captured, 77.3% were captured in gaps. A total of 304 seeds was removed (159 in forest gaps and 145 in understory). Spiny rats removed more seeds from gaps, and squirrels removed more seeds from intact forest. Both species dispersed more seeds during the rainy season than during the dry season. Squirrels dispersed seeds farther than did spiny rats. Due to their foraging behavior and association with gaps, spiny rats may disperse seeds from intact forest into gaps. This directed dispersal could have important implications for gap-specialist trees and also for other plant species that are shade-tolerant but benefit from exposure to increased sunlight in forest clearings.