Insights Into Focal Seed-Dispersal Systems on Barro Colorado Island

Mckey (1975) hypothesized that animal-dispersed tropical plants produce either relatively few seeds with rich fruit rewards that attract specialist consumers or relatively many seeds with inexpensive rewards sought by generalist opportunists. These ideas have been investigated on Barro Colorado Island in studies of focal seed-dispersal systems, defined as a tree species and the assemblage of animals that consume fruits and disperse or fail to disperse seeds. Virola sebifera and V. surinamensis produce small crops of protein- and fat-rich fruits that attract a few obligate fruit-eaters. Most trees are depleted of ripe fruits daily. Guarea guidonia and Protium stevensonii (syn. Tetragastris panamensis) produce superabundant fruits of low nutritional content that attract opportunistic vertebrates consistent with the generalist paradigm. Studies of seedling recruitment show that dispersal away from parents is of critical importance in Virola surinamensis but not in Protium stevensonii. These studies illustrate the strategies and rewards of seed dispersal among tree species.