Seed dispersal of a high quality fruit by specialized frugivores: high quality dispersal?

摘要

Dispersal quality, as estimated by the cumulative effects of dispersal, germination, seed predation, and seedling survival, was examined for Beilschmiedia pendula (Lauraceae) in Monteverde, Costa Rica. I determined the pattern of dispersal by finding seeds deposited by birds, protected the seeds from seed predators with cages to assess germination and seedling survival, and examined seed predation rates with marked seeds. Seed predation, germination, and seedling survival were compared between seeds naturally dispersed by birds and seeds placed at randomly located sites. Approximately 70 percent of seeds dispersed by birds (N = 244) were deposited < 10 m from crown edges of fruiting B. pendula trees, although some seeds were dispersed at least 70m away. Larger seeds were more likely to be dispersed under or close to the parent trees, and larger seeds produced larger seedlings, Seed size was not correlated dispersed under or close bo the parent trees, and larger seeds produced larger seedlings, Seed size was not correlated directly with seedling survival, but larger seedlings at three months were most likely to survive one year. Seed predation by mammals and insects and seedling mortality due to fungal pathogens were concentrated beneath the crowns of parent trees. Seedlings and saplings were more abundant beneath fruiting B. pendula trees, but individuals farther away were taller on average. Thus, dispersal is beneficial for B. pendula, but such benefits appear most pronounced at a small spatial scale; seeds dispersed > 30 m from the crown edges actually had a lower probability of survival than those dispersed 10-20 m. Only 10 percent of Bpendula seeds received high-quality dispersal in terms of landing in the zone with the highest per seed probability of seedling survival 10-20 m from parental crowns.