Seed and Early Seedling Predation in the Forest Understory and in Treefall Gaps

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Seed dispersal may reduce seed and seedling predation (sensu Janzen) either by removing propagules from a zone of extremely high mortality near the parent, or by carrying the seeds to a habitat with reduced predation. Using the neotropical subcanopy tree Faramea occidentalis (L.) A. Rich (Rubiaceae), I experimentally investigated the effects of dispersal to treefall gaps and dispersal within the forest understory on seed and early seedling predation. In the forest understory, seeds 5 m from the crown of an adult F. occidentalis suffered significantly less predation by mammals than did seeds beneath fruiting conspecifics, but the losses of young, establishing seedlings were equivalent beneath and away from adults. In contrast, seed predation in treefall gaps was indistinguishable from predation beneath fruiting F. occidentalis, while seedling predation in gaps was even greater than beneath conspecific adults. Dispersal within the forest understory appears to be selectively advantageous because of decreased seed predation away from parent trees. But the overall consequences of dispersal to gaps are less certain. Although the high light environment of a gap enhances seedling growth, the extreme predation on seeds and young seedlings may make successful establishment in a treefall gap an extremely unlikely event.