Evidence for dispersal of fig seeds by the fruit-eating characid fish Brycon guatemalensis Regan in a Costa Rican tropical rain forest

Abstract

Studies were conducted at the La Selva Biological Station in the Atlantic lowlands of Costa Rica and in a greenhouse in California to assess the potential role of a Neotropical fish in dispersing the seeds of a rain forest tree. Feeding experiments showed that the seeds of Ficus glabrata H. B. K., a major, canopy-forming riparian tree, require approximately 18–36 h to pass through the digestive tract of Brycon guatemalensis Regan, an abundant riverine fish whose adult diet consists largely of leaves and fruits of this fig tree. The seeds were still viable after passing through the fish’s gut but germinated somewhat more slowly than seeds that had been left in the fig exposed to air or floated in water. Stem elongation of seedlings from seeds that had passed through the fish’s gut was faster than that of seeds in the other two treatments. Placement of seeds upstream may be more important than enhanced germination for plants such as Ficus that produce large numbers of seeds. Radio telemetry showed that five of six tagged fish had moved distances of 0.1–1 km upstream; seven other fish with transmitters, including three large males, were not relocated and may have moved into tributary streams for spawning or feeding. These findings suggest that Brycon can disperse large numbers of Ficus seeds and help maintain the upstream populations of the tree.