Comparisons of Seed Predation in Tropical, Tidal Forests From Three Continents

An inverse relationship between the amount of seed predation and the dominance of a tree species in mangrove forest canopies has been hypothesized based on field studies conducted in Australia (Smith 1987a). Seed predation experiments have recently been performed in mangrove forests of North America (Florida and Panama) and southeast Asia (Malaysia) on several species of Avicennia, Bruguiera, and Rhizophora. The results of these experiments are compared with additional data from Australia to test the generality of the dominance-predation model. Significant differences were found in the amount of predation on four species of Avicennia. All Avicennia were consumed in greatest quantity where they were rarest in the forest canopy and in least amounts where they dominated the canopy. Consumption of Rhizophora apiculata in Australia and Malaysia followed patterns similar to that for Avicennia. For R. mangle, however, contradictory results were obtained. No R. mangle were eaten in Florida. In Panama, more were consumed where this mangrove dominated the canopy compared to a forest where it was rare. Results for Bruguiera cyclindrica in Malaysia supported the dominance-predation model, whereas results from Australia for B. gymnorrhiza did not. Data for Acicennia clearly support the dominance--predation model. Regardless of species, seed predators exert an influence on the distribution of Avicennia in mangrove forests. Variation in the amount of predation on Rhizophora among regions is partly attributable to differences in the composition of the predator guilds between the forests studied. Predator guilds in the Malaysian and Australian forests are dominated by grapsid crabs. In Florida, crabs are minor consumers of propagules and three genera of snails are most important. Seed predation is variable among forests. The effect of seed predators on mangrove forests is related to the type of mangrove tree and composition of the seed predator guild.