Seed dispersal by a Neotropical fruit-eating fish.
Anderson, Jill*,1, Saldana Rojas, Joe2, del Busto Rojas, Cahuide 3, 1 Cornell University, Ithaca, NY, U.S.A.2 Instituto para Investigaciones de la Amazonia Peruana, Iquitos, Loreto, Peru3 Universidad Nacional de la Amazonia Peruana, Iquitos, Loreto, Peru
ABSTRACT- Yearly, Peruvian floodplain forests inundate for up to 6 months. During this time, frugivorous fishes congregate beneath trees and consume fruits that fall into the water. Fruit-eating fishes are vital to South American fisheries and are highly susceptible to overexploitation, yet few studies have explored the interactions between fishes and floodplain forests. Fishes clearly rely on flooded forests for food; the question remains to what extent these forests rely on the seed dispersal services of fruit-eating fishes. We are testing the hypothesis that seed dispersal by fish is critical to the regeneration ecology of floodplain forests. During part of the flooded season of 2004, we found viable seeds of 11 species of floodplain trees from the digestive systems of 67 individuals of Colossoma macropomum (Characidae). High quality seed dispersal depends both on the transport of seeds to sites suitable for seedling growth and on the enhanced germination success of gut-processed seeds. To address these issues, we have initiated a radiotracking study to assess movement patterns of fish and a greenhouse experiment to analyze the vigor of gut-passed seeds. In 2004, we followed 5 radiotagged C. macropomum in Pacaya-Samiria National Reserve to evaluate the distance and the directionality of seed dispersal by fish. Data from these five individuals indicate that large fruit-eating fishes potentially disperse seeds long distances; e.g., one fish moved more than 8 km in 3 days. Movements were generally constrained to the flooded forest and not the river channel. Seed dispersal by fish may differ fundamentally from dispersal by water; the water current would disperse seeds unidirectionally downstream, whereas fish in our study moved upstream and between small tributaries. Additional fish are being radiotagged during this flooded season (March-July 2005) and these data will also be presented. Finally, in 2004, seeds of Cecropia membranacea germinated significantly faster after gut-passage by fish than seeds that were left in fruit pulp; however, seeds removed from the pulp manually did not differ significantly from those passed by fish. Therefore, the primary role of fish may be to remove fruit-pulp from seeds and to carry seeds against the prevailing water current. Results from 2005 will complement these preliminary 2004 data.
Key words: seed dispersal, Neotropics, floodplain, fruit-eating fish
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