5th International Symposium-Workshop on Frugivores and Seed Dispersal (1985-2010)
According to literature, fishes are believed to be the first vertebrate seed dispersers, yet little research has examined this phenomenon. Ihthyochory has been assumed to be an archaic form of dispersal within primitive angiosperms that has been maintained in inundated tropical regions. The high frequency of ichthyochory is associated with nutrient-poor Amazonian waters, where fish depend substantially on allochthonous material such as seeds and fruits which fall into the water. The homogeneity of the inundated vegetation in Amazonia may be the result of migratory fish dispersing diaspores.
Among them, Characid fishes (Photo : Pacu at Montpellier zoo. (c) PM Forget) are considered to be omnivores; for instance, the frequency of occurrence of items of animal origin was found to be equivalent to that of vegetal origin in the fish Brycon opalinus. These Characid fishes consume fruits and seeds from floodplain forests during the annual flood season, potentially serving as important seed dispersers and predators.
Frugivory and seed dispersal has been especially studied in the piraputanga fish (Brycon hilarii) in the Formoso River, Bonito, western Brazil. The stomach contents of 87 fishes consisted of 24% animal prey (arthropods, snails, and vertebrates), 31% seeds/fruits and 45% other plant material (algae/macrophytes/leaves/flowers); fishes were considered as seed dispersers for eight out of 12 consumed plant species.
In the Amazon, the diet of the frugivorous fish, Colossoma macropomum and Piaractus brachypomus comprised 78-98 percent fruits, largely dominated by a few species. Diets included fruits of 27 woody angiosperms and four herbaceous species from 26 families, indicating the importance of forest and Montrichardia arborescens habitat during peak flood. In a varzea forest of the Rio Madeira in Humaita, Amazonas, 16 out of 33 plant species had seeds or fruits regularly dispersed by fish, and in 17 species the seeds were usually destroyed when eaten.
The role of characid fishes as seed dispersers has also been evaluated in different riverine systems in Central and South America. For instance, authors have demonstrated that seeds of the fig tree Ficus insipida are dispersed by both bats and fishes in riparian habitats at La Selva Selva Biological Station in Costa Rica. In Pantanal, Southern Brazil, the most important food item in the diet of the pacu (Piaracrus mesopotamicus) in the wet season is fruits of the palm Bactris glaucescens which intact seeds were found in large number of the gut of a majority of fishes collected.
Because fruit-eating fishes are often preferred by commercial fisheries, over fishing in freshwater ecosystems as well as deleterious human impacts on aquatic ecosystems worldwide might have major impacts on the dispersal system of fish-dependent plants with unknown ecological consequences for both plant and animal communities.
(Photo: Carrefour in Campo Grande, MS, Brazil. (c) PM Forget)
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