Pacu important in dispersal of plant seeds

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Bigger is better when it comes to fish acting as seed dispersers, according to the results of a recent study.

Mauro Galetti, Camila Donatti, Marco Pizo and Henrique Giacomini studied the role of pacu (Piaractus mesopotamicus) in acting as the dispersal agent for the palm Bactris glaucescens.

The pacu is a frugivorous fish whose diet consisted largely of the palm fruit in the study area (Fazenda Rio Negro, a 7500 ha private ranch in the Nhecolndia region in Brazil, and part of the Brazilian Pantanal).

The pacu is the primary seed disperser of many important fleshy-fruited plants in the gallery forests of the Pantanal, where at least 43 fruit species are fish-dispersed.

The authors caught and dissected 70 fish for their gut contents, and found a significant positive relationship between the presence of intact seeds in fish diet and fish length (meaning that larger fish have a higher probability of dispersing at least one seed), and that bigger fishes tend to carry more intact seeds for dispersal.

The authors mentioned that the effects of overfishing have not been considered a major threat to plant recruitment, but given the results of their study, it is likely that fishermen are selectively harvesting the most important fraction of the fish population for seed dispersal (the larger pacus which are better seed dispersers are not protected from overfishing by Brazilian law).

The authors ...predict that the ongoing overfishing in freshwater ecosystems may collapse effective dispersal of palm species and other taxa that depend on seed dispersal by fishes. Therefore, we suggest that it is paramount to change the attitudes in fisheries management of fruit-eating fishes in freshwater ecosystems, especially in areas where many plant species may rely on fishes for seed dispersal.

The paper is to be published in a forthcoming issue of the journal Biotopica.

For more information, see the paper: Galetti, M, CI Donatti, MA Pizo and HC Giacomini (2008) Big fish are the best: seed dispersal of Bactris glaucescens by the pacu fish (Piaractus mesopotamicus) in the Pantanal, Brazil. Biotropica doi:10.1111/ j.1744-7429.2007.00378.x