Within Flood Season Variation in Fruit Consumption and Seed Dispersal by Two Characin Fishes of the Amazon

Many Amazon River fishes consume fruits and seeds from floodplain forests during the annual flood season, potentially serving as important seed dispersers and predators. Using a participatory approach, this study investigated how within-season variation in flood level relates to fruit consumption and seed dispersal by two important frugivorous fish, Colossoma macropomum and Piaractus brachypomus, in two Lower Amazon River fishing communities in Brazil. Diets of both fish species were comprised of 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. A correspondence between peak fruit species richness and peak flood level was observed in one of two communities, which may reflect higher forest diversity and/or differences in selection of fishing habitat. Both fishes are seed dispersers and predators, the relative role of which did not vary by flood level, seed size, or fish size, but may vary with seed hardness. Interspecific differences in diet volume and intact seeds suggest P. brachypomus are more effective seed dispersers than C. macropomum. Overall, the spatial and temporal variation in fruit species composition and richness demonstrate plasticity in fruit consumption in relation to flood level and locally available fruits. While such diets are adaptive to the dynamic changes of Amazon floodplain habitats, the high consumption of forest fruits and seeds from mid- and late-successional species suggests that floodplain forest degradation could disrupt seed dispersal and threaten local and regional fisheries. RESUMO Muitas especies de peixes da bacia Amazonica se alimentam de frutos e sementes da floresta durante o periodo anual de inundacao, funcionando como dispersores e predadores de sementes. Nesta pesquisa, utilizando uma metodologia participativa, se estuda a relacao entre o nivel do rio e a dieta por dois importantes peixes frugivoros, Colossoma macropomum e Piaractus brachypomus, avaliando seu papel na dispersao de sementes em duas comunidades ribeirinhas do Baixo Amazonas do Brasil. As dietas se constituiram de 78–98 porcento de frutos, sendo dominadas por poucas especies. As especies incluiram 27 angiospermas lenhosas e 2 herbaceas pertencentes a 24 familias, indicando a importância da floresta e do aningal durante o periodo da inundacao. A hipotese da ocorrencia de um pico na riqueza dos frutos durante o pulso hidrico so foi observado em uma das duas comunidades, que talvez possa indicar uma maior biodiversidade da floresta e/ou diferencas em selecao de habitat da atividade pesqueira. As duas especies de peixes sao dispersores de sementes, o papel relativo de tal nao foi correlacionado com o nivel do rio, peso da semente, ou tamanho do peixe, mas talvez com dureza da semente. As diferencas intraespecificas em volume e contagem das sementes sugerem que P. brachypomuse um dispersor mais eficiente que C. macropomum. A variacao temporal e espacial na composicao dos tipos de frutos consumidos confirmam a plasticidade da dieta destas especies relacionadas ao nivel do rio e frutos disponiveis. Enquanto que as dietas sao adaptatacoes a dinâmica da varzea, o alto consumo de frutos e sementes de estagio medio e avancado de successao sugere que o desmatamento pode interromper a dispersao das sementes e ameacar a pescaria local e regional.