Fishers' Knowledge Reveals Ecological Interactions Between Fish and Plants in High Diverse Tropical Rivers

Frugivory and seed dispersal by fish is an important mutualistic interaction in complex and species-rich tropical rivers. The local ecological knowledge (LEK) held by fishers can provide new information on relationships between fishes and plants in less studied rivers. This study aims to investigate the feeding interactions between frugivorous fish and plants through interaction networks based on the fishers' LEK in three rivers in the Brazilian Amazon (Negro, Tapajós and Tocantins). A total of 418 fishers were interviewed in 24 communities (eight in each river). The studied fishes were tambaqui (Colossoma macropomum), matrinxã (Brycon spp.), pacu (Myloplus spp.), pacu manteiga (Mylossoma duriventre), pirapitinga (Piaractus brachypomus), and jaraqui (Semaprochilodus spp.). The interviewed fishers cited a total of 92 plants consumed by the six frugivorous fishes in the three rivers. The interaction networks showed a higher nestedness in the Tocantins, greater connectance and modularity in the Tapajós and more specialization in the Negro, where the protected areas may have contributed to a more complex and specialized interaction network. The more nested network in the Tocantins River indicated the loss of specialized interactions in disturbed communities. The Tapajós River network showed the highest number of interactions between fish and plants, but this river has been threatened by environmental changes. Fishers' LEK associated to network analyses can advance our understanding on ecological interactions. This approach can be also useful to evaluate and mitigate ecological effects from anthropic changes in the Amazon and other high diverse tropical rivers.