The response of fish functional diversity to the El Nino Southern Oscillation (ENSO) in a Neotropical floodplain

We aimed to study the responses of fish functional diversity to El Nino Southern Oscillation (ENSO) in different environments from the upper Parana River floodplain (UPRF), Brazil. We predicted that (i) El Nino events intensify floods in the UPRF and, consequently, promote functional convergence of the fish assemblage and (ii) different functional traits will be favored in El Nino or La Nina events. The functional convergence was measured through functional dispersion and functional redundancy indexes, wherein lakes presented higher similarity during El Nino and lower similarity during La Nina. ENSO did not have a strong effect in rivers. The functional richness and functional evenness did not respond to ENSO events. Fish with parental care and invertivorous fish were favored during El Nino, while piscivorous and herbivorous fish were favored during La Nina. Due to their distinct lifecycles, long-distance migratory fish responded to this climatic oscillation 1 year after El Nino. Overall, the influence of ENSO on fish diversity in the UPRF is a complex phenomenon. However, even with other local and regional factors acting on the ichthyofauna, fish diversity responded to these climatic fluctuations.

Automated summary

The study found that El Nino events intensify floods in the upper Parana River floodplain, leading to functional convergence in fish diversity, while different functional traits are favored in different ENSO events. Fish assemblages show varied responses to functional diversity during ENSO events.