A diversidade funcional da assembléia de peixes em uma planície de inundação Neotropical : variações com eventos de El Niño Oscilação Sul (ENSO).

Abstract

Abstract: El Niño Southern Oscillation (ENSO) is a natural phenomenon that generates El Niño and La Niña events worldwide. Among the consequences caused by this climatic fluctuation, there are changes in the rainfall regime, which can trigger in times of extreme drought or extreme flood in freshwater environments, such as floodplains. The floodplain flood phases cause homogenization between the different environments, which also cause the homogenization of the fish assemblage in these floodplains. Among the rivers affected by ENSO is the Rio Paraná and the floodplain associated with its upper stretch, the upper Rio Paraná floodplain (UPRF). We aimed to study if El Niño phenomena change the functional diversity of fish in the floodplain between different environments, lakes and rivers. The results answered the hypotheses that: 1. El Niño events intensify floods in UPRF and, consequently, promote a functional homogenization of the fish assemblage; 2. Different functional guilds will be favored in times of El Niño or La Niña. The measurement of ENSO was obtained by the Oceanic Niño Index (ONI), while the hydrometric level of the upper Rio Paraná was obtained by daily measurement on a hydrometric ruler. The fish were collected with gillnets in different environments of the floodplain, lakes and rivers, being grouped in reproductive and trophic guilds, used to calculate indices of functional diversity. It was tested how ONI affects the hydrometric level of the upper Rio Paraná (Pearson's correlation); how ENSO affects the functional composition of floodplain fish (PCoA; PERMANOVA), as well as the effect of homogenization; which functional guilds are favored in El Niño or La Niña events and whether there is an additive effect of ONI and hydrometric level on the functional composition of the floodplain fish. The hydrometric level presented a positive correlation with ONI, indicating that El Niño events cause flooding in the upper Paraná River, while La Niña drought. The effect of El Niño's functional homogenization on fish was more visible in lakes, with rivers being less affected by ENSO, and floods were not intense enough to homogenize these two types of environment, this may be the same for other floodplains where ENSO acts in the same way. Fish with parental care and invertivores were favored in El Niño events, while herbivorous and piscivorous fish were favored in La Niña events. Migratory fish appears to respond one year after these climatic events, as they have a long-life cycle. The additive effect of ENSO and hydrometric level on the functional composition wasn’t found, because other regional and local factors can influence this interaction. However, even with these factors, the fish assemblage from the floodplain still responds to these climatic fluctuations, being more homogeneous in El Niño events than in La Niña events.