Efeito da seca extrema sobre o espectro de tamanho de peixes em uma planície Neotropical.

Abstract

Body size is one of the most important ecological attributes for biodiversity in aquatic ecosystems. An observed pattern is the inverse relationship between body size and individual abundance, where organisms with larger body sizes are less abundant than smaller ones. Based on this pattern, the effects of extreme drought events were evaluated using a 24-year time series on the size spectrum of fish communities in the Upper Paraná River floodplain (PIARP). The results indicated that drought severity had a significant effect on the size spectrum slope, being more prominent during extreme drought periods, showing a trend of increased abundance of larger individuals in contrast to smaller ones. This pattern is associated with changes in the hydrological cycle that affect reproductive conditions and trophic dynamics but was not directly explained by piscivore biomass. The hydrological reconfiguration caused by dams and intense droughts reduces the presence of juveniles, while larger fish prevail in areas without dams, which is one of the main factors influencing the higher proportion of large individuals. Therefore, the role of extreme droughts in increasing the relative contribution of large individuals during the most critical phases of the hydrological cycle, especially under extreme drought conditions, is highlighted. These results underscore the need for future investigations that incorporate other environmental or biological variables to fully understand the forces shaping the structure of fish communities in floodplain ecosystems.