Fish communities in floodplain lakes depend heavily on the surrounding floodplain vegetation as the complex hydrological dynamics seasonally inundate extensive areas of land. Consequently, land-use change poses a significant threat to floodplain biodiversity by altering the natural sources of energy that sustain these systems. This study investigated the influence of human land use and seasonality on the trophic structure of floodplain fish assemblages. Additionally, we will compare the trophic metrics calculated considering all sampled species (method I) with those derived from a standardized group considering only species sampled in both seasons (method II). Fish were sampled in five floodplain lakes and analyzed for nitrogen and carbon stable isotopes. Our findings indicated that seasonality was a key determinant of the nitrogen range used by fish and species’ niche areas. In contrast, human land use was associated with the niche size, carbon range, and trophic diversity of the fish assemblage. Moreover, the trophic metrics estimated for the standardized group of fish were more sensitive to environmental changes than those calculated for all sampled species, likely due to random sampling effects. These results highlight that human land use reduces the role of natural hydrological dynamics in shaping the trophic structure of fish assemblages. Therefore, conserving riparian vegetation in floodplains is crucial for preserving aquatic consumers, as this vegetation plays a vital role in maintaining floodplain biodiversity. • Both land use and seasonality drive the trophic structure of fish assemblages. • Brazilian floodplains have been increasingly occupied by human activities. • Human land use is determining the resource range of fish assemblages and reducing the influence of seasonality. • A standardized group of fish is a better indicator of changes in trophic structure.
Urbano et al. (Wed,) studied this question.