Partição de recursos alimentares de peixes durante evento climático extremo

Abstract

Determining the use of the food niche among species that coexist in the same environment under extreme climatic conditions is essential to understand what responses consumers will make to adjust their foraging behavior. In the present study we investigated how the diet of small characids that inhabit the Middle Uruguay River and which are morphologically very similar behave in conditions of severe drought resulting from the La Niña Phenomenon. We tested the theory of optimal foraging by estimating changes in diet breadth and niche overlap between species. For this, the present study used 2.711 individuals belonging to 6 species of small characids. The lower region of the Ibicuí River, the stretch studied in the present work, is characterized by being a plain region where some lentic environments such as lagoons can be found along with the main lotic channel. This stretch was separated into two sampling sites, where collections were carried out between these biotopes: main river and lagoon. Sampling was carried out monthly in 2020, totaling 12 months of sampling. For collection, a trawl net was used as a fishing device. Most of the small characids were captured in the lagoon biotope. The analysis of the stomachs indicated that the species' diet was very diverse, reaching 36 food items and that the species fed mainly on autochthonous items. Despite being diverse, the largest volume of the diet consumed was concentrated in a few autochthonous food items, with emphasis on filamentous algae and microcrustaceans. The presence of allochthonous organisms, although present, has decreased significantly in the last seasons of the year. These conditions were observed in both fish captured in the lagoon biotope and in the river biotope. Our findings advance knowledge of how morphologically similar fish respond to severe conditions of prolonged drought. Findings from this study (such as high dietary overlap between sympatric species and a diet consisting mainly of a few items) may be useful in predicting how Uruguay River basin fish will respond to extreme weather conditions that may be more common in the future.