Food partitioning among some characids of a small Brazilian floodplain lake from the Paraná River basin

Resource partitioning and the seasonal patterns of food intake of four characids (Astyanax fasciatus, A. bimaculatus, A. schubarti and Cheirodon stenodon) were studied during 1988 in a floodplain lake of Mogi-Guacu River, Sao Paulo State. For interspecific comparisons, data of the previously studied Moenkhausia intermedia have also been used. A. fasciatus and A. bimaculatus can be considered omnivorous species, while A. schubarti and C. stenodon are predominantly herbivorous. The river flood cycle (following the wet season October-March and dry season April-September) seems to influence both seasonal food intake and food overlap between species. February-March and September-October are probably the months of highest food availability, and the months preceding these periods have the lowest resource amount. Our study shows that both omnivorous and herbivorous species modified the intensity of their interactions according to this cycle. Omnivorous species maintained fairly segregated diets when resources were presumably limited, and showed a rapid change from distinct food niches in the dry season to widely overlapping ones when resources were presumably more abundant. Conversely, the herbivorous species showed higher overlap during the dry season. Acute cyclic changes in the environment, as observed in this study, suggest the necessity of small interval sampling in food partitioning studies in tropical freshwater floodplains, in order to understand how species interact and cope with changes in food availability.