No abstract

SynopsisThe feeding ecology of three characids ( A . fasciatus, A. bimaculatus and A. schubarti) was studied monthly during 1988 in Lake Inferngo, a major floodplain lake of the Mogi-Guaqu River in the State of SBo Paulo. River flooding directly influenced the diet of the omnivorous A. bimaculatus and A. fasciatus which responded to maximum inundation (March) by consuming predominantly allochthonous insects. In contrast, A. schubarti was less influenced by the river flood cycle on qualitative changes in diet and relied basically on aquatic macrophytes and periphytic algae. The importance of zooplankton in the diet of the three species was low, and may be attributed to its low density in the water column (< 1 ind 1.'). Ontogenetic diet changes were evident for the three species. For A. fasciatus and A. birnaculatus the importance of zooplankton was high at the early stages, decreasing with size. A. schubarti at younger stages consumed diversified items which gradually decreased quantitatively up to the size class of 65 mm; from this size onwards, the diet became restricted to the consumption of periphytic algae and macrophytes.

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 MogiGuacu 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 .