EFFECTS OF TEMPORAL CHANGES ON RESOURCE AVAILABILITY IN THE DIET OF Astyanax paranae (PISCES, CHARACIDAE) IN TROPICAL HEADWATER STREAMS
We assessed the effects of variation in availability of allochthonous detritus between seasons on the microscopic and isotopic diet of the dominant omnivorous fish species Astyanax paranae Eigenmann, 1914 to test the hypothesis that their diet is mainly driven by the availability of allochthonous resources in low order streams of the Brazilian savannah. We measured the biomass of the litter benthic stock and analyzed the gut content and C and N isotope ratios in muscle tissue of individuals in dry and rainy seasons in three forested headwater streams. Algae obtained by scraping submerged rocks and leaf litter were used as potential food sources of the fish species. Astyanax paranae had similar isotopic signatures in dry (δ13C = -25 ‰ ± 2.4; δ15N = 7.5 ‰ ± 1.2) and rainy season (δ13C = -25 ‰ ± 0.8; δ15N = 7.3 ‰ ± 1.0). Despite the increase in consumption of allochthonous items during the dry season, autochthonous carbon is the predominant resource for A. paranae in all streams and seasons. Tracing resource availability and the use of resources by A. paranae indicated that the aquatic food web depends not only on terrestrial but especially on aquatic carbon sources and that the diet of species is independent of the availability of resources. These findings show the importance of autochthonous sources for the maintenance of carbon flow in such fragile ecosystems and reinforce the need for further studies related to the main basal carbon source and productivity of tropical aquatic food web structure in tropical savannah streams.