Estequiometría ecológica y homeostasis en la red trófica de un río pampeano rico en nutrientes

FEIJOÓ CLAUDIA SILVINA; LEGGIERI LEONARDO RAMÓN; OCÓN CAROLINA; RODRIGUES-CAPÍTULO ALBERTO; GIORGI ADONIS DAVID NAZARENO; COLAUTTI DARÍO; MUÑOZ ISABEL

Guimaraes

Congreso; XVI CONGRESS OF THE IBERIAN ASSOCIATION OF LIMNOLOGY; 2012

The theory of ecological stoichiometry generally accept that heterotrophs display a higher degree of stoichiometric homeostasis than autotrophs, which tend to closely follow the variation of dissolved nutrient concentration. In this study, we analysed the elemental content [carbon (C), nitrogen (N), and phosphorus (P)] and the stoichiometric ratios (C:N, C:P and N:P) of organisms from different trophic levels (producers, macroinvertebrates, and fishes) of an enriched Pampean stream during 22 months. We investigated whether P and N contents of the biota were consistently higher than in other systems with lower nutrient conditions. The effects of additional enrichment on the stoichiometry of the biota was analysed by a fertilization experiment. The degree of homeostasis was determined in pairs of organism-reso urce, which were established by stable isotopic signatures, analysis of gut content in macroinvertebrates, and field and bibliographic information.The organisms were generally more enriched in P than in C and N when compared with other stream biota. Epipelon and epiphyton were the only primary producers that responded to the enrichment through an increase in their P content and a decline of the stoichiometric ratios. Increases in P content were also observed in macroinvertebrate scrapers, filterers and predators but they were not reflected in concomitant changes in the stoichiometric ratios. We can conclude that the biota of the Pampean stream generally showed a high P content and a substantial degree of stoichiometric homeostasis in all trophic levels. Both features explain the lack of response to the moderate P addition in most producers and consumers.