DOUBLE INSTABILITY GRADIENT IN THE MIDDLE PARANÁ RIVER: ASSESSING AN ECOLOGICAL PATTERN USING BIOLOGICAL TRAITS.

SAIGO, M.; MARCHESE, M.

Valdivia

Congreso; I Congreso Iberoamericano de Limnología y XII Congreso Sociedad Chilena de Limnología; 2016

Environmental stability is a key property of ecosystems because it sets the prevalence of biological or physical determinants of community structure. We hypothesize that in large floodplain rivers there are two opposite instability gradients. The hydrologic instability gradient, which is high in temporarily connected lakes and low in permanently, connected lakes and rivers. The sand bed instability that is high in main channels where hydraulic forces cause the permanent movement of sand dunes, and low in small rivers and lakes. In the present study we tested three hypotheses H1: Inter-specific competition structures communities in permanently connected lakes and small rivers, H2: In large rivers communities are not structured by competition but by sand bed instability. H3: In temporarily connected lakes communities are not structured by competition but by hydrologic instability. We sampled benthic invertebrates in 30 sites of the Middle Paraná River-floodplain system, analyzed co-occurrence patterns and traits-type of site relationship by RLQ and fourth corner method. We performed an RLQ analysis to show the relationship between site type (R matrix) and traits (Q matrix) by means of species abundances per site (L matrix). Observed co-occurrence patterns were according to the hypotheses. Similarly, there was a global significant relationship between traits and type of sites (p