Fish functional diversity responses following flood pulses in the upper Parana River floodplain

Flood pulses are the main force driving the dynamics of aquatic communities in floodplains. The responses of communities to environmental changes following flood pulses usually demand a time lag to appear and reach the climax. We assembled a data set of 16years of fish samplings to assess the relationship between water level and four functional diversity measures, in the upper Parana River floodplain. Specifically, we approached four aspects of each relationship between water level and functional diversity: nature (positive or negative), sensitivity (response intensity), responsiveness (response delay) and extent (response duration). The nature of the relationship between water level and functional diversity was positive in all cases. Functional richness (FRic) responded right after flood pulses, although with shorter extent. Abundance-dependent functional measures (evennessFEve; divergenceFDiv; and Rao's quadratic entropyRao's Q) presented delayed responses, reaching peaks more than 1.5years after flood pulses. Significant effects of floods on fish functional diversity were observed for more than 3years, although the highest functional diversity was observed with 1.8years, on average. More importantly, flood pulses had no longer significant effects on functional diversity after 4years. Regarding conservation strategies in regulated systems, flood events should occur every 2 or 3years, with adequate timing (October-November), intensity (up to 450cm) and duration (at least 50 uninterrupted days). Intervals longer than 3years or inadequate timing, intensity and duration could dramatically decrease functional diversity and compromise ecosystem services.