Composição funcional em reservatórios : seleção de traços da assembleia de peixes com o envelhecimento.

Abstract

One of the main impacts on aquatic environments is flow regime alteration, usually caused by dam construction. This impact change dynamics and functioning of the environment. We aimed to evaluate changes in the functional composition of fish assemblages of 30 reservoirs, which present different ages. We tested the influence of mesoscale (drainage basins) processes on functional composition of fish assemblages. Then, we assessed alterations on environmental variables (limnological, productivity, morphological) in recent, middle age and aged reservoirs (chronological variable). Finally, we evaluated the relation between functional traits and environmental/chronological variables. Our results show that mesoscale processes affect functional traits abundance in reservoirs. The environmental changes that occur throughout aging process act like environmental filter selecting some functional traits. Hence, in older reservoirs some functional traits, such as omnivorous species, multiple spawning and pelagic were favored while mean size, spine presence, benthopelagic and moderate cryptic behavior were more abundant in recent and middle age reservoirs. Therefore, reservoir age affected the functional composition of fish assemblages in two ways: i) through the effect of the chronological time itself, connected to the river dynamics; ii) through the effect of limnological changes, because over time the reservoirs seem to be in process of trophy degree alteration.