Mudanças temporais na precipitação afetam a composição taxonômica e funcional de assembleias de peixes em igarapés da Amazônia central

Abstract

The effects of climate changes in local assemblages are poorly known. In the Amazon basin, changes in the rainfall pattern in the last decades are expected to affect the hydrological dynamics of forest streams, which strongly depends on the local rainfall regime. Such changes may alter limnological and structural characteristics of the streams and, consequently, disturb local fish assemblages. Here we present results of four repeated surveys of stream fish assemblages conducted along a time interval of 17 years (2001-2018) to investigate the dynamics of fish taxonomic and functional composition and the possible influences of local hydrological regime changes. Fish samplings and environmental variables measurements were conducted with a standardized protocol. Temporal changes in the taxonomic and functional composition of fish assemblages among the four surveys were evaluated regarding its magnitude, direction and congruence of trajectories along time. Throughout the two last decades, the total annual rainfall increased, and stormy days (with rainfall greater than 20mm) were more frequent. The taxonomic and functional composition of local fish assemblages changed among the four surveys, and differences were stronger between the first (2010) and last (2018) surveys. Changes in fish assemblages affected the relative abundance of some of the most abundant species and were apparently mediated by alterations in the substrate composition (i.e. shifting from predominantly covered by litter banks to open sand). Functional changes were associated to traits related to food acquisition, locomotion and habitat use, resulting in lower relative abundances of species that occupy open water habitats in the stream channel and higher abundances of species able to use the lateral ponds and shallow marginal areas. These results provide evidence of a directional change in fish assemblage composition resulting from the effects of increased precipitation and a higher frequency of stormy days over the last decades. Considering the short time interval evaluated and the subtleness of the climatic changes analyzed in this study, these findings can be surprising and point out to the need for the maintenance of long-term ecological research programs in tropical regions, which concentrate most of the planet’s biodiversity.