Streams dry and ecological uniqueness rise: environmental selection drives aquatic insect patterns in a stream network prone to intermittence

The study of variation of species composition among sites is key to understanding community ecology, but few studies have assessed beta diversity patterns in highly dynamic stream networks in the Neotropical region. We assessed aquatic insect patterns of local contribution to beta diversity (LCBD) and species contribution to beta diversity (SCDB) in a Neotropical drainage network composed of both perennial and intermittent streams in a dry period. We evaluated if environmental and/or spatial predictors drive patterns of LCBD. We sampled aquatic insects in 12 intermittent headwater streams and 34 perennial streams. The intermittent compared to perennial streams had higher LCBDs and lower richness. The pure environmental component significantly explained 19% of the variation of LCBD, while the pure spatial components were not significant. Forty-six taxa contributed to beta diversity above the mean of the 199 taxa. We detected the association of oxygen tolerant and good dispersal ability taxa to intermittent streams and species riffle-adapted taxa as indicators of perennial streams. We showed a disproportional contribution of intermittent streams to the regional species pool. In summary, we demonstrated that when streams dry out, compositional uniqueness may increase during the dry period making them critical to conservation planning of dynamic stream networks.