Abstract. 1. The Amazon region is formed primarily by a dense network of acid and nutrient-poor streamlets. The stability of environmental conditions coupled with spatial constraints to dispersal turns these streamlets into an interesting arena to compare neutral and niche drivers for community organisation. Here, we evaluated the relative importance of local environmental conditions and regional dispersal limitation to determine beta-diversity and distributional patterns of species richness of the adult Odonata assemblage present in the Adolpho Ducke Forest Reserve (Manaus, Amazon) river basins.
2. Samples were taken in 24 streamlets distributed in four river sub-basins (pairwise distances up to 10 km) during the rainy season. The samples consisted of visual surveys for adult individuals of Odonata present in 100 m transects along each streamlet; each transect was divided into 20 segments of 5 m.
3. A total of 17 species were observed and 23 (±4.8) were estimated using a jackknife procedure. Four sub-basins were statistically similar based on species richness and beta-diversity. Distance among the streamlets had a low predictive power for species richness, while beta-diversity patterns were mainly explained by local environmental variables (channel width and depth). The low values of the beta-diversity index may be attributed to the high similarity of the environment, which presented little variation in abiotic conditions.
4. Low dispersal constraints and environmental stability are the primary explanations for low beta-diversity at this spatial extension. Nevertheless, the importance of local environmental variables to determine beta-diversity suggests its inclusion as criteria for setting conservation priorities for this group.