Does the damming of streams in the southern Amazon basin affect dragonfly and damselfly assemblages (Odonata: Insecta)? A preliminary study

Our goal was to investigate whether the loss of riparian forests alters the structure of assemblages and populations of dragonflies and damselflies. We tested the hypothesis that the composition of the odonate assemblages found upstream from dams are significantly different from those found downstream of these barriers. To test the hypothesis, we investigated stream sectors upstream and downstream of three dams located at the extreme of the southern Amazon basin, in the Brazilian state of Mato Grosso. We collected 111 adult odonates, 45 upstream and 69 downstream, representing 18 species, 12 upstream and 10 downstream. The most abundant species was Epipleoneura williamsoni Santos, 1957 (n = 41, 36.9%), followed by Epipleoneura metallica Rcenis, 1955 (n = 20, 18%) and Hetaerina curvicauda Garrison, 1990 (n = 17, 15.3%). Statistical ordination separated the different sectors, with the greatest dissimilarity being found between the upstream and downstream I (DS I), and our hypothesis was further supported by the fact that six of the 18 species recorded in the study did not occur in the upstream sector. As this process may lead to the local extinction of part of the biodiversity of the Amazon-Cerrado transition, even before it is fully understood, we would recommend that the observed pattern be verified through the analysis of other taxonomic groups and on a more ample spatial scale.