Influence of landscape homogenization due to river damming on dragonfly (Odonata) community structuring in a subtropical forest in the southern Atlantic Forest

Human activities affect the structure, dynamics and energy flow of aquatic ecosystems. River damming, a common anthropic impact in Brazil, changes solar incidence, water flow and temperature of waterbodies, thereby affecting their fauna. Due to their high sensitivity to environmental changes, the Odonata may be indicators of these impacts. We sampled two ecologically distinct sites, (1) a quasi-pristine forested area and (2) a nearby human-impacted reservoir landscape, to evaluate the effects of damming on odonate community structure. The species composition of quasi-pristine communities was more heterogeneous and differed almost completely (indicating high turnover) from that of the reservoir-area communities. The capacity of the reservoir to maintain local fauna was almost nil. The communities in the changed landscape had the highest local diversity, which is related to the high occurrence of widespread generalist South American species. We also tested two recently proposed bioindication ratio tools based on the richness or abundance of high-level taxonomic categories; both effectively reflected the extent of the impacts of damming. The best performing ratios were Coenagrionidae/other Zygoptera richness ratio, Zygoptera/Anisoptera abundance ratio and Libellulidae/other Anisoptera richness ratio. The reservoir landscape promotes biotic homogenization. However, the water supply system entails the preservation of part of the native habitat in its surrounding areas, consequently maintaining forest-dependent biodiversity in quasi-pristine environments.

Automated summary

Human activities have significant impacts on the structure, dynamics, and energy flow of aquatic ecosystems. Damming rivers in Brazil, a common anthropic activity, alters solar incidence, water flow, and water temperature, which in turn affects the fauna in waterbodies. Odonata, due to their sensitivity to environmental changes, can serve as indicators of these impacts. This study evaluated the effects of damming on odonate community structure by sampling two ecologically distinct sites in Brazil. The results showed that damming led to a significant change in species composition and reduced local fauna diversity in the impacted reservoir landscape. Additionally, two bioindication ratio tools based on taxonomic categories effectively reflected the extent of damming impacts. The findings highlight the importance of considering the effects of damming on aquatic ecosystems and the potential use of Odonata as indicators of these impacts in conservation and management efforts.