Responses of Odonata assemblages to habitat integrity and environmental variation in Amazonian streams: lessons for conservation

Rapid landscape transformation in the Amazon, driven by human activities such as deforestation and intensive land use, has deeply affected the aquatic ecosystems, especially small forest streams (i.e., igarapés). These environments rely heavily on riparian vegetation to maintain the physical and chemical conditions that support biodiversity. Among aquatic insects, the order Odonata are particularly sensitive to habitat alteration and are therefore frequently used as bioindicators. Here, we evaluated how habitat integrity and local environmental conditions were associated with richness, abundance and species composition of adult Odonata species in igarapés of the Eastern Amazon. We expected igarapés with higher habitat integrity and lower levels of human disturbance to harbor higher Zygoptera richness, whereas Anisoptera would be relatively more represented in lower-integrity igarapés. We sampled 30 igarapés along a gradient of environmental alteration. We found that better-preserved igarapés harbored higher Zygoptera diversity, whereas more degraded environments were dominated by tolerant Anisoptera, as predicted. However, Anisoptera richness was not significantly higher in igarapés with lower habitat integrity, although their relative abundance was higher in such habitats. In addition, limnological variables, such as electrical conductivity and coarse particulate detritus, played central roles in structuring communities. These results demonstrate that adult Odonata provide complementary information on environmental change that may not be detected through total richness and abundance alone and reinforce their use as effective tools for environmental assessment, monitoring, and conservation planning in Amazonian igarapés. Implications for insect conservation Our results show that declining igarapés habitat integrity can alter Odonata assemblage composition by favoring disturbance-tolerant species and reducing the representation of environmentally sensitive taxa. These changes may occur without a corresponding decline in total species richness, highlighting the importance of incorporating suborder- and species-level responses into biomonitoring programs. Maintaining riparian vegetation, organic-matter inputs, and favorable water-quality conditions is therefore essential for conserving Odonata diversity in Amazonian igarapés.