Effects of geographic distance and abiotic variables on larval Odonata assemblages in western Amazon savannah lakes

Odonata, comprising the suborders Anisoptera and Zygoptera, are important bioindicators of aquatic ecosystem health due to their sensitivity to environmental changes. We assessed the effects of environmental variables and geographic distance on larval Odonata assemblages in 25 natural lakes of the Brazilian savannah, in northern Roraima. We focused on Anisoptera, characterized by strong flight abilities and greater dispersal capacity, and Zygoptera, which are more sensitive to local environmental variation due to their limited dispersal capacity. We collected 9,578 larvae of 12 Anisoptera species and 2,884 larvae of eight Zygoptera species. Larval Odonata assemblages are influenced by abiotic variables rather than geographic distance, and richness was positively associated pH. Assemblage composition and abundance were affected by key abiotic conditions. Odonata abundance was positively correlated with oxygen and temperature, but negatively correlated with phosphate. Anisoptera abundance increased with dissolved oxygen and geographic distance, but decreased with phosphate and electrical conductivity. Meanwhile, Zygoptera abundance showed a positive correlation with conductivity and temperature but a negative relationship with geographic distance, pH, and phosphate. Additionally, pH influenced assemblage composition, positively affecting Anisoptera but negatively Zygoptera. Our results provide valuable insights into conservation planning and environmental policies aimed at preserving aquatic biodiversity in the region.

Key words
Aquatic insects; Anisoptera; Environmental variables; Geographical distance; Lentic; Zygoptera