Environmental and spatial determinants of aquatic and semi-aquatic Heteroptera diversity in Amazonian savanna streams

This study investigated how environmental and spatial factors structure aquatic (Nepomorpha) and semi-aquatic (Gerromorpha) Heteroptera communities in savanna streams of Marajó Island, eastern Amazon. A total of 1,038 individuals (32 species, seven families) were collected from 22 streams exposed to varying degrees of anthropogenic disturbance. Three new geographic distribution records were documented, including one for Brazil and two for the state of Pará. Habitat integrity did not significantly influence species richness, abundance, or overall community composition. In contrast, limnological variables significantly affected the composition of Nepomorpha, whereas Gerromorpha and total Heteroptera showed no such response. Variance partitioning revealed a strong influence of environmental variables, while spatial structure had no independent effect. Our findings indicate that land-use changes, such as agriculture, livestock grazing, and riparian vegetation loss, act as key environmental filters, favoring tolerant generalist species and reducing overall diversity and abundance. The predominance of apterous individuals and low oxygen concentrations reflect degraded conditions typical of disturbed savanna streams. The low sensitivity of forest-based indices in detecting degradation in savanna ecosystems highlights the need for adapted assessment tools. These results reinforce the ecological importance and vulnerability of Amazonian savanna streams, which are often neglected in conservation planning. Aquatic Heteroptera, particularly Nepomorpha, proved to be effective bioindicators of land-use impacts, underscoring the urgency of evidence-based policies to protect these fragile and increasingly threatened freshwater systems.