Forest Loss Influences Biomass Distribution Across Trophic Groups of Amazonian Stream Insects

ABSTRACT Changes in resource availability caused by deforestation can negatively impact freshwater ecosystems, with implications for trophic chains. We investigated both the direct and indirect effects of forest cover and allochthonous resource availability on the biomass distribution of larvae of aquatic insects (Ephemeroptera, Plecoptera, Trichoptera and Odonata, hereafter EPTO) in Amazonian streams. We hypothesized that (I) forest cover will be associated with greater availability of allochthonous resources; (II) forest cover will be associated with higher biomass of primary consumers both directly, via allochthonous inputs, and indirectly, by non‐trophic mechanisms like improved habitat conditions; (III) these patterns are strongest for shredders and collectors and (IV) primary consumer biomass positively correlated with predator biomass, results in cascading trophic effects across higher trophic positions. We sampled 135 streams across the Eastern Amazon. We used structural equation modelling (SEM) based on linear regression to assess the complex relationships among forest cover, resource availability, and biomass across different EPTO trophic groups. Our results support our hypotheses, showing patterns of association both directly and indirectly between forest cover and resource availability, primary consumers and predators. Shredder and collector biomass were higher where resource availability was high, whereas filter feeders and scrapers exhibited a weaker response. Patterns of resource limitation on predators were weaker because larger predators tend to have a broader prey spectrum that includes organisms not examined in this study. Deforestation is associated with changes in availability of allochthonous resources in streams, negatively affecting multiple trophic groups of aquatic insects through alterations in resource supply and key physical habitat features of streams. Our findings improve our understanding of the impact of human activities on aquatic biota and food chain dynamics within stream ecosystems. Our results highlight that the responses of aquatic insects to deforestation differ among functional feeding groups and trophic levels, and these responses are more strongly associated with deforestation near streams. This multiscale pattern reflects the combined influence of changes in resource availability and stream microhabitat conditions. These findings highlight the key role of riparian vegetation in managing and conserving stream ecosystems given its strong influence on resource availability and microhabitat structure in human‐modified landscapes.