Contribution of emergent aquatic insects to the trophic variation of tropical birds and bats

Food webs are spatially connected by cross-ecosystem fluxes of resources, especially in aquatic-terrestrial boundaries. Generalist consumers are often supported by allochthonous resources, which can influence their density, biomass, and distribution. In this study, we investigated the influence of allochthonous aquatic resources on the foraging activity of bats (by ultrasound emissions) and richness of birds (by birdsong records). We also used stable isotope analysis of δ¹³C and δ¹⁵N to determine their diet and trophic space using bayesian Standard Ellipse Area (SEA). We evaluated these responses in near-site (0-1 m from stream margin) and far-site (200 m from stream margin) from six streams in the Atlantic and the Amazon Forest. Foraging activity of bats and richness of Amazonian birds were higher in near-sites compared to far-sites, while Atlantic bird richness was higher in far-sites. We found that emergent aquatic insects and spiders contributed to 46–45% and 49–36% of the diet of insectivorous bats and birds, respectively, regardless of the distance from streams. In Atlantic Forest, SEA of both birds and bats were not compared between plots because of the low sample size. In Amazon Forest, the far-site trophic space of birds showed a higher δ¹⁵N position in the bi-plot. These findings suggest that allochthonous resources are important for areas near and far from streams. Our study underscores the importance of preserving both near and adjacent far habitats in the maintenance of trophic interaction involving flying vertebrates and highlights the interdependence of those areas via allochthonous subsidies.