Direct and indirect responses of stream and riparian organisms to experimental subsidies of Salmon

Understanding the role of resource subsidies in food webs may require a framework that explicitly considers the potential for subsidies and their effects to propagate among multiple habitats and provides a direct treatment of the mediating influences of subsidy form and temporal scale. We experimentally tested how subsidies of Pacific salmon or pelletized salmon analog influenced direct and indirect responses by organisms across multiple time scales (weeks, years) within stream-riparian habitats. Consumption of benthic insects by subsidized fishes increased by 110-140% and 44-66% in carcass and analog treatments, respectively, which directly resulted in reduced biomass of emergent adults in the riparian zone. Subsidized fishes indirectly reduced the abundance of Tetragnathidae spiders and the feeding activity of bats in riparian habitats. Our experiment demonstrated that increased productivity and predation by fishes within the stream could directly mediate patterns of emergence of aquatic insects, and in turn, have indirect effects on insectivores that share this resource. Our findings indicate that alterations to ecological processes by subsidies in one habitat can influence the sign and magnitude of ecological responses in adjacent habitats