Effects of riparian arthropod predation on the biomass and abundance of aquatic insect emergence

Abstract

Adult aquatic insects are important energy subsidies for terrestrial predators, but the effects of terrestrial predators on emerged aquatic insects have been widely neglected. We compared emergence of aquatic insects from predator-free exclosures and open cages to test the hypothesis that riparian arthropod predators can reduce the abundances of emerged aquatic insects. We used emergence traps over the aquatic and terrestrial sides of the shoreline to collect insects that emerged from the water or crawled onto land to emerge. The abundances and taxonomic composition of emerged aquatic insects and riparian arthropod predators changed seasonally. Riparian arthropods consumed 45% of emerged aquatic insect biomass from terrestrial traps in spring and 45% from aquatic traps in summer. The dominant riparian predator at the time of emergence determined the specific predation effect. Stoneflies that emerged into terrestrial traps were significantly reduced when ground beetles were the most abundant predators; caddisflies that emerged into aquatic traps were significantly reduced when spiders were the most abundant predators. Thus, taxon-specific predation by riparian arthropods can affect the taxonomic composition of emerged aquatic insects.