Effects of fish species richness on organism export from aquatic to terrestrial habitats

The effects of losses in aquatic species richness may cascade to terrestrial ecosystems through emergence of organisms with complex life-histories, such as insects and amphibians. I tested the effect of predatory fish species richness on aquatic insect emergence and tadpole abundance using large outdoor stream mesocosms. In a substitutable design, I manipulated richness (0, 1, 2 or 3 species) of three predatory fish species with different foraging strategies: benthic (Etheostoma spectabile), water-column (Cyprinella lutrensis), and surface (Gambusia affinis). I tested fish species interactions for risk-enhancement, risk-reduction, or substitutability. Preliminary results suggest fish reduced emergence of a dragonfly species (Pantala flavescens), but had no effect on total emergent insect biomass, abundance, or trophic structure. Fish drastically reduced tadpole abundance within mesocosms, presumably reducing frog emergence (not measured). Tests for fish interactions largely showed substitutability, with some species combinations showing risk-enhancement, but never risk-reduction. This research generally supports recent theory suggesting that multiple predators with non-overlapping microhabitats should have redundant effects on prey with broad habitat domains. Additionally, this research suggests that changes in predatory fish species richness may alter energy export from aquatic systems, but effects are limited to a small subset of available prey.