Biodiversity increases ecosystem productivity and increased productivity in one ecosystem often subsidizes adjacent ecosystems, but little is known about how biodiversity affects resource subsidy flux between ecosystems. To this end, we conducted a laboratory mesocosm experiment and comparative field study to test the influence of aquatic biodiversity on trophic subsidies from aquatic to terrestrial foodwebs using freshwater mussels as a model system. Mussels provide nutrient subsidies to stream algae, stimulating primary production. Because mussel biodiversity modifies this process, and because aquatic insect larvae track these changes in primary production, we hypothesized that mussel biodiversity would increase the production of emergent aquatic insect subsidies to terrestrial ecosystems.
Here we show that aquatic biodiversity can increase the abundance of terrestrial predators by increasing the flux of aquatic insect prey subsidies to terrestrial food webs. Mussel species richness increases the production of algae in streams through additive effects of mussel species that differ in the fertilization of algae with mussel-derived nutrients. Mussel species richness increases the emergence rates of grazing aquatic insects through non-additive effects of mussel species that differ in effects on algal community composition; as aquatic insects responded to the type, not the quantity, of algae produced. Mussel species richness increased the abundance of terrestrial spiders that tracked increases in aquatic insects. Thus, biodiversity can increase resource subsidy flux between ecosystems. Because biodiversity effects on productivity and linked ecosystems are both widespread, this suggests that biodiversity losses in one ecosystem can affect adjacent ecosystems as well.