Producer diversity enhances consumer stability in a benthic marine community

Summary The diversity of many communities is changing due to local extinctions and invasions. Understanding the consequences of these changes is vital to their successful conservation, yet few studies have experimentally investigated how producer diversity affects the stability of higher trophic levels. Here, we show that producer diversity, when manipulated as the only independent variable in the presence of natural top-down forces, increases the stability of consumer abundance, biomass and diversity in a benthic marine community. Using four macroalgal species (Codium fragile, Gracilaria tikvahiae, Gracilaria vermiculophylla and Gymnogongrus griffithsiae), we manipulated producer diversity (identity and richness) in a substitutive design to create seven treatments. Our treatments included four monocultures, two 3-species mixtures that differed only by including either the native or invasive Gracilaria and the complete four-species mixture. We followed the week-to-week dynamics of producer and consumer communities in each treatment concurrently for 12 weeks and quantified their temporal stability. We found that higher producer diversity increased the stability of a diverse, productive consumer community. Producer biomass production did not affect consumer production or diversity, suggesting that producer diversity was solely responsible for driving the mechanisms underlying the observed multitrophic diversity–stability relationships. Taken together, our results indicate that higher producer diversity directly increased consumer diversity by increasing overyielding and decreasing the temporal variance of this response variable and that this increased consumer diversity enhanced consumer stability via increased asynchrony among consumers. Synthesis. Our results suggest that the effects of producer diversity propagate upwards to maintain diversity and productivity at higher trophic levels, and thereby enhance the overall stability of food webs.