Producer diversity enhances consumer stability in a benthic marine community
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– much less in the context of a recent invasion (i.e., Gracilaria vermiculophylla). Here we show that producer diversity, when manipulated as the only independent variable in presence of natural top-down forces, increases the stability of consumer abundance, biomass, and diversity in a benthic marine community. Using four macroalgal species, we manipulated producer diversity (i.e., identity and richness) in a substitutive design to create seven treatments. Our treatments included four monocultures, corresponding to each of the recently invasive Gracilaria and three other species (Codium fragile, Gracilaria tikvahiae, Gymnogongrus griffithsiae), two 3-species mixtures that differed only by including either the native or invasive Gracilaria in combination with Codium and Gymnogongrus, and the complete four species mixture. We followed the development of consumer communities in each treatment over 12 weeks and quantified their temporal stability.
We found that macroalgal diversity increased the stability of consumer abundance, biomass, and diversity. Macroalgal biomass did not affect any measure of stability. The invasive Gracilaria increased consumer abundance, but did not differ from the native in any other measure of functioning. Producer diversity stabilized consumer abundance by generating asynchronous temporal dynamics among different consumer populations. Our results suggest that the effects of producer diversity propagate directly upwards to maintain productivity and diversity at higher trophic levels, and thereby enhance the overall stability of food webs.