Abstract
Global biodiversity losses provide an immediate impetus to elucidate the relationships between biodiversity, productivity and stability. In this study, we quantified the effects of species richness and species combination on the productivity and stability of phytoplankton communities subject to predation by a single rotifer species. We also tested one mechanism of the insurance hypothesis: whether large, slow-growing, potentially-defended cells would compensate for the loss of small, fast-growing, poorly-defended cells after predation. There were significant effects of species richness and species combination on the productivity, relative yield, and stability of phytoplankton cultures, but the relative importance of species richness and combination varied with the response variables. Species combination drove patterns of productivity, whereas species richness was more important for stability. Polycultures containing the most productive single species, Dunaliella, were consistently the most productive. Yet, the most species rich cultures were the most stable, having low temporal variability in measures of biomass. Polycultures recovered from short-term negative grazing effects, but this recovery was not due to the compensation of large, slow-growing cells for the loss of small, fast-growing cells. Instead, polyculture recovery was the result of reduced rotifer grazing rates and persisting small species within the polycultures. Therefore, although an insurance effect in polycultures was found, this effect was indirect and unrelated to grazing tolerance. We hypothesize that diverse phytoplankton assemblages interfered with efficient rotifer grazing and that this “interference effect” facilitated the recovery of the most productive species, Dunaliella. In summary, we demonstrate that both species composition and species richness are important in driving patterns of productivity and stability, respectively, and that stability in biodiverse communities can result from an alteration in consumer functioning. Our findings underscore the importance of predator-prey dynamics in determining the relationships between biodiversity, productivity and stability in producer communities.
Highlights
With unprecedented species extinction rates [1,2,3] and concomitant changes in ecosystem functioning [4,5,6] worldwide, there is a need to understand the relationships between biodiversity, productivity and stability at different trophic levels
We used a diverse pool of taxa to quantify the effects of species combination and richness on productivity and response variable O2 production biovolume
Species combination was most important to productivity whereas species richness was most important to stability (Table 3)
Summary
With unprecedented species extinction rates [1,2,3] and concomitant changes in ecosystem functioning [4,5,6] worldwide, there is a need to understand the relationships between biodiversity, productivity and stability at different trophic levels. One mechanism that has been proposed to explain positive biodiversity-productivity relationships is niche partitioning, whereby species with different morphological or physiological characteristics can use different resources increasing overall productivity in species rich systems [13,14,15,16] Extending this concept from productivity to stability, a functionally diverse group of taxa may be more resistant or resilient to environmental or biological perturbations because different species exhibit different tolerances and responses to changes in environmental and biological factors. We test compensatory dynamics explicitly by creating phytoplankton polycultures with species that are likely to differ in their ability to resist predation With this design, we show that algal polycultures are more productive and stable than algal monocultures, due to indirect predator-mediated effects. This finding highlights the importance of predator-prey dynamics in understanding the role of biodiversity in producer communities
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