Dispersal drives the biodiversity-productivity relationship in bacterial metacommunities

Background/Question/Methods

Understanding the functional importance of biodiversity is one of the major tasks in community ecology.  Previous studies, most of which have focused on isolated communities, have shown various relationships between biodiversity and ecosystem functioning.  However, under the context of metacommunities, where local communities receive new species through dispersal, how ecosystem functioning of local communities is related to biodiversity is still unclear.  Bacteria constitute an indispensable part of the biosphere.  Recent studies challenged the traditional view of bacterial distribution, “everything is everywhere, but the environment selects”, by revealing that their dispersal is not universal.  This new finding urges more research on the influence of microorganisms’ dispersal, particularly on the relationship of their diversity and functioning. 

To address the abovementioned questions, we performed a laboratory microcosm experiment with eight bacterial species isolated from freshwater ponds.  Each of our laboratory metacommunities was composed of four aqueous microcosms, each of which was initiated with two of the bacterial species.  We manipulated the rate of weekly dispersal (control, low [0.1%] and high [1%]) among local communities, and measured the abundance of bacteria after four weeks of incubation.  We quantified bacterial productivity in local communities as their total abundance, and related it to local species richness.  

Results/Conclusions

Our results showed that bacterial productivity was positively related to species richness when there was no dispersal, and not significantly related to richness when dispersal rate was low, but negatively related to richness when dispersal rate was high.  When considering data from all dispersal treatments together, we found a unimodal relationship between bacterial diversity and productivity.  Analyses on the carbon metabolism traits suggested that the niche complementarity drove the positive biodiversity-productivity relationship in the absence of dispersal, while the negative selection effect resulted in the negative relationship under the influence of high dispersal.  

Our results highlight the importance of dispersal among local communities in determining the relationship between biodiversity and ecosystem functioning of local communities.