Effects of biodiversity and environmental forcing on compensatory dynamics in zooplankton

Background/Question/Methods: Compensatory dynamics among competing species are an important potential mechanism for stabilizing ecosystem attributes.  The complex nature of species interactions however makes it difficult to know how prevalent such compensation is likely to be because species often show strong synchrony and because compensation may occur at some temporal scales but not others.  We examined how biodiversity and recurrent environmental forcing by nutrient additions affected the prevalence and temporal scale of compensatory dynamics in zooplankton in experimental mesocosms.  We manipulated species richness of zooplankton assemblages at 5 different levels, including one where biodiversity was enhanced by providing a weekly introduction of potential colonists from the regional metacommunity of ponds in Michigan (an ‘open’ treatment).  We cross-factored this treatment with a manipulation of nutrient additions (biweekly pulses vs constant drip). We used wavelet analysis on the Variance Ratio to quantify compensation and partition it into different time scales.

Results/Conclusions: We found that enhanced diversity led to greater compensation but that this effect was most striking for the open treatment.  We also tended to find that environmental forcing had no effect on compensation at lower levels of biodiversity but that it significantly enhanced compensation at high diversity in our ‘open’ treatments.  This effect however was only prevalent at intermediate time scales and there was no overall stabilizing effect on total zooplankton biomass because of mechanisms other than compensation.   Nevertheless our findings suggest that compensation in the face of environmental forcing may not just be a local property of the ecosystems but may also depend on their connections to a broader metacommunity of diverse organisms.