Zooplankton species richness-productivity relationship: Confronting monotonic positive and hump-shaped models from a local perspective

This study examined two models that are most frequently used to describe the relationship between species richness and productivity (SPR): monotonic positive and hump-shaped models. We assessed zooplankton community diversity in response to algal productivity. The relationship between net primary productivity (NPP) and rarefied species richness was examined by fitting the data to two models and comparing them using the Akaike information criterion (AICc). Macrophyte banks with the highest net primary productivity had the highest zooplankton abundance. Our results pointed to a hump-shaped model as the best fit to describe the relationship between zooplankton species richness and primary productivity (ΔAICc>4). Thus, the diversity was lower at the extremes of productivity and higher at intermediate levels of productivity. We suggest that this relationship might occur because when the resource supply rates are low, environmental conditions are stressful, whereas a high availability of resources enhances competitive exclusion. Two observations supported this statement: (i) the total abundance of the community positively correlated with NPP (P<0.05), indicating that less productive sites had few consumers and the raised productivity tended to favour the total abundance; (ii) NPP was negatively correlated with evenness (P<0.05), indicating that productivity increased the dominance of certain species in the communities. Therefore, we challenged two of the models most frequently used to explain SPR, and discuss some mechanisms underlying a hump-shaped SPR. © 2013 Ecological Society of Australia.