1. A large body of recent theory has recently developed focused on the relationship between the species diversity of competitor assemblages and the temporal stability of total competitor biomass. Many of these models predict that stability can increase with increasing diversity.
2. To explore natural relationships between zooplankton taxonomic diversity and temporal stability of total zooplankton biomass, 18 fishless, permanent ponds located in southern Michigan were surveyed over a 5 month period during a single growing season.
3. Results showed that temporal variability in total zooplankton biomass (measured as the coefficient of variation or CV) decreased with increasing mean zooplankton taxonomic richness. Thus, temporal stability increased with increasing taxonomic richness, consistent with theoretical predictions.
4. Decreases in the CV appeared to be because of portfolio effects (statistical averaging of species’ biomass fluctuations) rather than negative covariances among zooplankton taxa.
5. The CV of zooplankton biomass was also related to several environmental variables, suggesting that taxonomic richness may not be the only mediator of biomass stability. The CV decreased with increasing relative abundance of grazer-resistant algae (algae >35 μm in size) and the CV increased with increasing pond productivity.