Studies on the importance of biodiversity for ecosystem functioning have mainly focusing on plant species diversity and direct responses such as primary productivity.  However, little attention has been given to secondary consumers and their responses to plant diversity manipulations, in part because of small spatial and temporal scales at which plant diversity has been manipulated.  Using 11 years of continuously collected data from the largest plant diversity experiment, we tested the long-term relationship between plant and consumer diversity.

Results/Conclusions

We find gross underestimation of the importance of plant diversity for associated insect diversity during the short term. There were weak, positive effects of plant diversity on insect diversity within years. Yet, higher interannual species turnover of insects in plant mixtures results in strong positive effect of plant species richness on the cumulative observed and rarefied insect richness across all years. Herbivorous insects demonstrated the strongest positive relationship with the diversity of their host plants. While observed predator richness increased with plant richness, rarefied predator diversity actually declined because predators were also more abundant in plant mixtures.  Finally, higher plant diversity dampened temporal variation in total insect abundance and the abundance of dominant herbivores, indicating plant diversity increases temporal stability of consumers.  Our results show how monitoring short term effects of diversity loss may obscure stronger community-wide effects that are most evident over longer time periods.