Mechanisms of pollinator diversity effects on pollination in experimental plant communities

Background/Question/Methods

It is generally assumed that biodiversity is important for ecosystem functioning, a paradigm of increasing relevance in the face of global environmental change threatening biodiversity. However, studies about diversity effects in pollination are extremely scarce, although it is an important ecosystem process and threatened by pollinator declines. We set up an experiment with 14 different flowering plant species in 56 flight cages of eight square meters. Different communities of one to five wild bee species were established in these cages in addition to some control treatments. Thereby, we are able to test the biodiversity-functioning relationship for pollinator diversity for the first time in a realistic scenario, controlling for abundance and environmental effects.

Results/Conclusions

Our study showed a general trend for a positive effect of pollinator diversity on pollination success of a plant community including diverse plant families and flower types. Focusing on the underlying mechanisms revealed that functional complementarity with respect to weather conditions and flower preferences explained the pollination effect of bee communities much better than did the number of species. Plant-pollinator interaction networks were strongly influenced by interactions among bee species further accentuating the effect of realized complementarity in multispecies communities: more plant species were visited by multi-species bee communities because bees shifted to alternative flowers in the presence of other species, a mechanism never shown in previous biodiversity experiments. We conclude that biodiversity-ecosystem functioning relationships are important in pollination systems, but knowledge on biological traits and mechanisms strongly improves the ability to predict pollination value of different bee communities.