When can plant-pollinator interactions promote plant diversity?

In the light of rapid losses of biodiversity worldwide, it has become more important than ever to study the factors that ensure the continued existence of diverse ecological communities. Whereas the diversity-enhancing effects of antagonistic interactions are relatively well understood, much less is known about the contribution of mutualistic interactions to biodiversity maintenance. This study assesses the influence of mutualistic interactions with pollinators on the diversity of plant communities with alternative means of reproduction besides animal pollination. In contrast to a recent more general model of plant-animal mutualisms, the results of our simulations suggest that interactions with pollinators do not generally promote plant diversity, irrespective of the structure of the interaction network. Despite a potential for increased plant species richness through the positive effect of pollinators on plant birth rates, species richness was mostly negatively affected by the presence of pollinators because existing abundance asymmetries were amplified by animal pollination. Our results imply that for plant communities with alternative means of reproduction, the loss of pollinators will usually not lead to decreased diversity. However, whereas the immediate effects of pollinator loss on plant community composition may be negligible, the long-term population genetic consequences are likely to be severe.