Quantifying the contribution of double mutualists to the phylogenetic diversity of plant communities via pollination and seed dispersal

D. Matthias Dehling, Elisa Barreto Pereira and Catherine H. Graham, Swiss Federal Institute for Forest, Snow and Landscape Research, Birmensdorf, Switzerland, Elisa Barreto Pereira, Ecology, Universidade Federal de Goiás (UFG), Goiânia, Brazil

Background/Question/Methods
Animal mutualists play an important role in maintaining the diversity of plant communities via mutualistic interactions in ecological processes such as pollination and seed dispersal. In rare cases, the same animal and plant species interact in the context of two ecological processes. For individual species pairs, these so-called double mutualisms are important because they present a potential double advantage for both mutualistic partners (but also a double risk). However, the importance of double mutualism for entire plant communities is not well-known. We investigated the contribution of avian double mutualists to pollination and seed-dispersal on the Galapagos Islands, a place with a high prevalence of double mutualism. Using a new method, we quantified for each bird species the contribution to maintaining the phylogenetic diversity (PD) of the plant community by comparing the PD of the sets of plant species visited by each bird to the total PD of the plant community.
Results/Conclusions
On average, double mutualists contributed more to the phylogenetic diversity of plant species than the other mutualists, both in the context of pollination and seed-dispersal. Double mutualists with higher contributions via pollination also tended to contribute more via seed-dispersal. Our results underline the high importance of double mutualists for the diversity and functioning of plant communities.