Community level niche overlap and broad scale biogeographic patterns of bee communities are driven by phylogenetic history

Aim: Because the ecological similarity between species is expected to increase with relatedness and that speciation is a local process, phylogeny may provide a common measure for the influence of ecological and biogeographic processes on community assembly. We tested if similarities in floral visitation patterns within communities and the phylogenetic beta-diversity among communities were related to the position of bees within the bee phylogeny. Location: Global. Methods: We combined a genus level phylogeny with within-genera phylogenies for the bee species occurring within 18 globally distributed bee-flower networks. Networks consisted of a matrix of bee and plant species and information on whether or not a bee species had been observed visiting flowers of a given plant species. For each network, we used Abouheif's C-mean to test if the similarity in floral associations (niche similarity) between bees and the number of plant species visited displayed a significant phylogenetic signal. To test if biogeography influenced the relatedness among species within networks we tested if the phylogenetic beta-diversity increased with geographical distance and dissimilarity in climatic conditions among networks. Results: We found a phylogenetic signal for niche similarity in only 50% of the bee-flower networks. However, network size influenced the likelihood of observing a phylogenetic signal and for seven of the eight bee-flower networks with >20 species it was statistically significant. On a global scale, the phylogenetic beta-diversity increased with geographical distances and with climatic dissimilarity between sites. Main conclusions: Bee communities are structured by processes of speciation and migration so that regional species pools are dominated by a subset of the global phylogenetic clades, resulting in increasing phylogenetic beta-diversity with geographical distance. Moreover, ecological filtering processes operating at both local (floral resource use) and continental (climatic constraints) scale determine the distribution of species among resources and geographical regions. The assembly of bee communities should therefore be understood as a product of both biogeographic and community ecological processes.