New Zealand nectar microbial communities

Understanding how urbanization affects biodiversity is a key ecological goal as cities expand. While suburban gardens can be hotspots of bird, insect, and plant diversity, little is known about how host-associated microbial diversity responds to urbanization. Here we asked if communities of microbial species in floral nectar and vectored by nectar-feeding birds - thus forming a metacommunity - differed in composition and diversity between suburban and rural environments. Alternatively, we hypothesized that nectar may act as a filter, selecting for similar microbial compositions and diversity in both environments. We also asked if host identity (floral species and sugar-water feeders) predicted microbial metacommunity composition and diversity. Compared to rural birds, we found that suburban birds vectored different and more diverse microbial communities. These differences were not detected in the nectar of plant species common to suburban and rural sites for bacterial communities, which suggests that nectar filters microbial taxa and results in metacommunity convergence despite different environmental contexts. However, compared to rural bacterial beta diversity, suburban beta diversity was elevated. Bacterial taxa sorting across a more diverse pool of plant host species and sugar-water feeders drove this increase. While fungal metacommunity composition and beta diversity were similar between suburban and rural sites, alpha diversity mirrored the elevated diversity detected on birds in suburban sites. These results emphasize the interdependence of host and microbial symbiont diversity and demonstrate that human decisions, such as provisioning food for wildlife and planting diverse floral taxa, shape nectar microbial diversity in contrasting ways for bacteria and fungi. The consequences of these shifts in microbial diversity are unknown but may affect plant-pollinator interactions and plant fitness, and may spill over from urban gardens to natural plant communities.