Urbanization is one of the most pressing environmental contexts ecologists need to consider, as by 2050, nearly 70% of the world's population is projected to live in urban areas. Urbanization is generally considered a threat to biodiversity as it can have unexpected impacts. These impacts include high plant diversity in wealthy urban areas and shifts in faunal biodiversity due to the provisioning of food in urban areas. Drawing on a metacommunity framework and using naturally occurring nectar microbial communities in urban and rural settings as a model system, we addressed competing hypotheses for the drivers of local and regional diversity. Specifically, we hypothesized that while urban and rural environmental contexts may host different microbial species pools, urban contexts would host a greater variety of plant species. As previous work identified host-specific microbes, we anticipated higher alpha and beta diversity in urban compared to rural settings. Alternatively, due to the provisioning of nectar resources increasing avian abundances, we hypothesized that beta diversity may be reduced in urban setting due to increased dispersal resulting in homogenization in urban areas We tested these competing hypotheses by comparing the microbial diversity found within flowers and carried by nectar feeding birds in urban and rural sites near Auckland, New Zealand. We collected nectar and samples from nectar feeding birds in at eight urban and three rural sites during the Austral summer, and characterized the microbial communities using ITS and 16S rRNA community metabarcoding.
Results/Conclusions
We detected higher bacterial beta diversity in the urban areas and determined that this is driven by the presence additional nectar resources (plants and sugar-water feeders). However, while we anticipated an increase in beta diversity would correspond with an increase in alpha diversity, we did not detect a difference in bacterial species richness between the two environmental contexts. Curiously, fungal taxa showed the opposite trend, with higher alpha diversity present in the urban context, yet we did not detect a statistically significant difference in beta diversity between the urban and rural settings. Taken together this indicates that while overall bacterial species richness is similar between urban and rural contexts, how the microbial taxa are distributed across the nectar resources is more varied in the urban settings. While the opposite is true for the fungal taxa. As specific bacterial and fungal taxa are known to mediate plant-pollinator relationships, future work should focus on how these differences in community diversity may affect these interactions.