Abstract
In increasingly urban landscapes, the loss of native pollen and nectar floral resources is impacting ecologically important pollinators. Increased urbanization has also brought about the rise of urban gardens which introduce new floral resources that may help replace those the pollinators have lost. Recently, studies have shown that the microbial communities of nectar may play an important role in plant-pollinator interactions, but these microbial communities and the floral visitors in urban environments are poorly studied. In this study we characterized the floral visitors and nectar microbial communities of Ascelpias curassavica, a non-native tropical milkweed commonly, in an urban environment. We found that the majority of the floral visitors to A. curassavica were honey bees followed closely by monarch butterflies. We also found that there were several unique visitors to each site, such as ants, wasps, solitary bees, several species of butterflies and moths, Anna’s hummingbird, and the tarantula hawk wasp. Significant differences in the nectar bacterial alpha and beta diversity were found across the urban sites, although we found no significant differences among the fungal communities. We found that the differences in the bacterial communities were more likely due to the environment and floral visitors rather than physiological differences in the plants growing at the gardens. Greater understanding of the impact of urbanization on the nectar microbiome of urban floral resources and consequently their effect on plant-pollinator relationships will help to predict how these relationships will change with urbanization, and how negative impacts can be mitigated through better management of the floral composition in urban gardens.
Highlights
The breadth and persistence of native pollinators is vital to the future of agricultural productivity, biodiversity, and ecosystem services in North America [1,2,3,4]
11 different types of insects visited the umbels at South Coast Botanic Garden (SCBG), six different types visited those at CSUF, and eight different types visited those at UCR (S2 Table)
We found that the non-metric multidimensional scaling (NMDS) showed tighter clustering of the SCBG samples and wider variance among the UCR samples similar to what we had seen when all the bacterial samples were compared (PERMANOVA F2,70 = 13.723, P < 0.001, R2 = 0.282; Fig 5A), with a slight difference in the clustering of the CSUF samples that more closely mirrored the SCBG samples
Summary
The breadth and persistence of native pollinators is vital to the future of agricultural productivity, biodiversity, and ecosystem services in North America [1,2,3,4]. The processes behind the declines in native pollinators are numerous and include global climate change [5] and habitat conversion [6]. Within the United States, the urban environment is the fastest growing land use category [7], and may act as refugia for pollinators [8,9]. Graduate Research Fellowship (NSF GRFP DGE 1656518 to MLW), and California State University Dominguez Hills. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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