Multicellular organisms rely upon microbial partners to metabolize food, fight off disease, and to run the machinery that sustains the air we breath, the water we drink, and soil under our feet. It would not be a stretch to say that without symbiotic microbes, multicellular life would cease to exist. While the assembly process of horizontally accumulated microbes has been a fruitful field of study, we rarely consider how non-focal habitats or hosts serve as microbial sources or sinks. In this project we assess the extent to which microbial taxa are shared across organisms and habitats within an ecosystem, and examine whether it is possible to identify reservoirs of microbial diversity where symbionts reside when outside of hosts. Here, I present data fromthe Waimea watershed, a model watershed in which a mountain ridge connects to a coral reef via 12 km of contiguous forest and a protected estuary. This short distance spans a steep gradient in elevation (~ 600 m) and a nearly 4 m rainfall differential between beach and mountaintop. Within stream, terrestrial and marine habitats we established six plots in which roughly two hundred biological samples were collected from nearly every host and substrate within or upon which microbes plausibly reside. Bacteria and fungi were enumerated using amplicon sequencing.
Results/Conclusions
We found that within plots, species richness followed a diversity gradient inversely correlated to trophic level: primary producers tended to contain the highest number of species, whereas carnivores tended to contain the fewest. Further, biological samples were significantly nested, such that microbes contained within the species-poorest samples were subsets of the diversity found in the highest richness samples. Whereas microbial communities in river, terrestrial and marine systems were compositionally distinct, there was a high degree of overlap between marine and terrestrial fungi, but not bacteria. Our work lays the important foundation for understanding potential reservoirs of microbial diversity at a landscape level. These data contribute a new dimension to our understanding of how the environment shapes host microbial composition and function.