Assistant Professor

Ph.D., Microbiology, Michigan State University, 1997
B.S., Biology, Humboldt State University, 1991.

Member of:
Center for Ecology and Evolutionary Biology

Laboratory Website

The diversity of life has long fascinated biologists.  Although biologists know a great deal about the diversity of plants and animals, we know very little about microbial diversity, despite the fact that microorganisms comprise most of life’s diversity. 
Research in the Bohannan group is focused on the causes and consequences of microbial biodiversity.  Recent work includes studies of the spatial scaling of bacterial biodiversity, the response of bacterial and archaeal communities to environmental change, and the role of spatial structure in the generation and maintenance of bacterial and viral diversity. 
Prof. Bohannan is especially interested in promoting the integration of microbial ecology into the general science of ecology.

Microbial biogeography

Microorganisms comprise much of Earth’s biodiversity and play critical roles in biogeochemical cycling and ecosystem functioning, yet little is known about their spatial distribution.
We are using beta-diversity analyses as a theoretical tool to answer questions about the relative importance of dispersal history and environmental heterogeneity in controllingthe spatial scaling of microbial diversity.  We are determining microbial beta diversity patterns by generating a spatially-explicit set of microbial diversity data, sampled on a global scale. These data are being generated by surveying soils in the Mediterranean-climate regions of California, Chile, South Africa, and Australia, using molecular methods for microbial community characterization. 
A variety of statistical tools are being applied to this data set in order to determine the relative importance of the different processes generating and maintaining microbial beta diversity, and how these processes vary with region, spatial scale and taxonomic resolution. 
This a collaborative project with Prof. Jessica Green of the University of Oregon.

Response of microbial communities to global change

Human activity is profoundly altering ecological systems.  These alterations include increases in atmospheric CO2 due to fossil fuel use and land use change, with subsequent changes in air temperature, precipitation and the deposition of nitrogen-containing compounds.  Recent studies have demonstrated that such multiple co-occurring global changes can alter the abundance, diversity and productivity of plant communities. 
Below ground processes – often mediated by soil microorganisms – are central to the response of these communities to global change.  However, very little is known regarding the effects of multiple global changes on microbial communities. 
We are studying the response of soil microorganisms to simultaneous increases in atmospheric CO2, precipitation, temperature and nitrogen deposition, manipulated on the ecosystem level in a grassland.  This study takes advantage of the Jasper Ridge Global Change Experiment in central California, and it is a collaborative project with Prof. Christopher Field of the Carnegie Institution of Washington and others.

Coevolution of viruses and bacteria

One of the central challenges of evolutionary ecology is to understand how coevolution organizes biodiversity over complex geographic landscapes. Most species are collections of genetically differentiated populations, and these populations have the potential to become adapted to their local environments in different ways.
The geographic mosaic theory of coevolution incorporates this idea by proposing that spatial variation in the strength of selection and gene flow across a landscape can shape local coevolutionary dynamics. Conclusive empirical tests of this theory have been particularly difficult to perform because they require knowledge of patterns of gene flow, historical population relationships and local selection pressures.
We are testing these predictions empirically using a model community of bacteria and bacteriophage (viral parasitoids of bacteria) embedded in a patchy “landscape” of chemostats linked through dispersal.  We are studying how gene flow across this spatially structured landscape alters coevolution of parasitoids and their hosts and how the resulting patterns of adaptation fluctuate in both space and time.  This is a collaborative project with Dr. Samantha Forde and Prof. John Thompson of UC Santa Cruz, and Prof. Robert Holt of the University of Florida.