The human body is home to a vast array of microbes. It is estimated that we have ten times more bacteria than our own human cells and that this expands our genetic repertoire by at least 100 times. Most of our associated bacteria play an important role, such as in digesting food and modulating the immune system, interacting intimately with us as well as co-occurring microbes. Recently, a number of studies have also demonstrated the importance of microbiota community dynamics on human health and disease. It is becoming evident that shifts in microbial community composition and activity can increase the susceptibility of a human host to a variety of diseases, both acute and chronic.

The key questions in this area are essentially ecological. How resistant and resilient are human-associated microbial ecosystems? What does it take to create an environment in which some members of our human microbial ecosystem take over and become harmful or in which the community becomes more susceptible to pathogen invasion?

Ecological theory and modeling can deepen our understanding of the role of human-associated microbial communities and how shifts in their composition predispose us to disease. Adaptive management can provide a means to actively monitor our microbial communities and keep them in check. While we have a good set of tools to study the spread and control of single-pathogen diseases, tools are lacking for understanding the switch between health and disease states in human-associated microbial ecosystems. By combining approaches from microbiology, community ecology and epidemiology in this symposium we seek to identify new ways to study human-associated microbial ecosystems and their impact on human health.

The proposed Symposium will provide an overview of human-associated microbial ecosystems and our current understanding of this new interdisciplinary research area. The 2009 ESA symposium "The Rainforest Within: Biodiversity of the Human Body and its Relationship to Health and Disease" was a tremendous success and we would like to use a similar format for this symposium. Each talk will be given by an ecologist or biomedical scientist who will be encouraged to maximize the accessibility of their topic to both an ecological and biomedical audience. At the end of each presentation, all speakers will be present for a panel discussion and everyone in the audience will be encouraged to actively participate.