Ecology and Earth Systems research investigates the interaction of organisms, populations, and the environment. Research in this area includes studies of population dynamics, adaptation, community structure, and function, as well as the mechanisms underlying collective behavior. A special emphasis is on the area of chemical ecology, i.e., how organisms utilize small molecules to signal, sense, and interact with each other and their environment. Systems of focus range from the microbial to the metazoan at scales from microns to the Earth system. Examples of research in this area include analysis of microbial feedback on biogeochemistry, interactions of corals and fish in highly diverse communities, quorum sensing of bacterial populations, virus-host dynamics, and disease dynamics.