My research broadly addresses the question: How do global changes, including atmospheric pollution and species invasions and extinctions, change the composition and function of ecological communities? My interests range from transcontinental species invasions to interactions among microbes sharing a host. My current work focuses on how environmental changes (1) control grassland biodiversity, species interactions, and ecosystem function and (2) affect microbial communities within hosts, including (3) disease transmission and risk. I use ecological theory to guide my work, with the goal of developing a predictive understanding of these issues. Although my interests reach far beyond the grassland biome, much of my empirical work involves studying plants, insects, microbes, and disease in grasslands.