Yeasts in the subphylum Saccharomycotina provide a powerful system for studying how ecological conditions and evolutionary history shape microbial diversity. My research combines environmental sampling, large-scale genomic resources, and trait data from hundreds of yeast species to understand how these microorganisms interact with their environments and how their metabolic abilities evolve. In this seminar, I will highlight two major themes from my work: uncovering where yeasts, including opportunistic pathogens, exist in natural habitats, and investigating why some yeast species evolve broad metabolic capabilities while others specialize on only a few resources. Together, these approaches reveal how ecological context, metabolic networks, and evolutionary processes contribute to the diversity of yeasts found across environments ranging from soils to animal hosts.