How genotypes, populations, and species, evolve to persist, and persist to evolve

While the role of competition is well documented from community assembly to ecological speciation, it is rarely studied in ways that quantify evolutionary change or predict demographic outcomes. My thesis makes progress through combining novel experiments with classical and modern competition theory to predict ecological persistence and answer evolutionary questions. First, I experimentally demonstrate how the demographic parameters that govern competitive ability, i.e. the ability to tolerate competition, of a native grass (Vulpia microstachys) have evolved in response to the invasion of a dominant species (Bromus hordeaceus). Competitive ability reflects a complex trait–yet our understanding of how each underlying parameter evolves remains incomplete. Here I find that competitive ability is not constrained by demographic trade-offs, and find invaded populations to increase competitive ability, in part, through lower within-species competition. Second, I experimentally apply coexistence theory to uncover the mechanisms of ecological persistence among diverging lineages of an aquatic flowering plant (Spirodela polyrhiza). Although divergence is key for speciation, little is known about when allopatric lineages evolve to ecologically coexist. I find that niche differentiation rapidly accumulates to promote coexistence well before speciation (