Species and interactions are being lost at alarming rates and it is imperative to understand how communities assemble if we are to prevent their collapse and restore lost interactions. Using an eight-year dataset comprising nearly 20,000 pollinator visitation records, we explore the assembly of plant-pollinator communities at native plant restorations sites in an agricultural landscape. We find that species occupy highly dynamic network positions through time, causing the assembly process to be punctuated by major network reorganizations. The most abundant and generalized pollinator species are also the most variable in their network positions and interaction partners, contrary to what preferential attachment --- the most widely studied theory of ecological network assembly --- predicts. We suggest assembly instead occurs via an opportunistic attachment process. Our results contribute to our understanding of how communities assemble and how species interactions change through time while helping to inform efforts to re-assemble robust communities through restoration.