We examined the effects of competition for food resources from nonnative honey bees (Apis mellifera L.) and nonnative alfalfa leafcutting bees [Megachile rotundata (F.)] on native alkali bees (Nomia melanderi Cockerell) with different ratios of the pollinators. In commercial alfalfa, Medicago sativa L. (=lucerne) seed fields, we studied the contribution of competition from nonnative bees on the decline of alkali bees as commercial pollinators. Bees were counted in an estimated square meter of blooming alfalfa during alkali bee flight. We conclude that contest competition or nonaggressive physical displacement of alkali bees by honey bees occurs, and that exploitative competition or resource displacement of alkali bees by alfalfa leafcutting bees occurs. The implications of competition and displacement of alkali bees in their role as commercial pollinators are discussed. We also use the alkali bee model for discussing the potential effects of introductions of nonnative bees into the United States on native bees.