Departing from the population-level emphasis of density dependence research in organizational ecology, the authors examine how organizational niches within populations influence patterns of competition and mutualism. Organizational niches characterize intrapopulation variation in productive capacities and resource requirements and are operationalized for a population of day care centers (DCCs) based on the ages of children they are licensed to enroll. The authors find competitive effects of overlap density, the aggregate overlap of a DCC's organizational niche with those of all others, and mutualistic effects of nonoverlap density, the aggregate nonoverlap, which are strongest among neighboring DCCs. The authors discuss the implications of their findings for studying organizational population dynamics.