This paper distinguishes between two ecological perspectives on organizational evolution: population ecology and community ecology. The perspectives adopt different levels of analysis and produce contrasting views of the characteristic mode and tempo of organizational evolution. Population ecology limits investigation to evolutionary change unfolding within established populations, emphasizing factors that homogenize organizational forms and maintain population stability. Population ecology thus fails to explain how populations originate in the first place or how evolutionary change occurs through the proliferation of heterogeneous organizational types. Community ecology overcomes these limitations: it focuses on the rise and fall of populations as basic units of evolutionary change, simultaneously explaining forces that produce homogeneity and stability within populations and heterogeneity between them.