In this study, the interactions among populations and the effects on founding rates are examined within the context of organizational ecology theory. Two populations, bank intermediary institutions and non-bank intermediary institutions, which perform the same activities in the financial market in Turkey, are selected. Each population’s density, the amount of their financial activities and the different time periods are taken as independent variables and the effects of these variables on founding rates are tested empirically. The results show that the population of bank intermediary institutions has a dominant effect on the population of non-bank intermediary institutions.