Population ecology of organizations is a recent research perspective on how ecological dynamics interact with organizational growth in the evolution of organizational populations. This approach focuses on the relationships between changes in social structures and changes in populations of organizations. Thus it is especially well-suited for developing connections between theory and research on organizations and broad macrosociological concerns. The full dynamics of populations of organizations involve vital rates (of founding and mortality) as well as growth and decline of individual organizations. However, in the interest of analyzing data on diverse populations over long periods, recent research in organizational ecology has emphasized vital rates and has slighted issues of growth and contraction at the organizational level. The present research seeks to redress the balance by building models of organizational ecologies in which individual organizations grow and contract. That is, it explores the implications of adding growth at the organizational level to models of organizational ecology. Incorporating growth into existing population-ecology models encounters two kinds of complications. The first concerns the absence of appropriate data. Existing data sets do not provide time-paths of fluctuations in sizes of organizations in complete populations, which are needed to estimate growth models. Efforts to estimate models of growth using only data for large organizations, for which records on size can often be found, face serious problems of sample-selection bias. The second difficulty concerns the complexity of models that incorporate microdynamics into ecological models. Given the present state of knowledge, there is no serious prospect for analytic characterizations of the dynamics of organizational populations. Although we have begun to understand various aspects of the dynamics, we do not yet know how to integrate these aspects analytically. Given the paucity of appropriate empirical data and the analytic complexity of the problem, this research will rely on a combination of microsimulation and empirical analyis. Microsimulation will be the main tool for learning about the effects of various growth mechanisms and ecological constraints for the evolution of organizational populations. The proposed empirical analyses use sequences of size distributions on selected populations in order to learn whether the models developed in the simulations fit empirical situations. In particular, these analyses will explore whether the models can explain observed change over time in sequences of empirical cross-sectional distributions. The findings of the research will (1) demonstrate whether ecological processes are sensitive to assumptions about processes of growth and decline at the organizational level, and (2) show how size distributions affect processes of competition and legitimation within organizational populations.
