Organizational ecology (also organizational demography and the population ecology of organizations) is a theoretical and empirical approach in the social sciences that is especially used in organizational studies. Organizational ecology utilizes insights from biology, economics, and sociology, and employs statistical analysis to try to understand the conditions under which organizations emerge, grow, and die.
Introduction to organizational ecology 
Introduced in 1977 by Michael T. Hannan and the late John H. Freeman in their American Journal of Sociology piece "The population ecology of organizations" and later refined in their 1989 book Organizational Ecology, organizational ecology examines the environment in which organizations compete and a process like natural selection occurs. This theory looks at the death of organizations (firm mortality), the birth of new organizations (organizational founding), as well as organizational growth and change.
Organizational ecology contains a number of more specific 'theory fragments', including:
- Inertia and change
- Niche width
- Resource partitioning
- Density dependence
- Age dependence
Organizational ecology has over the years become one of the central fields in organizational studies, and is known for its empirical, quantitative character. Ecological studies usually have a large-scale, longitudinal focus (datasets often span several decades, sometimes even centuries). The books The Demography of Corporations and Industries by Glenn Carroll and Michael Hannan (2000) and Logics of Organization Theory: Audiences, Codes, and Ecologies by Michael Hannan, Laszlo Polos, and Glenn Carroll (2007), provide the most comprehensive overview of the various theories and methods in organizational ecology.
Organizational ecology researchers include Michael T. Hannan, John H. Freeman, Glenn R. Carroll, Terry L. Amburgey, Laszlo Polos, Gabor Peli, Olav Sorenson, Jacques Delacroix, William P. Barnett, Christophe Boone, James B. Wade, Joel Baum, Henrich Greve, Heather Haveman, Alessandro Lomi, Anand Swaminathan, Giacomo Negro, Filippo Carlo Wezel, and Stanislav Dobrev.
Inertia and change 
This theory fragment holds that organizations that are reliable and accountable are those that can survive (favored by selection). A negative by-product, however, of the need for reliability and accountability is a high degree of inertia and a resistance to change. A key prediction of organizational ecology is that the process of change itself is so disruptive that it will result in an elevated rate of mortality.
Theories about inertia and change are fundamental to the research program of organizational ecology, which seeks a better understanding of the broader changes in the organizational landscape. Given the limits on firm-level adaptation, most of these broader changes thus come from the entry and selective replacement of organizations. Hence organizational ecology has spent considerable effort on understanding the founding and mortality rates of organizations.
Niche theory 
The theory fragment on niche width distinguishes broadly between two types of organizations: generalists and specialists. Specialist organizations maximize their exploitation of the environment and accept the risk of experiencing a change in that environment. On the other hand, generalist organizations accept a lower level of exploitation in return for greater security (Hannan and Freeman 1977: 948).
Niche theory shows that specialisation is generally favoured in stable or certain environments. However, the main contribution of the niche theory is probably the finding that “generalism is not always optimal in uncertain environments” (Hannan and Freeman 1977: 958). The exception is produced by environments which “place very different demands on the organization, and the duration of environmental states is short relative to the life of the organization” (Hannan and Freeman 1977: 958).
Thus, the niche theory explains variations in industrial structure in different industries. The theory shows how different structures in different industries (generalist vs specialist organizations) are shaped by relevant environments.
Density dependence 
Organizational ecology also predicts that the rates of founding and mortality are dependent on the number of organizations (density) in the market. The two central mechanisms here are legitimation (the recognition or taken-for-grantedness of that group of organizations) and competition. Legitimation generally increases (at a decreasing rate) with the number of organizations, but so does competition (at an increasing rate). The result is that legitimation processes will prevail at low numbers of organizations, while competition at high numbers.
The founding rate will therefore first increase with the number of organizations (due to an increase in legitimation) but will decrease at high numbers of organizations (due to competition). The reverse holds for mortality rates. Thus, the relationship of density to founding rates has an inverted U shape and the relationship of density to mortality rates follows a U-shaped pattern.
Age dependence 
How an organization's risk of mortality relates to the age of that organization has also been extensively examined. Here, organizational ecologists have found a number of patterns:
- Liability of newness. Here, the risk of failure is high initially but declines as the organization ages.
- Liability of adolescence. The risk of mortality will be low at first as the organization is buffered from failure due to support by external constituents and initial endowments. But when these initial resources become depleted, the mortality hazard shoots up and then declines following the liability of newness pattern.
- Liabilities of aging. Here, the risk of failure increases with organizational age. This could be due to a liability of senescence (internal inefficiences arising from the aging of the organization) or a liability of obsolescence (a growing external mismatch with the environment).
Evolutionary approaches to organizations 
Organizational ecology can be usefully compared with evolutionary theories in economics (e.g. Nelson & Winter, 1982). Main similarities between these strands of literature are: (1) the emphasis on organizational routines and the limits to organizational adaptibility, (2) the population or system level of analysis and (3) the importance of environmental selection. Organizational ecology's perspective is more Darwinistic (see Hannan & Freeman, 1989, pp 20–22), while Nelson & Winter (1982, p. 11) provide a more Lamarckian perspective. Another important difference concerns the question what is selected by the environment: "organizational forms", as in organizational ecology, or "routines" as in the evolutionary economics literature? Authors like Joel Baum and Arjen van Witteloostuijn have argued for the potential of cross-fertilization between these two research strands. Stauber 2013
See also 
- Biocultural evolution
- Organizational behavior
- Organizational Behavior Management
- Organizational studies
- Douma, Sytse and Hein Schreuder, 2013. "Economic Approaches to Organizations". 5th edition. London: Pearson  ISBN 0273735292 • ISBN 9780273735298
- *Douma, Sytse and Hein Schreuder, 2013. "Economic Approaches to Organizations". 5th edition. London: Pearson  ISBN 0273735292 • ISBN 9780273735298
Baum, J.A.C., S.D. Dobrev and A. Van Witteloostuijn (eds, 2006), "Ecology and Strategy." Amsterdam: Elsevier
Carroll, G.R. and M.T. Hannan (2000) The Demography of Corporations and Industries. Princeton, NJ: Princeton University Press.
Carroll, G.R. (1985) “Concentration and specialization: dynamics of niche width in populations of organizations.” American Journal of Sociology 90 (6): 1262-83.
Hannan, M.T. and J. Freeman (1977) “The population ecology of organizations.” American Journal of Sociology 82 (5): 929-964.
Hannan, M.T. and J. Freeman (1989) Organizational Ecology. Cambridge, MA: Harvard University Press.
Hannan, M.T., L. Polos, and G R. Carroll (2007) Logics of Organization Theory: Audiences, Code, and Ecologies. Princeton: Princeton University Press.