ABSTRACT
An occupation is defined by the structure of occupations in which it takes its form and its viability depends on its ability to compete for recruits. Division of labor is here treated by analogy to speciation in mathematical ecology, using both micro and macro theories. At the level of the individual, the utilization function, the fitness set, and the adaptive function are the main analytical tools, while at the structural level it is the Lotka-Volterra equations. Viability improves by having an upper limit control on density-dependent growth, especially in a fluctuating environment. Specialist or generalist occupations occur according to the similarity of their resource use and depending on the breadth of the environment, its variability, and the grain of its spatial and temporal texture, as well as on the flexibility of the individual.
Competitive exclusion is studied in the two occupation case and generalized somewhat for more. On a resource gradient, the resulting pattern depends on responses to the environment and flexibility of the workers but, where migration occurs, geographical differentiation is less. An island of a superior occupation in a sea of an inferior may go extinct or coexist depending in immigration and competition intensities. Group selection can only occur for geographically separate groups experiencing random drift with migration between them and when individual selection is weak. A fluctuating environment affects competition by reducing the number of occupations packed on the resource continuum, by defining the degree of packing that best ensures survival of an occupation and of the community structure.
