This paper may be of some interest as it looks at populations and mobility through the lens of cooperation:
Authors: Mendeli H. Vainstein, Ana Tereza Costa Silva, Jeferson J. Arenzon
Comments: 5 pages, 6 figures, submitted to J. Theor. Biol
Subj-class: Populations and Evolution; Statistical Mechanics; Biological Physics
Abstract: We explore the minimal conditions for sustainable cooperation on a spatially distributed population of memoryless, unconditional strategies (cooperators and defectors) in presence of unbiased, non contingent mobility. We found that cooperative behavior is not only possible but may even be enhanced by such an ``always-move'' rule, when compared with the strongly viscous (``never-move'') case. In addition, mobility also increases the capability of cooperation to emerge and invade a population of defectors, what may have a fundamental role in the problem of the onset of cooperation.
Link to pdf download here
Thanks to Paul Hartzog