Computer models will be upgraded to include newly acquired information on mortality and longevity. Confined populations will continue to be monitored with emphasis on social organization and levels of aggression. These data will be pursued through behavioral observations and manipulation of populations. Specifically, studies on all female and one male populations will be completed and all male and four female popultions will be started. In addition, we plan to examine the effects of environmental and density cues to reinitiate reproduction. A population of M. musculus will be permitted to attain maximum density and reproductive shutdown. The entire population will be transferred to an identical cage with clean bedding. In a second series, subordinates will be harvested by groups of ten. If reinitiation of population growth does not occur, then we will consider harvesting dominant animals. Also, the factors involved in reproductive shutdown at high density will be examined in animals singly caged as well as in populations. The degree of influence of anestrus, pseudopregnancy, post-implantational blocks, resorption and abortion will be weighed against the dynamics and phases of population growth. Neurological and hormonal pathways of reproductive and maturational inhibition will continue and be expanded to include hypothalamic and pineal involvement.