Fitness variation across a subdivided population of the annual plant Impatiens capensis

Abstract

The evolution of a subdivided population depends on whether subpopulations with high mean fitness make a greater per capita contribution to the next generation than subpopulations with lower mean fitness. I distinguish two different models of ecological population structure, denoted local compensation and global compensation. Local compensation restricts the differential contribution of subpopulations, whereas global compensation allows subpopulations to contribute in direct proportion to their mean fitness. I describe a simple regression-based method that distinguishes these alternatives as points on a continuum of possible population structures. The method is applied to field measurements of local abundance and reproduction in a subdivided population of the annual plant Impatiens capensis. These data suggest that the global compensation model is a more accurate description of the population studied. This result is surprising because local density effects on growth and reproduction occur in I. capensis. The implications of ecological population structure for both geographical variation in selection and kin selection are discussed.