- To approximate the joint distribution of the two-colony stepping-stone model, a finite mixture approach is proposed for constructing discrete multivariate distributions. This approach generalizes the classic method of linear combinations of independent variables. The stepping-stone model is approximated through matching known moments. Numerical examples from entomology are given. Comparisons are made with the work by Wehrly et al. (1993). 1993, Taylor & Francis Group, LLC. All rights reserved.