Figure 1.—

Habitat geometry and boundary conditions. The two-dimensional habitat considered in this article is a rectangle of dimensions L₁ × L₂, where L₁ ≥ L₂. Two different treatments of the boundaries are considered. In the “rectangular” model, reflecting boundary conditions are assumed, and a lineage exiting the habitat reenters on the same side. In the “toroidal” model, periodic boundary conditions are assumed, and a lineage reaching the boundary reenters the habitat from the opposite side.