Figure 3.—

Illustration of the method of images. This represents an example of how the method of images is used to construct the various components of the coalescent process. A hypothetical rectangular habitat is outlined by a thick solid line. The two sampling locations are represented by solid stars. The rectangular habitat is repeatedly reflected across each of its boundaries to yield an infinite plane of tiled images of the original habitat. The locations of the images of one of the two original samples are indicated by the other stars. The set of images used to construct the coalescent process should include the eight images in the adjacent habitat images (shaded areas). Beyond this, the choice of exactly how many images to include is somewhat arbitrary, except that the set must include all images that are closer than the farthest included image. The circle represents the minimal radius of inclusion that incorporates the images in the eight shaded regions, determined by the distance to the farthest of these (indicated by the thick dashed line to the hatched star). Any larger radius would also represent a valid choice and would simply require consideration of additional images and correspond to a longer duration of the scattering-phase description.