127gradient and define the centers of distribution for features or branches. These features
are assumed to have a uniform distribution of range-extents along the gradient
(Faith and Walker 1996a). Graphically, the height to the top of the gray area above
any demand point (Fig. 4a) reflects the number of features centered at that point that
are not overlapped by any of the selected sites; these would be features having a
Fig. 3 ED analyses for the ordination space based on PD-dissimilarities, from Rintala et al.
(Fig. 2 ). Black dots are samples as in Fig. 2 and two of the samples are labelled, x and y. Hollow
dots are ED demand points. A small number of demand points, uniformly covering the range of
samples in the space, are used here to illustrate the method. (a) Ordination space showing samples
and demand points. (b) Line segments connect each demand point to its nearest sample, among all
samples in a defined subset. The ED value is the sum of these distances. Here the subset includes
all samples. (c) Sample site x is lost from the subset, and ED is re-calculated based on the new line
segments. (d) Sample site y is lost and ED is re-calculated based on the new line segments
Using Phylogenetic Dissimilarities Among Sites for Biodiversity Assessments...