Location of the 24 Audubon Refuges used to test the relationship between plant species diversity and the number of ELUs on each refuge.

Plant species diversity data are taken from Nichols, W., K. T. Killingbeck, and P. V. August. 1998. The influence of geomorphological heterogeneity on biodiversity: II. A landscape perspective.  Conservation Biology, 12:371-379.