Methods for comparison of biotic regionalizations: the case of pteridophytes in the Iberian Peninsula

We made several regionalizations of the Iberian Peninsula based on the distributions of the pteridophyte flora to see whether the regionalization depended on the type and scale of lattice or the similarity index considered. We used five types of lattice in which the scale also varied: river basins, mountains and plains, natural regions, physiographic and geological regions, and administrative provinces; and two similarity indices: those of Jaccard and of Baroni-Urbani and Buser. The regionalizations varied according to the type of lattice, the grain size, and the similarity index used. To assess the different regionalizations we used four methods: 1) the coefficient of variation of the size of sites in each lattice. 2) the bestblock method, which considers as the hest lattice that which maximizes the number of matches between presences over all pairwise site comparisons. 3) the Mantel test, to assess the statistical significance of the regionalizations obtained, and 4) mapability, which considers the most contiguous regionalization to be the best. The best regionalization according to our four criteria was that based on administrative provinces and Jaccard's index. This yielded a small central region and three large regions: northern, western, and eastern.