There is recent abundant literature describing the geographical patterns of species distribution at different spatial scales. Most of these descriptions analyze the data through richness, and sometimes beta diversity plots in birds and mammals, without relating explicitly alpha and beta diversity. A new technique, the richness-range plot allows displaying simultaneously richness and distributional range size of a group of species
Results/Conclusions
In this work we used high resolution (~1km2) distribution maps to analyze the alpha (local richness) and beta (the ratio of regional species richness to mean local richness) diversities patterns of the Mexican vertebrates at two spatial scales (~4km2 and 256km2). We combine these results through using richness-range. The observed patterns were compared to different null models (with a different degree of the PAM randomization). All the groups present a latitudinal pattern of higher species richness towards the equator, although they vary in details, with major transitions in the Transmexican Volcanic Belt and the Sierras Madre Oriental y Occidental. Beta diversity determines the position of a cloud of points in the richness-range plot. In low beta-diversity groups like birds, in general, there is a higher proportion of species in each cell compared to the proportions of the other groups. At the larger cell size, it is possible to find up to 60% of the resident birds in a single 250 km2 cell, while it is not possible to find more than 20% of the amphibians or reptiles species due to their smaller distributional ranges in average, showing more restriction than in mammals or birds (i.e. a higher beta value in such two groups). We also comment the implications for conservation of these findings.
