Spatial scale and β-diversity of terrestrial vertebrates in Mexico

Patterns of diversity are scale dependent and beta-diversity is not the exception. Mexico is megadiverse due to its high beta diversity, but little is known if it is scale-dependent and/or taxonomic-dependent. We explored these questions based on the self-similarity hypothesis of beta-diversity across spatial scales. Using geographic distribution ranges of 2 513 species, we compared the beta-diversity patterns of 4 groups of terrestrial vertebrates, across 7 spatial scales (from similar to 10 km(2) to 160 000 km(2)), within 5 different (historically and environmentally) regions in Mexico: Northwest, Northeast, Centre, Southeast and the Yucatan Peninsula. We found that beta-diversity: 1) was not self-similar along the range of scales, being larger than expected according to the null model at coarse scale, and lower, but not significantly different, to expected at intermediate and fine scales; 2) varied across spatial scales, depending on the taxonomic group and on the region; 3) was higher at coarser scales; 4) was highest in the Centre and Southeast regions, and lowest in the Yucatan Peninsula, and 5) was higher for amphibians and reptiles than mammals and birds. As a consequence, beta-diversity of each group contributes differentially to the megadiversity of Mexico, likely due to a variation in the biogeographical histories and the perception of each group to environmental heterogeneity. These results show the importance of identify the appropriate geographical scale for biodiversity conservation analyses, such as for example, the analysis of complementarity.