Does the Trans-mexican Volcanic Belt represent a natural biogeographical unit? An analysis of the distributional patterns of Coleoptera

We analysed the geographical distribution of beetle species of the families Buprestidae, Cerambycidae, Dryophthoridae, Melolonthidae, Passalidae and Staphylinidae from the Trans-mexican Volcanic Belt (TVB) through a track analysis and a parsimony analysis of endemicity (PAE), in order to test its naturalness and determine its affinities. The area analysed corresponds to the TVB, which is a biogeographical province of the Mexican Transition Zone. The panbiogeographical analysis was based on the comparison of the individual tracks of 299 species of Buprestidae, Cerambycidae, Dryophthoridae, Melolonthidae, Passalidae and Staphylinidae (Coleoptera). The TVB was divided into 1o x 1o grid cells and we also included in the analysis the remaining Mexican biogeographical provinces. Parsimony analysis of endemicity with progressive character elimination (PAE-PCE) was applied to classify areas by their shared taxa according to the most parsimonious cladograms. The nested sets of areas were represented as generalized tracks. Three generalized tracks were obtained: (1) grid cells 9C, 9D, 10D, 10E, Sierra Madre Oriental, Chiapas, Mexican Gulf and the Sierra Madre del Sur; (2) grid cells 3B, 3C, 4B, 4C, 5C, 6C, 7C, Sierra Madre Occidental, Sierra Madre del Sur, Balsas Basin and the Mexican Pacific Coast, and (3) grid cells 8D, 9C, 9D, 10D, 10E, Yucatán Peninsula, Chiapas, Sierra Madre Oriental and the Mexican Gulf. We conclude that the TVB does not represent a natural biogeographical unit because it shows different relationships with other biogeographical provinces, being clearly transitional between the Nearctic and Neotropical provinces. Some parts of the TVB are related to Neotropical provinces (Chiapas, Mexican Gulf and Mexican Pacific Coast) and others to the remaining provinces of the Mexican Transition Zone (Sierra Madre Oriental, Sierra Madre del Sur, Sierra Madre Occidental and Balsas Basin).