Halffter's Mexican Transition Zone, beetle generalized tracks, and geographical homology

Aim Halffter's Mexican Transition Zone is a complex area in which the Neotropical and Nearctic regions overlap. We test its existence and extension through a track analysis of beetle taxa, and discuss the implications of geographical homology. Location The area analysed corresponds to the Caribbean subregion, which occupies Mexico, Central America, north-western South America, and the Western Indies. Methods The panbiogeographic or track analysis was based in the comparison of 134 individual tracks belonging to different beetle taxa (species and supraspecific groups). A Parsimony Analysis of Endemicity (PAE) was applied in order to classify the areas by their shared taxa according to the most parsimonious cladogram, and the nested sets of areas were represented as generalized tracks. Results Two generalized tracks resulted: (1) northern generalized track: comprising the Sierra Madre Occidental, Sierra Madre Oriental, Transmexican Volcanic Belt, Balsas Basin and Sierra Madre del Sur biogeographic provinces; and (2) southern generalized track: comprising the Chiapas, Mexican Gulf, Mexican Pacific Coast and western Panamanian Isthmus biogeographic provinces. Main conclusions The generalized tracks obtained correspond broadly to Halffter's Nearctic and Mesoamerican patterns, respectively; however, in contrast to Halffter's Mesoamerican pattern, the southern generalized track extends further north through the lowlands of the Pacific and Mexican Gulf coasts.