A biogeographic analysis of the herpetofauna of northwestern Nuclear Central America

Typescript (photocopy).Two-hundred eighty-nine species of native terrestrial herpetofauna are known to occur within the boundaries of northwestern Nuclear Central America, the Mexican land mass east of the Isthmus of Tehuantepec, exclusive of the Yucatan Peninsula. The area is extremely variable with respect to major environmental parameters. The distribution of each herpetofaunal species is discussed relative to seven physiographic regions, 10 vegetation formations, and elevation. The herpetofauna are not restricted to particular physiographic regions or vegetation formations, but most species can be identified as occurring within distinct faunal areas that are regulated by climate, topography, and elevation. Distributional groups of herpetofauna are identified and classified as either belonging to 13 recognizable geographic assemblages or to three groups not conforming to distinct faunal areas; species within each group are listed. Assemblages are composed of species showing continuous or disjunct geographical ranges. Analysis of the herpetofauna of northwestern Nuclear Central America reveals that neither the study area nor Nuclear Central America is composed of a homogeneous assemblage of reptiles and amphibians, but contain species that are primarily restricted to the Mesoamerican region. However, highland areas of Nuclear Central America contain enough endemic species to justify a Nuclear Central American subregion of Mesoamerica. Sixty-two species enter the Nearctic or Neotropical regions, and most of those are considered as having a Mesoamerican origin. Only 22 species are regarded as having a Nearctic or Neotropical origin, with a slight majority being Nearctic forms. Patterns of geographic distribution of the herpetofauna of northwestern Nuclear Central America are used to substantiate or refute thoughts concerning historical reasons for modern biotic distributions. Both vicariance and dispersal theory are used to explain the formation of modern distributional patterns of the herpetofauna. Vicariance events were primarily responsible for affecting pre-Pleistocene source biotas, and Pleistocene climatic fluctuations caused separation of disjunct assemblages described herein