. An ecogeographic analysis of the herpetofauna of the Yucatan Peninsula . Fig. 22.—The Yucatan-East Mexico pattern of distribution. Extra-peninsular distributions are rough approximations. tus), subspecies pairs (, Terrapene mexicana ijucatana and T. m. mexicana), and populations showing little or no dif- ferentiation (, Hyla ehraccata). Par- simony requires the assumption that the common ancestor of each pair inhabited an environment similar to that presently occupied by its descendants. Therefore, we may infer that disjunct populations inhabiting similar habitats betoken a more wide
. An ecogeographic analysis of the herpetofauna of the Yucatan Peninsula . Fig. 22.—The Yucatan-East Mexico pattern of distribution. Extra-peninsular distributions are rough approximations. tus), subspecies pairs (, Terrapene mexicana ijucatana and T. m. mexicana), and populations showing little or no dif- ferentiation (, Hyla ehraccata). Par- simony requires the assumption that the common ancestor of each pair inhabited an environment similar to that presently occupied by its descendants. Therefore, we may infer that disjunct populations inhabiting similar habitats betoken a more widespread and continuous distri- bution of that habitat at some time in the past. We need to know what histor- ical events were responsible for effecting the breakup of these habitats. I believe that two sets of events—Pleistocene changes in climate and vegetation, and pre-CoIombian human influences—have been of overriding importance in shap- ing these patterns of distribution. Pleistocene Changes in Climate AND Vegetation The conventional view of the tropics in general, and the Neotropics in partic- ular, as ancient and stable environments must be abandoned in the light of the paleobotanical and paleoclimatological evidence that has been accumulating steadily, especially during the past 15 years. Griscom (1942) was one of the first to advance this view when he sug- gested that Pleistocene climate changes resulting in the expansion and contrac- tion of vegetation zones were important in shaping patterns of bird distribution in Central America. His idea that the montane forests of Central America were sufficiently lowered to completely pinch out the lowland rainforest is probably incorrect. However, it now seems certair.
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