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The Oases of Central Baja California, Mexico. Part I. A Preliminary Account of the Relict Mesophilic Herpetofauna and the Status of the Oases





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A preliminary account of the relict mesophilic herpetofauna of the oases of central Baja California supports previous hypotheses of an historical ecological transformation of central Baja California from a mesic to a xeric region. The general herpetological pattern that emerges is that a treefrog (Hyla cadaverina and/or H. regilla), a slider turtle (Trachemys scripta), and the two-striped garter snake (Thamnophis hammondii) usually occur in a particular oasis. Occasionally, other mesophilic lizards and snakes are found, as well. The hypothesis we present is that these mesophilic taxa had a continuous transpeninsular distribution during earlier wetter periods, but with the rapid desertification of central Baja California in the last 8000-10,000 years, these species have become restricted to the mesic refugia of oases in the central peninsular portion of their ranges. Unfortunately, many of the oases are being severely altered by direct and indirect human activities which, in some cases, have persisted for nearly 300 years since the Mission Period. Physical alterations include damming for irrigation, pumping for drinking water, and trampling by cattle. Biological alteration includes the introduction of non- native species of plants and animals. Such alterations have led to the extinction and/or decline of some of the mesophilic herpetofauna in some of the oases.