. An ecogeographic analysis of the herpetofauna of the Yucatan Peninsula. Amphibians; Amphibians; Reptiles; Reptiles. 16 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY Reduction in species density at the ends of peninsulas—the so-called penin- sula effect—has been documented in Florida for amphibians and reptiles (Keister, 1971), and in Florida, Yucatan, and Baja California for birds (Mac- Arthur and Wilson, 1967), and mammals (Simpson, 1964). The phenomenon is thus a general one and is attributable to the isolating effects of peninsulas (Rick- lefs, 1973). It is of interest therefore, th
. An ecogeographic analysis of the herpetofauna of the Yucatan Peninsula. Amphibians; Amphibians; Reptiles; Reptiles. 16 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY Reduction in species density at the ends of peninsulas—the so-called penin- sula effect—has been documented in Florida for amphibians and reptiles (Keister, 1971), and in Florida, Yucatan, and Baja California for birds (Mac- Arthur and Wilson, 1967), and mammals (Simpson, 1964). The phenomenon is thus a general one and is attributable to the isolating effects of peninsulas (Rick- lefs, 1973). It is of interest therefore, that among amphibians and reptiles in the Yucatan Peninsula, only frogs exhibit this expected reduction in numbers of species. And even here something other than a peninsular effect is operating, for the reduction in numbers of species is decidedly asymmetrical (Fig. 7), a pat- tern not explainable solely on the basis of isolation. With fewest species in the middle of the peninsula, snakes and liz- ards depart even further from the ex- pected pattern. Stuart (1958) in discus- sing the herpetofauna of the Tikal- Uaxactiin area of northern El Peten, attributed the depauperization there in part to the fact that the area is transi- tional between the dry thorn forests of the outer end of the peninsula, and the wet forests of southern El Peten. Appar- ently the same situation obtains for much of northern El Peten, and southern Campeche and Quintana Roo. The con- cept of ecotone might lead one to expect more rather than fewer species in such a transitional area, but apparently this is an area which lies beyond the northern- most limits of many southern species, and beyond the southernmost limits of many northern species, especially the en- demics (Fig. 8). The factors that set these limits are discussed in the next Fig. 8.—Numbers of endemic species of am- phibians and reptiles in the Yucatan Peninsula. The figure in each square represents the num- ber of endemic specie
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