An ecogeographic analysis of the herpetofauna of the Sierra San Pedro MaÌ�rtir region, Baja California, with a contribution to the biogeography of the Baja California herpetofauna

3H PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES Vol. 46, No. 1, pp. 1-72, 21 figs., 6 tables. December 7, 1988 AN ECOGEOGRAPHIC ANALYSIS OF THE HERPETOFAUNA OF THE SIERRA SAN PEDRO MARTIR REGION, BAJA CALIFORNIA, WITH A CONTRIBUTION TO THE BIOGEOGRAPHY OF THE BAJA CALIFORNIA HERPETOFAUNA Hartwell H. Welsh, Jr. ' Pacific Southwest Forest and Range Experiment Station, Forest Service, U^,/]/ U.S. Department of Agriculture, 1700 Bayview Drive, Areata, California 9552 V Abstract: An ecogeographic analysis of the distributions of the herpetofauna of the Sierra San Pedro Martir Region of Baja California was undertaken. The Martir Region is part of northern Baja California from approximately latitude 30°N to 31°N. Over 3,000 locality records from the literature, museums, and field work were analyzed across a matrix of ecogeographic formations based on regional climates, physiography, and extant vegetation. Numerical and heuristic methods of biogeographic analysis indicated the 65 species present occur in seven distinct patterns. Examination of these contemporary patterns within and beyond the Martir Region led to a hypothesis of five historical patterns of evolutionary development among the Baja California herpetofauna. This hypothesis indicates that vicariance, dispersal (diffusion), and in situ evolution are interacting phenomena contributing to contemporary herpetofauna! distributions in peninsular and insular Baja California and the Pacific Southwest. Received Sept. 30, 1987. Accepted March 21, 1988. Introduction There is a growing consensus that ecological factors limit the geographic range of all organ-isms (e.g., Udvardy 1 969; MacArthur 1 972). Ro-tramel (1973:229) expressed it thusly: ". . . bio-geographic areas originate from and are maintained by the interactions of organisms with physical and biotic factors in their environ-ments." He noted a lack of placing proper em-phasis on ecological factors in biogeographic analysis, which he attributed to historical influ-' Formerly with the U.S. Fish and Wildlife Service, National Ecology Center, Dept. oflnterior, 1300 Blue Spruce Drive, Ft. Collins, Colorado 80524. ences, and concluded that ". . . continued pro-gress in solving the questions of the origins of biogeographic areas will require biogeographers to clearly distinguish the origins of species from the origins of areas and then develop new meth-ods of eco-geographic analysis" (Rotramel 1 973: 230). The ecogeographic characteristics of a species' distribution can be viewed as the present sum-mation of the continuous evolutionary process of interaction and compromise that occurs be-tween that species and its environment. A new adaptation to the environment that promotes greater survivorship of offspring within an area, or population expansion into new areas, is a new characteristic of the ecological strategy of that