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3
Herpetofauna of Baja California BRADFORD D . HOLLINGSWORTH, CLARK R. MAHRDT, L. LEE GRISMER, AND ROBERT E. LOVICH
Introduction The study of the amphibians and reptiles within the state of Baja California has received consid erable attention but usually within the context of the Baja California peninsula (Van Denburgh 1895a,1895b; Schmidt 1922; Savage1960; Murphy 1983b, 1983c; Grismer 1994b , 2002; Lovichet al. 2009; Murphy and Mendez de la Cruz 2010). Here we focus on the herpetofauna within the state of Baja California, which extends from the 28th parallel to the international border with the United States, covering the northern half of the Baja California peninsula. To the south, the state shares a 142 km border with Baja California Sur, while to the north it shares a 226 Ian border with California in the United States. In the northeastern comer ofthe state, a short border is shared with Arizona (36lan) and Sonora [uz km] following the historical drainage of the Rio Colorado. The remaining boundaries are with the Pacific Ocean and Sea of Cortes and include islands in both bodies of water. Altogether, the state is approximately 70,000 km?in area. The state contains a diverse array of habitats, influenced by the extension of floral provinces from the north or the south and climatic effects from the Pacific Ocean and Sea of Cortes. The Peninsular Ranges are the dominant topographical feature of the state, running in a
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north-south orientation, with a gradual slope along the western side and an eastern face rising more abruptly, often presenting a precipitous escarpment. A series of mountains are contained within the Peninsular Ranges , with lower-elevation passes connecting regions from the west and east. Of these, the Sierra Juarez and San Pedro Martir, located in the northern half of the state, represent a major zoogeographic barrier and a high-elevation ecosystem. Two national parks cap the highest elevations of these mountain ranges, Parque Nacional Constituci6n de 1857 in the Sierra Juarez and Parque Nacional Sierra San Pedro Martir, which includes Picacho del Diablo, the highest peak (3095 m) in Baja California (Schad 1988). These mountains create a significant rain shadow effect between the relatively moist California Floristic Province along the Pacific Ocean and the Lower Colorado Desert to the east of the mountains (Shreve and Wiggins 1964; Hastings and Humphrey 1969). The Peninsular Ranges in the southern half of the state include the Sierras de La Asamblea, Las Animas, San Borja, and La Libertad. Due to their lower elevations, these mountains have less effect in isolating the surrounding ecosystems. While the Sierra LaAsamblea reaches nearly 1700 m in elevation and maintains an isolated mountaintop habitat, the southern portion of the state is dominated by the peninsular deserts
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of Baja California (Arriaga et al. 1997; Morrone 2005; Hafner and Riddle 1997), composed of th e Vizcaino an d Central Gulf Coast Desert regions (Shreve and Wiggins 1964; Wiggins 1980). As a result, transitions between the California Floristic Province an d Lower Colorado Desert in th e north and the peninsular deserts in the south are less impacted by mountain ranges and intermix gradually across wider geographic areas (Grismer 2002). A total of 119 am phibians and reptiles are found in the state of Baja California: 20 amphibians (4 salamanders, 16 frogs) and 99 reptiles (7 turtles, 51 lizards , 1amphisbaenid, 40 snakes). Six species are introduced (Xenopus laevis, Lithobates berlandieri , L. catesoeianus, Apalone spinifera, Hemidactylus turcicus, and Sauromalus varius) , and 113 are native . A total of 21species are endemic to the state . Two species are endemic to th e continental land masses (Crotaphytus grismeri and Urosaurus lahtelai), 2 are endemic to continental areas plus islands (Elgaria cedrosensis and An niella geronomensis), an d 17 are insular endemics (Elgaria nana, Crotaphytus insularis, Phyllodactylus partidus, Sauromolus hispidus, Callisaurus splendidus, Petrosaurus slevini, Uta antiqua, U. encaniad ae, U. lowei, U. tumidarosira, Aspidoscelis cana, Lampropeltis herrerae, Pituophis insulanus, Crotalus angelensis, C. caliginis, C. 10renzoensis, and C. muertensis). The herpetofauna of Baja California is broadly shar ed with the United States . Of th e 119 species found in the state, 88 (74%) also occur in the United States . AU6 of the state's m arin e species (Caretta caretta, Chelonia mydas, Eretmochelys imbricata, Lepidochelys olivacea, Dermochelys cortacea, and Hydrophis platurus) occur in coastal waters off California , and 5 of the 6 introduced species (the exception is Sauromalus varius) are also introduced into nonnative areas of the Unit ed States. The rem aining 77 species have distributions that cross the northern border of the state with California (all 77) and Arizona (38 species). Th ere are 31species of am phibians and reptiles from the state of Baja Californi a th at are en demic to Mexico, including the 21species
3
endemic to the state plus 10 that have distributions that occur entirely within Mexico. Elgaria cedrosensis, Petrosaurus repens, Phrynosoma cerroense, Sceloporus z osteromus, Aspidoscelis labialis, Bipes biporus, Arizona pacata, Hypsiglena slevini, Pituophis vertebralis, and Crotalus enyo have distributions that extend southward into the state of Baja California Sur and are confin ed to the Baja California peninsula an d its associated islands (Grismer 2002), while Sauromalus varius is an insular endemi c from Sonora and introduced to Isla Roca Lobos, Baja California (Hollingsworth et al. 1997; Hollingsworth 1998).
Previous Herpetological Studies The majority of works have focused on the faunal composition and diversity of the peninsula of Baja California , making it difficult to trac e the history of herp etological research from within the boundaries of the state. Earlier explorations mainly describ e amphibian and reptile observations from the peninsula, usually without establishin g specific locations to discern whether the observation or collected material fell within the state of Baja California or Baja California Sur. Some exceptions are collections from the establish ed port in Cabo San Lucas. For in stance, P. E. Botta made natural history collections from Cabo San Lucas while onboard the French vessel Le Heros between 1827 and 1829 (Adler 1978). This included the type specimen of Phyrnosoma coronatum described by Blainville (1835) in Reptiles de la Californie. As the Heros made its way northward along the Pacific coast, it is unlikely Botta had the opportunity to collect within the state of Baja California before the ship made port in San Diego. Earlier accounts of am phibian an d reptile observations are reviewed in Grismer (2002), which includ es details of the first written reports from the Baja California peninsula from the Jesuit missionary Clavijero in 1789. Besides a few earlier descriptions, herp etological observations were rare in the latter part of the eighteenth and first half of th e nineteenth centuries (Cris-
HER PET O FAUN A OF BA JA CALIFORN IA
m er 20 02). Following the Mexican -American War (1846-184 8) an d th e Treaty of Guadalupe Hidalgo, the boundary between th e two coun tries was revised. Dur in g this same period, the Unite d States was exploring its newly acquired territory, an d many expeditions were under way to docum ent routes into the western fronti er, includin g explorations into Baja Californ ia by the n atu ralists Spen cer F. Baird , Lyman Belding, Paul E. Botta, Townsend S. Brandegee, Walter E. Bryant , Gustav Eisen , and William M. Gabb (Grismer 2002) . An expedition to Baja California in 1867, with the consent of Mexican auth orities, was to detail the geological composition of th e peninsula an d would cross from coast to coast multiple tim es on th e journ ey northward from Cabo San Lucas to Tijuana (Dall 1909 ). As part of the expedition team, William M. Gabb (1882), while documenting the geology of the peninsula, collected th e type specim en of Phyllorhynchus decurtatus (Cope 1868, 311) in th e "upper part of Lower California ." I n the account of the expedition, Gabb consi dere d the peninsula to have three distinct districts: the Cape region, a middle section th at covered the southern half of the peninsula to as far north as Sant a Gertrudis located on th e present -day state boundary, and a north ern part above Sant a Gertrudis. Smith and Taylor (195 0 , 322) list th e restri cted type locality as "San Fernando Mision ," (between San Ignacio and) Baja California, Mexico. Here, th e location of the type specim en is not exactly clear, but it can be interpreted as meaning the no rth ern district based on Gabb's breakdown of th e peninsula. If so, P. decurtatus represents th e first species described from a specimen collected from the state of Baja Californi a (see table 3.1). The first review of the h erpetofauna of Baja California was completed by John Van Denburgh in 1895, whe n he commented that "the peninsula of Lower California lies so far from usual routes of travel tha t few collections of its anim als have foun d their way into museums." At this time, Van Denburgh (1895a, 1895b) reported on 61 species from th e peninsula, plus an addition al 7 species th e following year (Van Denb ur gh 1896).
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Twelve of these are confined to areas outside the state of Baja California. Mocquard (189 9), with help from the collections of Leon Diguet, added another 11 species to the growing knowledge of the peninsular he rpetofauna (Grismer 2002). The Bureau of Biological Survey of the United States Department of Agriculture completed an expedition of the peninsula during 190 5 and 190 6 under the direction of Edward Nelson an d assisted by Edward Goldm an . The expedition began at the US border with the assistance of Frank Steph ens of th e San Diego Society of Natu ral History. The result s, Lower California and Its Natural Resources, included accounts of am phibian and reptile discoveries, including the southe rn distribution of Crotalus cerastes (Nelson 192 2). Nelson listed 76 currently recognize d am phibians and reptiles from the peninsula, 62 of which are found in the state of Baja California. In 1911, the Albatross Expedition led by Charles H. Town send explored th e Baja California penins ula and associated islands (Townsend 1916) . Sponsored in part by the American Museum of Natural History an d the United States National Museum, th e expedition visited the islands of San Benit o, Cedros, and Angel de la Gu arda and ported in Bahia San Francisquito in th e state of Baja California. Specimens from th e expedition led to the descripti on of Cailisaurus splendulus by Dickerson (1919), in addition to numerous other species from outside th e state. The same material helped Schmidt (1922) produc e another accounting of th e h erpetofaun a of the peninsula an d associated islands and treat th e peninsula as a faun al unit (Grism er 2002). Two of th e most comprehen sive works on the reptiles and am phibians of the Baja California region appeare d in Van Denb ur gh (1922), The Reptiles of Western NorthAmerica, and later in Joseph R. Slevin (19 28), The Amphibians ofWestem North America. Much of th e material used to expand on previous works came from the 1921 Silvergate Expedition to the Sea of Cortes under the leadership of Slevin (Hann a 1922; Slevin 1922). I n addition, Van Denb ur gh an d Slevin pro duced a number of checklists and accounts describing new species from the state (Van
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2007). Islas San Benito is com posed of an archipelago of three closely positioned islands (Islas San Benito Oeste , Medio, and Este) that cover approximately 600 ha , reach 212 m in elevation, and lie 140 km off the coast (Samaniego-Herrera et al. 2007). The region is characterized as a "fog-type" temperate desert climate with little winter and summer precipitation (Meigs 1966) and is considered a part of the Peninsular Deserts (Hafner and Riddle 19 97). The. mild climatic condition is greatly influenced by pr evailing westerly winds th at move the cold California Current of the Pacific Ocean into coastal waters. The marine influence generates layers of cool, moist air that move beneath the dry, descending air, resulting in fog, low clouds, and th e lack of precipitation (Bostic 1971). Heavy fog may extend inland for 10 km (Grismer 2002 ). Maximum precipitation occurs in winter (December-February) and averages 5.5 cm . Precipitation in the spring (March-May) and summer (June-August) progressively decreases, with summer receivin g an average of 1cm of rainfall (Hastings and Turner 1965). Mean air temperatures in the summer (July-September) and winter (January-February) are between 2)"C and 28°C and 15°C and 18°C (Markham 1972), respectively, producin g a mild, temperate climate. A number of spring-fed oases, including San Fernando Velicata, Catavina, San Borja, and Santa Gertrudis, are found throughout the region, which support more mesic communities (Grismer an d McGuire 1993). In much of the region th e vegetation is open, stunted, widely spaced, an d depauperate becaus e of continuous onshore winds from th e Pacific Ocean (Grismer 2002 ). In areas protected from th e winds, plant diversity increases sharply. Th e dominant plants include blu e agave (Agave cerulata), datilillo (Yuccavalida), bursages (Ambrosia dumosa and A. camphorata), cirio (Fouquieria coiumnarisv, palo adan (F. diguetii), cardon (Pachycereus pringlei), elephant tree (Pachycormus discolor), pitahaya agria (Stenocereusgummosus), little-leaf palo verde (Cercidium microphyllum), and mes quite (Prosopis glandulosa).
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