Amphibians and Reptiles of Baja California, Including Its Pacific Islands and the Islands in the Sea of Cortes / Edition 1

Amphibians and Reptiles of Baja California, Including Its Pacific Islands and the Islands in the Sea of Cortes / Edition 1

ISBN-10:
0520224175
ISBN-13:
9780520224179
Pub. Date:
09/16/2002
Publisher:
University of California Press

Hardcover

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Overview

Amphibians and Reptiles of Baja California, Including Its Pacific Islands and the Islands in the Sea of Cortes / Edition 1

The Baja California peninsula is home to many forms of life found nowhere else on earth. This, combined with the peninsula's rugged and inaccessible terrain, has made the area one of the last true biological frontiers of North America. L. Lee Grismer is not only the foremost authority on the amphibians and reptiles of Baja California, but also an outstanding photographer. He has produced the most comprehensive work on the herpetofauna of the peninsula and its islands ever published. With its stunning color images, detailed accounts of many little-known species, and descriptions of the region's diverse environment, this is the definitive guide to the amphibians and reptiles of a fascinating and remote region.

The culmination of Grismer's quarter century of fieldwork on the Baja peninsula and his exploration of more than one hundred of its islands in the Pacific Ocean and the Sea of Cortés, this book gives information on the identification, distribution, natural history, and taxonomy of each species of amphibian and reptile found there. Preliminary accounts of the life history of many of the salamanders, frogs, toads, turtles, lizards, and snakes are reported here for the first time, and several species that were almost unknown to science are illustrated in full color. The book also contains new data on species distribution and on the effect of the isolated landscape of the peninsula and its islands on the evolutionary process.

Much of the information gathered here is presented in biogeographical overviews that consider the extremely varied environments of Baja California in both a contemporary and a historical framework. An original and important contribution to science, this book will generate further research for years to come as it becomes a benchmark reference for both professionals and amateurs.

Product Details

ISBN-13: 9780520224179
Publisher: University of California Press
Publication date: 09/16/2002
Series: Organisms and Environments Series
Pages: 413
Product dimensions: 8.50(w) x 11.00(h) x 1.45(d)

About the Author

L. Lee Grismer is Professor of Biology at La Sierra University.

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Amphibians and Reptiles of Baja California, Including Its Pacific Islands and the Islands in the Sea of Cortés

Organisms and Environments, 4
By L. Lee Grismer

University of California

Copyright © 2002 Regents of the University of California
All right reserved.

ISBN: 0-520-22417-5


Chapter One

GENERAL INTRODUCTION

Baja California is the second longest and the most geographically isolated peninsula in the world. Over the last four to five million years, it has undergone a uniquely complex tectonic origin and ecological transformation. What we see today as the Baja California peninsula was originally connected to the west coast of mainland Mexico but was torn away by differential movements of the Pacific and North American plates. Since then, it has been carried approximately three hundred kilometers to the northwest along what has become known as the San Andreas Fault. This separation occurred in various stages of uplift, submergence, and geographical fragmentation. Concurrent with these tectonic upheavals were climatic changes that transformed the peninsula from a generally cool and more mesic region to one of extreme aridity. This change was gradual at first but has rapidly accelerated over the last eight to ten thousand years.

Because of its latitudinal extent, its complex topography, and its location between two very dissimilar bodies of water, Baja California accommodates a wide range of climates. This range in turn supports a striking degree of environmental diversity, with habitats ranging from the extremely hot and arid Lower Colorado Valley Desert in the northeast to the humid, tropical deciduous forests of the south. Additionally, a thick coniferous forest is found in its northern mountains and an endemic pine-oak woodland in the Sierra la Laguna of the Cape Region. Central Baja California is covered with an extensive network of volcanic badlands interrupted by palm-lined oases, and its north-central region is one of only three fog deserts in the world. Yet despite its ecological diversity and unique environmental history, Baja California remains one of the most poorly studied regions in North America.

Exploration and Research

Exploration and research in Baja California have not yet enjoyed the same attention or success as investigations in the United States or mainland Mexico. This is not a situation that has developed by chance alone but rather one that has emerged through design. Baja California, on the whole, is extremely arid and rugged. The vast majority of its interior is accessible only by foot or on horseback, and thus a researcher's field time is limited by the amount of fresh water and other supplies that can be carried. The scarcity of permanent sources of fresh water in central Baja California has allowed development only in isolated regions near oases or semipermanent riparian areas in the mountainous regions. Even today, simply traveling from one rancho to the next often requires a moderate degree of isolation and travel through unforgiving terrain.

The logistic difficulties impeding research were made clear in two prominent episodes of Middle American exploration that resulted in a noticeable lack of publications dealing with Baja California's natural history. The first involved the series Biología Centrali-Americana-a 67-volume compilation dedicated to the advancement of knowledge of the flora and fauna of Mexico and Central America. This publication, which spanned the period from 1879 to 1915, expressly excluded Baja California. The second period encompassed the Hobart M. Smith and Edward H. Taylor expeditions in Mexico, during which nearly fifty thousand specimens of amphibians and reptiles were collected between 1932 and 1941. Although this effort culminated in the publication of three major annotated checklists by Smith and Taylor (an unparalleled advancement in our knowledge of Mexico's herpetofauna), not a single specimen was collected from Baja California. And still, in spite of the information presented in this book, a gap remains in our knowledge of the herpetofauna of Baja California and the Gulf of California (the Sea of Cortés). Virtually no detailed ecological or natural history studies have been conducted on any species in Baja California, and there is uncertainty as to the exact distribution of others. The harshness and isolation of the islands in the Gulf of California have dissuaded detailed ecological studies on all but a few species. Additionally, many isolated areas such as the Vizcaíno Peninsula, the Sierra los Cucapás, and the upper elevations of the Sierra la Asamblea, Sierra San Borja, Sierra la Libertad, Sierra Guadalupe, and Sierra la Giganta probably contain species that have not been reported and unknown species that have yet to be described. Baja California and the Sea of Cortés are long overdue for a comprehensive treatment of their herpetofauna.

The Environment

A thorough understanding of any faunal element requires a sound knowledge of the historical and contemporary ecology of the region in which it occurs. This is especially true of the herpetofauna of Baja California. Unlike continental regions, Baja California has undergone complex tectonic and ecological transformations as a result of uplift, submergence, isolation, and desertification, and these transformations have contributed to its environmental diversity. Thus an understanding of the dynamic relationships and interactions among these abiotic components, both past and present, is paramount in understanding the relationships, distribution, and geographic variation of its herpetofauna.

Paleoenvironmental History

FORMATION OF THE BAJA CALIFORNIA PENINSULA

The most significant factor contributing to the endemism and the biotic diversity seen today in Baja California and the Sea of Cortés is the complex geological origin and evolution of these regions. Between 8 and 13 million years ago (mya), most of Baja California lay submerged beneath the Pacific Ocean and nestled against the northwest coast of mainland Mexico, placing what is today the city of San Felipe against the west coast of Isla Tiburón and placing Cabo San Lucas just north of Puerto Vallarta, Jalisco (Gastil et al. 1983). A shallow epicontinental seaway, the proto-Gulf of California, inundated western Mexico, extending north to at least Isla Tiburón and perhaps into southern California by 6 mya (Stock and Hodges 1989; Winker and Kidwell 1986). With the onset of several complex tectonic events associated with differential movements between the Pacific and North American plates, along what would eventually develop into the San Andreas Fault, Baja California was being torn away from the west coast of Mexico and began to migrate northwest (Lonsdale 1989). At the same time, the peninsular ranges were being uplifted, and depositional filling began forming the Vizcaíno Desert and the Magdalena Plain. During its migration, Baja California underwent many changes in contour and topography. Parts of the peninsula may have been influenced by marine inundations, giving it the appearance of an archipelago, while other portions were giving rise to mountain ranges and were besieged with volcanic activity. For a short period, the Cape Region became separated from the rest of the peninsula and existed as an island, while the Gulf of California remained in the Coachella Valley of southern California at least as far north as Whitewater Canyon in Riverside County (Winker and Kidwell 1986). In fact, it may have been the recent uplift of coastal mountains in southern California that contributed to the Gulf's final regression to its present location.

Overlaid on the geomorphological and physiographic evolution of the Baja California peninsula was a series of climatic changes. These changes were the result of an overall drying trend in North America, which actually began during the Eocene-before the peninsula began to separate from mainland Mexico. The intermittent glacial periods of the Pleistocene and the formidable rainshadows caused by the uplift of the Peninsular Ranges brought severe localized drying trends to Baja California that persist today. In the past, however, the central portion of Baja California was a cool, mesic, volcanic, wooded grassland whose upper elevations supported large stands of oaks and other trees much like those seen today in some portions of the Sierra Madre Occidental of Sonora, Mexico. Horses and giant tortoises ranged through these forests. The Cape Region of Baja California was tropical and supported populations of crocodiles, green iguanas, and boa constrictors, as well as semiaquatic elephants, giant hares, and large cats (Miller 1980). Eventually Baja California became the long, topographically complex, generally arid peninsula that we recognize today. This is not to say that its dynamic past has become dormant. To the contrary, the continued tectonic activity along the San Andreas Fault and its associated fault systems attest to the peninsula's unrest and continued northwestward movement.

It has been this intricate evolution of Baja California's physiography, coupled with its complex historical ecological transformation and currently diverse climatic regimes, that has resulted in organisms becoming isolated in particular regions at various points in time and permitted their invasions and reinvasions into other areas during other periods (Grismer 1994a,b). The overall effect of these events has been the evolution of unique flora and fauna and distinct biotic provinces. We must keep in mind, however, that we are merely observing the evolution of Baja California and its inhabitants at a particular moment (the present). Just as conditions and organisms have changed and evolved in the past, they will continue to do so in the future.

FORMATION OF ISLANDS

The islands associated with Baja California vary in age, origin, and geological composition. In the Sea of Cortés, there are three principal types of islands, defined by the manner of their origin: oceanic, continental, and landbridge. Oceanic islands have never been connected to mainland Mexico or to Baja California but originated in the Sea of Cortés. Their origin may be due to uplift, as a result of extensional rotation or compression of the underlying tectonic plates, or to volcanic deposition from a series of underwater eruptions. Both are phenomena associated with the crustal extension and the northwesterly movement of the peninsula as it continues to drift away from mainland Mexico. Isla Tortuga, off the coast of Santa Rosalía, is an example of an oceanic island formed by volcanic deposition.

Continental islands were once connected to mainland Mexico or the Baja California peninsula but became separated as a result of tectonic displacements along coastal fault zones. In the Gulf of California, these are usually islands that broke off the trailing edge of the peninsula as it moved northwest. An example is Isla Ángel de la Guarda.

By far the most common type of island in the Sea of Cortés, and along all of Baja California's Pacific coast (with the exception of the Islas San Benito), is the landbridge island. Landbridge islands are relatively young islands (no more than fifteen thousand years old) that were once connected to the mainland or the peninsula. Many of them are simply the emergent peaks of nearby coastal ranges. For the most part, these peaks became isolated because of a rise in sea level. Occasionally landbridge islands are formed from coastal submergence where the earth's crust is thinned as it is stretched. This thinning causes the ground to sink and water to enter from a nearby sea. Such an event may have been the first step in the formation of the proto-Gulf of California. Some landbridge islands have been formed by erosion, which can cut off prominent points of coastal areas and leave them isolated. Isla Espíritu Santo, off the coast of La Paz, may have been created by coastal erosion. There are a few other landbridge islands-such as Isla Willard, which forms part of the northern end of Bahía San Luis Gonzaga, and Isla Requesón, in Bahía Concepción-that are connected to the peninsula by a sandy isthmus at low tide but separated at high tide.

Physical Characteristics

An in-depth knowledge of the physiography (shapes and contours) of Baja California is a prerequisite for understanding the geographical orientation of its various phytogeographic regions. Because the distribution of many species is correlated with phytogeography, understanding the physiographic nature of Baja California is essential to comprehending why much of the herpetofauna occurs where it does. Additionally, this knowledge provides insight into the various climatic regimes of Baja California, which reciprocally dictate the distribution of the phytogeographic regions. Thus, physiographic insight is fundamental to understanding the geographical interactions between the herpetofauna and the environment. Major geographic features and towns mentioned below are shown in map 1.

Today Baja California is a thin northwest to southeast-tending peninsula nearly 1,300 km long. It is situated between 32° 30{pr} N latitude and 117° W longitude at its northwestern corner and 23° N and 110° W at its southern tip. Its width ranges from approximately 240 km along the U.S.-Mexican border to less than 30 km at the Isthmus of La Paz. It is separated from the state of Sonora by the Río Colorado in the north and from the rest of Sonora and mainland Mexico by the Gulf of California, approximately 160 km wide. The area of Baja California is approximately 143,400 km², and its coastline is approximately 3,300 km long. Associated with the coastline are forty-five major islands, each at least 1.3 km² in area. Several smaller islands are also associated with Baja California, and an additional ten or so major islands are principally associated with the Mexican states of Sonora and Sinaloa (maps 2 and 3).

The most distinctive feature of Baja California's dramatically sculpted topography is a series of mountain ranges, known collectively as the Peninsular Ranges, that run nearly uninterrupted from its northern border to the Isthmus of La Paz. This massive fault-block system is tilted westward toward the Pacific Ocean, and its crest lies slightly to the east of the peninsula's central axis. On the west side the mountains slope gradually toward the coast, whereas the eastern face rises abruptly out of the desert floor, often presenting a precipitous escarpment. Many passes and minor depressions have been cut into the main crest of the Peninsular Ranges, and other, minor fault systems have given rise to additional ranges that radiate outward from the main massif at various angles. The result is a rugged and complex topography that allows the Peninsular Ranges to be conveniently divided into a series of less extensive ranges.

Dominating northern Baja California are two major mountain ranges known as the Sierra Juárez and the Sierra San Pedro Mártir. The Sierra Juárez, which reaches an elevation of nearly 1,410 m, is part of a mountain range that extends from southern California.

(Continues...)


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Table of Contents

Foreword, by Harry W. Greene
Preface
Acknowledgments
General introduction
1. Salamanders
2. Frogs and Toads
3. Turtles and Tortoises
4. Lizards
5. Worm Lizards
6. Snakes
Appendix A.
Insular Species Checklist
Appendix B. Claves taxonómicas
Glossary
Literature Cited

Index

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