Gulf of California xeric scrub
The Gulf of California xeric scrub ecoregion is situated along the eastern coastal zone and Gulf of California versant of the Baja Peninsula in Mexico, and is delineated by the spine of the La Giganta Sierra Mountains. This ecoregion, located entirely within the nation of Mexico, is classified within the Deserts and Xeric Scrublands biome. Species richness of plants is high in the ecoregion, but modest for fauna; however, endemism is high in this arid habitat, which receives some of the lowest precipitation in all of Mexico.
There are a total of 341 vertebrate species present in the ecoregion. Twenty genera of plants, nine species of the herpetofauna, twelve species of mammal, and two species of avifauna are endemic to this region. Reptilian endemism is particularly notable, with some lizard taxa of highly restricted occurrence on certain small islands in the Gulf of California within this ecoregion. Although much of this xeric scrub remains intact, cattle overgrazing and urban development have destroyed extensive areas of the natural environment.
Location and general depiction
This region is delineated by its most prominent feature, the mountain range of Sierra of La Giganta. La Giganta aligns north-south along the eastern portion of the Baja California peninsula. Igneous (piroclastic, basaltic, and andesitic lava) and sedimentary rocks from the tertiary make up the region. Its altitudes vary between 200 to 1000 metres (m), and in some localized portions elevations exceed 1000 m. To the west of the ecoregion is the Gulf of California.
The climate is arid hot in the narrow coastal plains on the east of the Baja Peninsula, but it becomes arid semi-hot as the distance from the coastal zone increases. Precipitation reaches some of the lowest levels of all Mexico (<100 millimeters per annum). Temperature oscillations are extreme.
Dominant flora species are Creosote Bush (Larrea tridentata) and White Bursage (Ambrosia dumosa); moreover, other plant taxa occurring here include: Arizona Nettle-spurge (Jatropha cinerea), Desert Ironwood (Olneya tesota), Acacia brandegeana, Blue Palo Verde (Cercidium floridum), and Chloroleucon mangense var. leucospermum. Species of more mesic habitats occur on the many oases that are present on the Baja Peninsula: Mexican Fan Palm (Washingtonia robusta), Southern Cattail (Typha domingensis), Common Reed (Phragmites australis) and Date Palm (Phoenix dactylifera). The oases are remnants of more extensive mesic environments that existed in the peninsula in prehistoric times; these earlier habitats consisted of larger bodies of surface water distributed throughout the peninsula, surrounded by vegetation that belongs to wetlands interspersed with common elements of the xeric scrub.
The Gulf of California xeric scrub represents one of the largest well-preserved extensions of arid lands in Mexico. It is home to many endemic and endangered species. The isolation of the Baja California Peninsula from other deserts and from the continent is in part responsible for the high levels of endemism and diversity of organisms in this region: 238 species of plants, 32 reptiles and amphibians, 199 birds (two endemic), and 64 mammals (twelve endemic). There are twenty endemic genera of plants, and 20 to 25 percent of the plant taxa are endemic; nine species of the herpetofauna are endemic and ten are exclusive to the ecoregion's oases; 37 of the birds are migrants that derive from the USA and Canada. The xeric scrub of Baja California houses the oldest tree of any desert: the Palo Fierro or Desert Ironwood (Olneya tesota). Over 160 plant species depend upon legumes such as Desert Ironwood and Screwbean Mesquite (Prosopis pubescens) for their regeneration in arid lands, as well as endangered wildlife species such as the Desert Bighorn Sheep (Ovis canadensis nelsoni) and Masked Bobwhite Quail (Colinus virginianus ridgwayi), that use the Desert Ironwood tree both as shelter and as a forage resource. Desert Ironwood tree nursing relationships promote diversification and increase richness of other plants in arid ecosystems.
Unlike its continental counterpart ecoregion, the Sonoran Desert, biodiversity in the Gulf of California xeric scrub occurs chiefly in various oases that remain in this arid region. Oases represent a relict of the ancestral vegetation that once dominated Baja California; they serve as refuges for endangered and endemic species or for those species that were extirpated from less dry environments in the peninsula. They also serve as resting areas for migrant birds that resume migration after foraging on the rich sources of food that oases provide. Arid lands are characterized by high number of endemic taxa; despite their apparent aridity, these ecosystems are highly valuable for conservation in terms of the biological uniqueness of supported organisms. There are numerous special status taxa that are found in the Gulf of California xeric scrub ecoregion, denoted variously as Near Threatened (NT), Vulnerable (VU), Endangered (EN), Critically Endangered (CR), or Extinct (EX).
Only two anuran taxa are found in the Gulf of California xeric scrub ecoregion: Red-spotted Toad (Anaxyrus punctatus); and the Pacific Treefrog (Pseudacris regilla).
The Isla Santa Catalina Leaf-toed Gecko (Phyllodactylus bugastrolepis) is an endemic reptile to the Gulf of California xeric scrub, occurring only on Isla Santa Catalina, and often found in dead cacti. Other reptile species found here include: the endemic Santa Catalina Island Whiptail (Cnemidophorus catalinensis), seen only on Santa Catalina Island in the Gulf of California; the endemic Santa Catalina Island Spiny Lizard (Sceloporus lineatulus); the endemic San Lorenzo Islands Lizard (Uta antiqua); the endemic Salsipuedes Island Whiptail (Cnemidophorus canus), restricted in occurrence to endemic to the islands of Salsipuedes, San Lorenzo Norte and San Lorenzo Sur ; the endemic Raza Island Leaf-toed Gecko (Phyllodactylus tinklei), found on Raza Island; the endemic Santa Cruz Leaf-toed Gecko (Phyllodactylus santacruzensis); the endemic Isla Partida Del Norte Leaf-toed Gecko (Phyllodactylus partidus), found solely on Isla Partida Norte and Cardonosa Este, in the Gulf of California; the endemic Angel Island Leaf-toed Gecko (Phyllodactylus angelensis), found only on several Gulf of California islands in the county of Islas Angel de la Guarda; the endemic Las Animas Island Gecko (Phyllodactylus apricus); and the near-endemic Marbled Whiptail (Cnemidophorus marmoratus), the latter of which occupies burrows in sandy soils.
Special status reptiles found in the ecoregion include the endemic Santa Catalina Island Rattlesnake (Crotalus catalinensis CR), whose chief prey is the Slevin's Deer Mouse (Peromyscus slevini CR), which species is also restricted to Santa Catalina Island. Other special status reptiles in the ecoregion are: the San Lucan Leaf-toed Gecko (Phyllodactylus unctus NT) and the endemic Isla San Pedro Mártir Side-blotched Lizard (Uta palmeri VU), restricted solely to Isla San Pedro Martir, Sonora. Other reptilian species occurring in the ecoregion include: the Cape Arboreal Spiny Lizard (Sceloporus licki); and the Five-toed Worm Lizard (Bipes biporus).
There are a number of mammalian taxa present in the Gulf of California xeric scrub, including: Angel Island Mouse (Peromyscus guardia CR), an ecoregion endemic known only from Ángel de la Guarda Island in the northern Gulf of California, México; the ecoregion endemic Burt's Deermouse (Peromyscus caniceps CR), known only from Montserrat Island, Baja California Sur, Mexico; Baja California Rock Squirrel (Spermophilus atricapillus EN), a Baja California endemic; and the Fish-eating Bat (Myotis vivesi VU), which is found along in the coastal zone of Baja California and Sonora. Bunker's Woodrat (Neotoma bunkeri EX) was previously endemic to the ecoregion and is now extinct.
The Gulf of California xeric scrub remains partially intact, despite intensive human activity in and around the area. Large portions of habitat are well preserved, but the system is considered fragile and in high risk of perturbation due to cattle overgrazing, human population growth, agricultural fires, and over-extraction of water from the oases. This ecoregion is encoded by the designation NA1306 by the World Wildlife Fund.
Ecological threat profile
Grazing of domestic cattle has effectively displaced populations of pronghorn, mule deer, and mountain sheep, and hunting of the Puma (Felis concolor) has been a common practice among native villagers; both phenomena have reduced the populations of the aforementioned mammals. Habitat destruction for agriculture and human settlement threatens the xeric scrub and its many endemic cacti; as a consequence, the introduction of animal and plant species could displace native fauna and flora through direct competition. Tourism activities in the region have become extensive, enhancing the dangers of pollution and other disturbing effects on the flora. The introduction of Buffel-grass (Cenchrus ciliaris) to feed cattle has been especially detrimental, because that grass accumulates combustible litter that causes the complete burning of Desert Ironwood and other native plants.
As arid grasslands replace the xeric scrub, the recruitment of perennials may be lower or completely non-existent; if this practice remains uncontrolled, the landscape of the region could change dramatically. Populations of the Peninsular Yellowthroat (Geothlypis beldingi) have already been extirpated from some of the oases due to human population pressure on the habitat. A reserve has been advanced to protect the ecoregion. Management plans for the area are needed, since wildfires and logging by native peoples threaten the habitat; moreover, and human exploitation of resources and irregular human settlements are growing at a quick pace.
- S. Alvarez, P. Galina, y L. Grismer. 1997. Anfibios y reptiles. Pages 125-142 in L. Arriaga, y R. Rodríguez-Estrella (editors). Los Oasis de la Península de Baja California. México: CIBNOR. ISBN: 8449414180
- L. Arriaga, S. Díaz, R. Domínguez, y J. L. León. 1997. Composición florística y vegetación. Pages 69-106 in L. Arriaga, y R. Rodríguez-Estrella (editors). Los Oasis de la Península de Baja California. México: CIBNOR.
- Búrquez, A., y M. A. Quintana. 1994. Islands of diversity: Ironwood ecology and the richness of perennials in a Sonoran Desert biological reserve.
- CONABIO Workshop, 17-16 September, 1996. Informe de Resultados del Taller de Ecoregionalización para la Conservación de México.
- CONABIO Workshop, Mexico, D.F., November 1997. Ecological and Biogeographical Regionalization of Mexico.
- I. Ferrusquía-Villafranca. 1993. Geología de México: Una Sinopsis. Mexico: Instituto de Biología, UNAM.
- C. Michael Hogan, ed. 2013. Phyllodactylus angelensis; Phyllodactylus bugastrolepis; Phyllodactylus tinklei. Encyclopedia of Life.
- Jiménez, M.L., C. Palacios, y A. Tejas. 1997. Los Macroartrópodos. Pages 107-124 in L. Arriaga, y R. Rodríguez-Estrella (editors). Los Oasis de la Península de Baja California. México: CIBNOR.
- Y. Maya, R. Coria, y R. Domínguez. 1997. Caracterización de los Oasis. Pages 5-26 in L. Arriaga and R. Rodríguez-Estrella (editors). Los Oasis de la Península de Baja California. Mexico: CIBNOR.
- R. Rodríguez-Estrella, L. Rubio, y E. Pineda. 1997. Los oasis como parches atractivos para las aves terrestres residentes e invernantes. Pages 157-196 in L. Arriaga, y R. Rodríguez-Estrella (editors). Los Oasis de la Península de Baja California. México: CIBNOR.
- J. Rzedowski. 1978. Vegetación de Mexico. Editorial Limusa. Mexico, D.F., Mexico. ISBN: 9681800028
- SEMARNAP. 1996. Programa de áreas naturales protegidas de México, 1995-2000.
- J. Tewksbury y C. A. Petrovich. 1994. The influences of ironwood as a habitat modifier species: A case study on the Sonoran Desert coast of the Sea of Cortez.
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