Tamaulipan mezquital
The Tamaulipan mezquital is a deserts and xeric shrublands ecoregion in the southern United States and northeastern Mexico. It covers an area of, encompassing a portion of the Gulf Coastal Plain in southern Texas, northern Tamaulipas, northeastern Coahuila, and part of Nuevo León.
Distribution
The Sierra Madre Oriental range to the west separates the Tamaulipan mezquital from the drier Chihuahuan Desert. The Tamaulipan matorral is a transitional ecoregion between the mezquital and the Sierra Madre Oriental pine-oak forests to the west and the Veracruz moist forests to the south. The Western Gulf coastal grasslands, known as the Tamaulipan pastizal south of the border, fringe the Gulf of Mexico. The Edwards Plateau savannas lie to the north, and the East Central Texas forests and Texas blackland prairies to the northeast.Geography
Hydrology: The region is generally semi-arid however, various wetlands are present. The Laguna Madre is one of only five hypersaline coastal lagoons in the world and a significant ecosystem in itself, laying between the Gulf of Mexico and the Tamaulipan mezquital ecoregion. As one moves inland from the hypersaline lagoon, a relatively narrow band of freshwater marshlands are encountered running north to south, albeit occurring fragmented and irregularly. These marshes are dynamic, fluctuating with rainfall and tropical storm activity, and alternating with wet and dry periods. When and where present, these marshlands can be locally, surprisingly extensive with deep marshes and both permanent and ephemeral freshwater ponds that support populations of salamanders, turtles, and millions of migrating waterfowl, such as redheads in the winter.Several rivers cross the region, all flowing eastward to the Gulf of Mexico. Many of these river have created innumerable oxbow lakes, resacas, and abandoned channels with associated marshes and swamps as they meander across the coastal plain. The few remaining riparian zones in this region that have not been cleared for agriculture, housing, and industry, can support unexpectedly lush tropical jungle vegetation, particularly in the south. The San Antonio River runs at the approximate northeastern border of this region. Other major rivers include: the Nueces River and its tributary the Frio River; Rio Grande and its tributaries Rio Salado, Rio San Juan ; the Rio San Fernando ; the Rio Soto La Marina and its tributaries Rio San Carlos, Rio Pilón, San Antonio, Rio Purificacion, Rio Corona, Rio Santa Ana, form the approximate southern border.
A number of large lakes occur in the region, but they were all constructed in the decades fallowing the Second World War in the 20th century. These include: Choke Canyon Reservoir and Lake Corpus Christi in the Nueces River drainage in the USA; Amistad International Reservoir and Falcon International Reservoir on the Rio Grande; Presa Venustiano Carranza in Coahuila on the Rio Salado, Presa El Cuchillo in Nuevo Leon and Presa Marte R. Gómez in Tamaulipas on the Rio San Juan, and Presa Vicente Guerrero in Tamaulipas on the Rio Soto La Marina drainage in Mexico.
Flora
Mezquital is characterized by honey mesquite and curly mesquite grass. Prior to disturbance, the most common shrubs were probably lotebush and whitebrush.Parts of this region consisted of open woods of mesquite, with a pronounced understory of grasses. The grasses in this community contained a layer of taller species such as hooded windmill grass and fourflower trichloris, and a layer of shorter species such as grama. In some places dense stands of Texas prickly pear occurred instead of shrubs and grasses.
Brushy species include huisache, blackbrush and other acacias, desert hackberry or granjeno, cenizo, whitebrush, Texas prickly pear, and tasajillo.
Mexican palmettos and Montezuma cypresses grow in riparian zones, such as along the Rio Grande.
Cacti: This region is rich in cacti diversity. A few species found in the province include: root cactus, triangle or barbed wire cactus, star cactus, Berlandier's hedgehog, pitaya, Allicoche hedgehog cactus, ladyfinger hedgehog, Dahlia cactus, Junior Tom Thumb cactus, Turk's head barrel cactus, peyote, Heyder's pincushion cactus, hair-covered cactus or Texas pincushion, pale mammillaria, twisted rib cactus and several others.
Fauna
Mammals: This region once hosted an impressive number of carnivores but, most were very rare, or entirely extirpated by the early to mid 20th century. The gray wolf is extirpated and black bears are now largely restricted to the Sierra de Picachos in Nuevo Leon, Mexico. The most recent records of the jaguar in Texas, USA are from the early 1950s, but the species still lingers, although at risk of extinction in Mexico. Similarly, jaguarondi, ocelot, and margay are all threatened or endangered in the USA and Mexico. Some puma or mountian lion, White-nosed coati, and American Badger populations still persist, apparently in stable numbers in some remote areas, although the latter is considered a threatened species in Mexico. A few other species such as the Northern Raccoon, Coyote, and to a lesser extent Bobcats have adapted to human encroachment and development.Other mammals found in the region include the collared peccary, white-tailed deer, black-tailed jackrabbit, nine-banded armadillo, Mexican long-tongued bat, and the southern yellow bat. Rodents include the predatory northern grasshopper mouse, the Mexican prairie dog, spotted ground squirrels and others such as Coue's rice rat, southern plains woodrat, Mexican spiny pocket mouse, and Merriam's pocket mouse.
Birds: The southern part of the ecoregion is an Endemic Bird Area and is home to the red-crowned amazon, tawny-collared nightjar, Tamaulipas crow, long-billed thrasher, Altamira yellowthroat, crimson-collared grosbeak. Other species occurring in this region include the white-tailed hawk, plain chachalaca, green parakeet, buff-bellied hummingbird, Couch's kingbird, and Audubon's oriole as well as wide ranging tropical species such as the green jay, least grebe, Ferruginous pygmy owl, ringed kingfisher, and the great kiskadee.
Reptiles: The American alligator reaches the southwestern limit of its distribution in the north of this region and the Morelet’s crocodile reaches the northwestern limit of its distribution in the south. Likewise, the red-eared slider occurs in the north and the closely related Mesoamerican slider in the south. Other turtles such as the Mexican box turtle, Rio Grande cooter, spiny softshell, and the yellow mud turtle occur there. The geographic distribution of the Texas tortoise nearly matches that of the Tamaulipan mezquital ecoregion.
The Laredo striped whiptail is a species complex of all female lizards that reproduce by parthenogenesis that is endemic to this region. The reticulate collared lizard is also endemic. Other representative lizards include the Texas banded gecko, four-lined skink, common spotted whiptail, keeled earless lizard, Texas horned lizard, blue spiny lizard, and the northern rose-belly lizard, regarded by some as a full species.
Some representative snakes of the Tamaulipan mezquital include the Tamaulipan hook-nose snake, Tamaulipan milksnake, and Schott’s whipsnake. Other more wide ranging species occurring throughout the region are the Chihuahuan nightsnake, Great Plains ratsnake, gopher snake, long-nose snake, eastern patch-nose snake, and Southern Texas groundsnake. Several species from the tropics reach the northern margin of their distributions in this region including the regal black-striped snake, Central American indigo snake, speckled racer, northern cat-eyed Snake. Venoumous snakes include the Texas coralsnake and western diamond-back rattlesnake, with the western massasauga rattlesnake occurring in the north and the Totonacan rattlesnake occurring in the south.
Amphibians: In spite of the semi-arid environment, enough wetlands are present to support salamanders such as the black-spotted newt and the lesser siren. A second species of siren is known to occur in the lower Rio Grande, thought to be a distant and isolated population of the greater siren by some, or an undescribed species by others. The Rio Grande leopard frog and western narrow-mouthed toad occur in the region along with several toads inhabiting the thorn scrub and grasslands including the green toad, Texas toad, Gulf Coast toad, and cane toad. Many tropical species reach the northern limits of their distributions there such as the Mexican treefrog, white-lipped frog, sheep frog, and the unusual burrowing toad, so unique it is classified in a family by itself.
Fishes: Two species, the San Ignacio pupfish from the upper Rio San Fernando basin near Linares and the swordtail platyfish occurring in the upper parts of the Rio Soto La Maria, in Tamaulipas are endemic to this region. The Amazon molly, is a unisexual species that reproduces through gynogenesis, a form of a form of parthenogenesis. Other fishes found in the area are alligator gar, longnose gar, Rio Grande cichlid, sailfin molly, Rio Grande silvery minnow, San Juan minnow, Tamaulipas shiner, Rio Grande shinner, Gulf killifish, and Rio Grande darter. Two endemic species from this region, the phantom shinner and the Salado shinner, are believed to be extinct.