Lower Rio Grande - Bravo
Salvador Contreras Balderas, Universidad Autónoma de Nuevo León. Additional text modified from Abell et al. 2000.
Major Habitat Type
Temperate floodplain rivers and wetlands
Drainages flowing into
Gulf of México
Main rivers to other water bodies
The Rio Grande/Río Bravo is one of the largest rivers worldwide (2900 km), where it is 22nd in size globally, and 5th in North America. It is one of the three longest bi-national frontiers (2004 km), forming the border between the US and México. Its basin covers an area of about 457,700 km2. This ecoregion comprises the drainage area of the Lower Rio Grande starting just above the mouth of the Río Conchos, with the exception of the basins of the Pecos River , Río Salado , and Río San Juan , each of which support distinct freshwater faunas. Also included in this ecoregion are the watersheds of the San Fernando River, located south of the Rio Grande in Mexico and draining to the Gulf of Mexico, and the Devil’s River, a tributary to the Rio Grande directly to the east of the Pecos River.
This ecoregion is defined primarily by the Rio Grande, or Río Bravo del Norte, from its confluence with the Río Conchos to the Gulf of Mexico. The ecoregion covers a small part of southwestern Texas, and in Mexico parts of eastern Chihuahua, northern Coahuila, the extreme northern section of Nuevo León, and northern Tamaulipas. The Río Conchos borders the western part of the ecoregion, and the Gulf of México borders the east.
Gently undulating hills characterize the upper part of the ecoregion, tapering to lowlands towards the sea. Elevations range from sea level to over 3500 m, although relief rarely exceeds 100 m.
Freshwater habitats of this large river system include floodplains in the middle and lower basin, small creeks within the central portion, springs, and caves. Within the lower basin large diversified springs are habitats for a variety of fish, many of which are endemic.
One outstanding feature of the Lower Rio Grande is the area known as Zona Carbonifera. This is a subterranean aquifer with an extensive system of springs and caves associated with it. A distinctive cave fauna occurs here, which is imperiled by overuse of the aquifer’s water.
The Rio Grande/ Río Bravo basin is being dewatered and salinized, suffering from a heavy invasion of brackish water. As a result, lowland fish fauna has expanded up to 800 km upstream, forcing the extirpation of freshwater species.
The ecoregion is dominated by three terrestrial ecoregions: Chihuahuan Desert in the northwest, Tamaulipan mezquital in the central and lower portion, and Western Gulf coastal grasslands along the coast.
Tamaulipan mezquital, which covers a majority of the ecoregion, is a mesquite grassland that includes mesquite (Prosopsis glandulosa), various species of acacia such as Acacia smallii and A. tortuosa, desert hackberry (Celtis pallida), javelina bush (Condalia ericoides), cenizo (Leucophyllum frutescens), common bee-brush or white brush (Aloysia wrightii), Texas prickly pear (Opuntia lindheimeri), and tasajillo or desert Christmas cactus (Cylindropuntia leptocaulis) (WWF 2001).
Description of endemic fishes
Species endemic to the ecoregion include the Devil’s River minnow (Dionda diaboli), Big Bend gambusia (Gambusia gaigei), and spotfin gambusia (Gambusia krumholzi). Near-endemics include the Rio Grande silvery minnow (Hybognathus amarus), phantom shiner (Notropis orca), and bluntnose shiner (N. simus).
Justification for delineation
Ecoregion delineations were based on qualitative similarity/dissimilarity assessments of major basins, using the standard administrative hydrographical regions of the Mexican federal government.This ecoregion has numerous strict endemics, many of which are shared with neighboring areas, or are endemic to the Rio Grande basin. The relict groups of Neotropical taxa make this ecoregion distinct from other areas of the Rio Grande basin.
Level of taxonomic exploration
The level of taxonomic exploration along the Rio Grande/Río Bravo is reasonable along middle and lower courses, but poor in most headwaters.
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