Ecoregion Description

132: Upper Rio Grande - Bravo

Major Habitat Type:

temperate upland rivers

Author:

Countries:

Mexico; United States

Boundaries:

This long narrow ecoregion begins in the middle portion of southern Colorado, extending through west-central New Mexico into western Texas. The watersheds of the Rio Grande, from its headwaters to the mouth of the Río Conchos in Mexico, form this ecoregion’s boundary. The eastern extent of this ecoregion is partially defined by the Sangre de Cristo Mountains, while the western extent is defined by the series of ranges that create the Continental Divide. The Rio Grande flows through New Mexico’s major cities, and over 80% of New Mexico’s human population lives along the river (Forest Guardians 1998). In Mexico this river is known as the Río Bravo del Norte.

Drainages flowing into:

During the late Tertiary and early Quartenary the Upper Rio Grande ended in the endorheic basins of south-central New Mexico, Trans-Pecos Texas, and northern Chihuahua; later, during the mid-Pleistocene the upper section joined with the Lower Rio Grande to flow into the Gulf of Mexico (Smith & Miller 1986). 

Main rivers or other water bodies:

Major tributaries to the Upper Rio Grande are the Rio Chama, Rio Puerco and Rio Paraje, and Alamosa rivers. Dams have created the major reservoirs of Elephante Butte, Cochiti, Abiquiu, Angostrura, Isleta, San Acacia and El Vado.

Topography:

The headwaters of the Rio Grand begin in the San Juan Mountains in southern Colorado, and flow through a series of valleys and basins (Smith & Miller 1986).

Climate:

The ecoregion’s climate is primarily arid and semiarid. Precipitation ranges between 150 and 900 mm and temperature averages between 4 and 14^oC (McNab & Avers 1994).

Freshwater habitats:

The Rio Grande’s headwaters are in the San Juan Mountains in southern Colorado, and from there the river flows south through the San Luis Valley and the Rio Grande Depression. The character of the river changes markedly when it exits the depression below El Paso, Texas, and it is this change that signals the break between the Upper and Lower Rio Grande. Streams in the upper portions of this ecoregion tend to have relatively predictable flow regimes and contain fairly diverse habitat types. Further downstream, tributaries are more widely spaced and flow in them is erratic, with the portion of the Rio Grande between El Paso, Texas and the Río Conchos at times virtually dry (Smith & Miller 1986).

Terrestrial Habitats:

Terrestrial habitats in the ecoregion range from coniferous forests to xeric shrublands, sagebrush and grasslands of the Colorado Plateau and Chihuahuan Desert (Ricketts et al. 1999).

Fish Fauna:

With less than 30 native fish species, the Upper Rio Grande is faunistically depauperate compared to the Lower Rio Grande [135], Pecos [133] and Río Conchos [134].

Description of endemic fishes:

There is only one endemic fish species, the White Sands pupfish (Cyprinodon tularosa), which is the only fish species found in three restricted areas in the endorheic Tularosa Basin (Propst et al. 1985; Miller & Smith 1986). The Rio Grande silvery minnow (Hybognathus amarus) was once found in the Upper and Lower Rio Grande [135] as well as the Pecos River [133], but today is restricted to a reach of the Rio Grande between Cochiti Dam and Elephant Butte Reservoir, in central New Mexico.

Other noteworthy fishes:

Historically, the Upper Rio Grande also shared with the Lower Rio Grande the phantom shiner (Notropis orca) and the Rio Grande bluntnose shiner (N. simus simus), both of which are now extinct.

Other noteworthy aquatic biotic elements:

There are no endemic unionid mussels or crayfish, though there are a number of other endemic invertebrates. Within the springs of Socorro County, New Mexico, are the Socorro springsnail (Fontelicella neomexicana), the Chupadera springsnail (Fontelicella sp.), the Alamosa tryonia (Tryonia sp.), the Boquillas isopod (Thermosphaeroma subequalum), and the Socorro isopod (T. thermophilum). There is also an endemic amphibian, the Sacramento mountain salamander (Aneides hardii).

Evolutionary phenomena:

Thermal springs of the Upper Rio Grande support high levels of endemic invertebrates including Fontelicella, Tryonia, and Thermosphaeroma.

Justification for delineation:

Ecoregion boundaries are taken from Abell et al. (2000) and are based on subregions defined by Maxwell et al. (1995).

References/sources:

Abell, R., Olson, D., et al. (2000). "Freshwater ecoregions of North America" Washington, D.C.: Island Press.

Forest, Guardians (1998) "Water and the Rio Grande"

Maxwell, J. R., Edwards, C. J., et al. (1995) "A hierarchical framework of aquatic ecological units in North America (Nearctic Zone)". St. Paul, MN. North Central Forest Experiment Station, USDA Forest Service.

Miller, R. R.,Smith, M. L. (1986)"Origin and geography of the fishes of central Mexico" In Hocutt, C.H.;Wiley, E.O. (Ed.). The zoogeography of North American freshwater fishes. (pp. 487-517) New York, New York, USA: Wiley.

Propst, D. L., Hatch, M. D., et al. (1985) "White Sands pupfish (Cyprinodon tularosa)". New Mex. Dept. Game and Fish, Handbook Spec. Ed. in New Mexico: FISH/CT/CY/TU:1-2.

Ricketts, Taylor H. Dinerstein Eric Olson David M. Loucks Colby J. (1999). "Terrestrial ecoregions of North America: A conservation assessment" Washington, D.C.: World Wildlife Fund.

Smith, M. L.,Miller, R. R. (1986)"The evolution of the Rio Grand Basin as inferred from its fish fauna" In Hocutt, C.H.;Wiley, E.O. (Ed.). The zoogeography of North American freshwater fishes. (pp. 457-485) New York, New York, USA: Wiley.