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# of Endemic Species
134: Rio Conchos
Major Habitat Type:
xeric freshwaters and endorheic (closed) basins
Salvador Contreras Balderas, Universidad Autónoma de Nuevo León. Additional text was modified from Abell et al. 2000. Freshwater Ecoregions of North America: A Conservation Assessment
Part of the Rio Grande complex, this ecoregion encompasses most of central and southern Chihuahua, extending into northern Durango. It is bounded to the north by the Río Grande proper, west by the Río Casas Grandes complex and the summit of the Sierra Madre Occidental, to the east by the plains between Coahuila and Chihuahua, and to the south by the Río Nazas basin complex.
Drainages flowing into:
Río Grande and the Gulf of México
Main rivers or other water bodies:
The main river of this ecoregion is the Río Conchos, which is the main tributary of the Río Grande. Tributaries of the Río Conchos include Río Santa Isabel, Río Satevó, Río San Pedro, and Río Florido. The ecoregion also includes Laguna de Bustillos, Laguna Saúz, and Laguna Mexicanos.
Originating along the eastern slopes of the Sierra Tarahumara, the Río Conchos runs along plains and hills towards its junction with the Río Grande/Río Bravo. Elevations range from 800 to over 3000 m above sea level.
The climate of this ecoregion is temperate semiarid steppe. Mean annual temperature is 15.6 ºC, with a minima and maxima of -3.8 ºC and 32.3 ºC, respectively. Mean annual precipitation is around 450 mm.
Freshwater habitats of the ecoregion include mountain headwaters in Sierra Tarahumara, the middle and lower basin of the Río Conchos, some isolated interior basins that were formerly part of the basin (Laguna Mexicanos, Laguna Bustillos, Laguna Encinillas-Sauz), and semi-isolated springs (San Gregorio, La Hacienda, San Diego).
The Río Conchos is the only free-flowing large river environment left in the Rio Grande basin. It still harbors an impressive assemblage of species because the ecology of this system has not been impacted by channel modifications. This ecoregion is important because it not only supports surface water biota, but also fauna in its specialized spring and cave habitats. These spring habitats contribute most to the ecoregion’s high endemism.
The dominant plant species throughout the Chihuahuan desert is creosote bush (Larrea tridentata), whereas Pinus lumholtzii dominates the eastern slopes of the Sierra Madre Occidental.
The ecoregion contains nearly forty species, many of which are not considered strict endemics to the ecoregion, but are endemic within the larger Río Grande/Río Bravo basin. These species include the Mexican stoneroller (Campostoma ornatum), ornate shiner (Codoma ornata), Río Grande chub (Gila Pandora), Tamaulipas shiner (Notropis braytoni), Chihuahua shiner (N. chihuahua), Río Grande shiner (N. jemezanus), and Conchos pupfish (Cyprinodon eximius).
Description of endemic fishes:
The Río Conchos ecoregion exhibits remarkable endemism in its fish species, with roughly a third of its native fish endemic. Species strictly endemic to the ecoregion include the Conchos shiner (Cyprinella panarcys), largescale pupfish (Cyprinodon macrolepis), bighead pupfish (C. pachycephalus), Bocochi pupfish (C. salvadori), Conchos darter (Etheostoma australe), Chihuahua darter (E. pottsii), yellowfin gambusia (Gambusia alvarezi), and crescent gambusia (G. hurtadoi).
Other noteworthy aquatic biotic elements:
The ecoregion has high endemism among its aquatic herpetofauna; roughly twenty-five percent of its native species are endemic.
The Codoma ornata complex represents an example of stream capture. It attains different levels of divergence between forms in the Río Yaqui, Upper and Lower Río Conchos, headstreams of the Río Fuerte, Río Mayo, Río Mezquital, the interior Laguna de los Mexicanos, Río Nazas and Río Aguanaval. Such divergence seems to have a hub in the Lower Río Conchos that may represent the true Codoma ornata s.s.
This basin has become fragmented and now has several interior basins or isolated springs where speciation of certain groups has been occurring. The cyprinid genus Dionda, the poecilid genus Gambusia (gaigei complex), and the pupfishes of the genus Cyprinodon are composed of two to three undescribed species each in discrete sections or springs in the drainage.
Usually speciation has developed in allopatry, mostly through a combination of barriers and dispersals. The divergence may be exemplified by a number of cases. The series of the cyprinid Cyprinella is represented by forms in different major tributaries of the Río Bravo/Rio Grande. The Río Conchos is represented by C. panarcys.
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 not shared with the rest of Río Grande/Río Bravo complex, and a handful that are endemic to the broader Río Grande/Río Bravo complex. The lower portion of the basin is ecologically “separate” from the rest by Cañón de Peguis, where the fish fauna of the Rìo Conchos stop, and below where the fish fauna of the Río Grande proper begin. Historically, the sierra has isolated the Conchos from the rest of the Río Grande, allowing divergence of fish fauna.
Level of taxonomic exploration:
Reasonable along the middle and lower courses. Not well known in most headwaters on Sierra Tarahumara.
Abell, R. A., Olson, D. M., et al. (2000). "Freshwater Ecoregions of North America: A Conservation Assessment" Washington, DC, USA: Island Press.
Contreras-Balderas, S. (2001)"El Mundo acuático evoluciona" In Lauer, D. (Ed.). Luces y voces del Desierto Chihuahuense. (pp. 30-44) Grupo Cementos de Chihuahua S. A. de C. V..
Contreras-Balderas, S.,Lozano-Vilano, M. L. (1994). "Cyprinella alvarezdelvillari, a new cyprinid fish from Río Nazas of México, with a key to the lepida clade" Copeia 1994(4) 897-906.
Edwards, R. J., Garrett, G. P., et al. (2002)"An ecological analysis of fish communities inhabiting the Rio Conchos basin" In Lozano-Vilano, M. (Ed.). Libro Jubilar en Honor al Dr. Salvador Contreras Balderas. Dir. Gral. De Publicaciones. (pp. 43-62) Monterrey, México: Universidad A. de Nuevo León.
Miller, R. R. (1976). "Four new pupfishes of the genus Cyprinodon from México, with a key to the C. eximius complex" Bull. So. Calif. Acad. Sci. 75 68-75.