Ecoregion Description

161: Guzman - Samalayuca

Major Habitat Type:

xeric freshwaters and endorheic (closed) basins

Author:

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

Countries:

Mexico; United States

Boundaries:

Part of the Rio Grande complex, this ecoregion covers most of the Mexican state of Chihuahua and extends into southwestern New Mexico. A small portion of the ecoregion is found in northeastern Sonora and extreme southeastern Arizona. The southwestern extent of this ecoregion is defined by the mountains of the Sierra Madre Occidental. Additionally, a small portion of the ecoregion lies on the western side of the Continental Divide within Arizona.

Drainages flowing into:

This ecoregion incorporates the interior drainages that were formed after the diversion of the upper Rio Grande during the mid-Pleistocene.

Main rivers or other water bodies:

The primary water bodies in the ecoregion include the Río Casas Grandes, Río Santa María, Río Ahumada, Laguna de Bavícora, Llanos de Samalayuca, and Río Carmen.

Topography:

Topography ranges from the hills and plains of the Chihuahuan desert to the rugged Sierra Madre Occidental, where peaks may exceed 3000 m.

Climate:

Most of the ecoregion lies within a semiarid steppe climate zone (Bhk), characterized by hot summers and highly variable diurnal and seasonal temperatures. Mean annual temperatures range between 6-20 ºC, and average 14 ºC. Mean annual precipitation averages 360 mm, but may reach 900 mm in the Sierra Madre Occidental.

Freshwater habitats:

Freshwater habitats in this ecoregion include creeks, rivers, and springs. Most basins in this complex include headwaters, middle reaches, and terminal lagoons. Part of this ecoregion is the region known as Médanos Samalayuca, a harsh area of parched sand dunes that was once the bed of an ancient lake.

Fish Fauna:

This ecoregion includes nearly forty species, including Mexican stoneroller (Campostoma ornatum), ornate shiner (Codoma ornate), Mexican roundtail chub (Gila minacae), and fathead minnow (Pimephales promelas) (Cyprinidae); Rio Grande sucker (Catostomus plebeius) (Catostomidae); and Yaqui catfish (Ictalurus pricei) (Ictaluridae).

One important site for the conservation of freshwater biodiversity in this ecoregion is the Mimbres River of New Mexico. The fish fauna of the Mimbres River consists of just three confirmed species: Chihuahua chub (Gila nigrescens), beautiful shiner (Cyprinella formosa), and Rio Grande sucker.

Description of endemic fishes:

As is typical of many endorheic habitats, the Guzmán - Samalayuca ecoregion is rich in endemic species. Species that are strictly endemic to the ecoregion include the largemouth shiner (Cyprinella bocagrande), carbonera pupfish (Cyprinodon fontinalis), and Chihuahua chub (Gila nigrescens). Near-endemics include the Cahita sucker (Catostomus cahita), Bavispe sucker (C. leopoldi), whitefin pupfish (Cyprinodon albivelis), and Palomas pupfish (C. pisteri).

Evolutionary phenomena:

The ecoregion is composed of several interior drainages, intimately related, and postulated to have been part of a single system in the Pleistocene. The resulting fragmentation and isolation resulted in the divergence of several stocks of the catostomids (Catostomidae), shiners (Cyprinidae), and pupfish (Cyprinodontidae).

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. High endemicity of several taxa, as indicated in the species list, evolved through the isolation of springs and interior basins that comprise the ecoregion.

Level of taxonomic exploration:

Deficient. There are few roads near headwaters.

References/sources:

Abell, R. A., Olson, D. M., et al. (2000). "Freshwater Ecoregions of North America: A Conservation Assessment" Washington, DC, USA: Island Press.

Miller, R. R., Minckley, W. L., et al. (2005). "Fishes of México" Chicago Univ. Press.

Minckley, W. L., Miller, R. R., et al. (2002). "Three new pupfish species, Cyprinodon (Teleostei, Cyprinodontidae), from Chihuahua, México and Arizona, USA" Copeia 3 687-705.

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.